March 12, Vasu Demla, LLC 3525 Sandy Trail Lane Plano, TX Attention: Mr. Suraj Sunny Demla

Transcription

1 March 12, 2012 Vasu Demla, LLC 3525 Sandy Trail Lane Plano, TX Attention: Mr. Suraj Sunny Demla Re: Report of Subsurface Exploration and Geotechnical Study for the Proposed Home2 Suites Development 300 South Texas Avenue; College Station, Texas CSC Project Number: Dear Mr. Demla: This letter transmits one (1) bound original report prepared by CSC Engineering & Environmental Consultants, Inc. (CSC) for the Proposed Home2 Suites Development in College Station, Texas. The report documents the subsurface exploration and geotechnical study conducted by CSC for the proposed building and associated paved areas that are planned as part of the Home2 Suites Development which will be located at 300 South Texas Avenue in College Station, Texas. The transmitted report is entitled Report of Subsurface Exploration and Geotechnical Study; Proposed Home2 Suites Development; 300 South Texas Avenue; College Station, Texas. All of the work presented in the report was performed in accordance with CSC s proposal to Vasu Demla, LLC that was dated February 2, The proposal was accepted by Suraj Demla on behalf of Vasu Demla, LLC on February 6, We sincerely appreciate the opportunity to have performed this work for Vasu Demla, LLC and Jones & Carter, Inc. We look forward to continuing our working relationship in the future. Please do not hesitate to contact us at (979) if you have any questions or need additional information concerning this matter. Sincerely, M. Frederick Conlin, Jr., PE Senior Engineer MFC:rc Via [surajdemla@yahoo.com] and U.S. Mail cc: Jones & Carter, Inc Briarcrest Drive Suite 160 Bryan, TX Attention: Mr. Derek Walton Via: [DWalton@jonescarter.com] 3407 Tabor Road Phone (979) Bryan, Texas Fax (979)

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3 1.0 INTRODUCTION PROJECT DESCRIPTION Sources(s) of Project Information General Description of Proposed Structure Preferred Foundation System for Proposed Structure Site Paving Site Grading OBJECTIVES AND SCOPE OF THE EXPLORATION AND STUDY REPORT FORMAT FIELD EXPLORATION PROGRAM PLAN OF SUBSURFACE EXPLORATION DRILLING AND SAMPLING GROUND WATER OBSERVATION BORING LOGS SAMPLE CUSTODY LABORATORY TESTING PROGRAM CLASSIFICATION TESTS AND MOISTURE CONTENT TESTS STRENGTH TESTS AND DRY UNIT WEIGHT DETERMINATIONS SITE CONDITIONS GENERAL SURFACE CONDITIONS GENERAL SUBSURFACE STRATIGRAPHY Soil Classification Criteria General Description of Subsurface Stratigraphy at Boring Locations Limitations of Generalized Descriptions of Subsurface Stratigraphy at Boring Locations GROUND WATER LEVEL OBSERVATIONS GENERAL ANALYSIS AND RECOMMENDATIONS GENERAL CONSIDERATIONS GENERAL CONSIDERATIONS OF SHRINK-SWELL MOVEMENTS OF SOILS AND INFLUENCE ON FOUNDATION SYSTEMS MAGNITUDES OF POTENTIAL SHRINK-SWELL MOVEMENTS Calculation of Magnitudes of Potential Total Shrink-Swell Movements for Existing Soils Stratigraphy Reduction in Magnitudes of Potential Shrink-Swell Movements through the Excavation and Replacement Scheme General Building Pad Design and Construction Techniques TYPES OF FOUNDATION SYSTEMS CONSIDERED Advantages and Disadvantages of the Various Types of Foundation Systems RECOMMENDED TYPE OF FOUNDATION SPECIFIC FOUNDATION RECOMMENDATIONS DRILLED PIER AND STRUCTURAL FLOOR FOUNDATION SYSTEM (TYPE I FOUNDATION SYSTEM) GENERAL DRILLED AND UNDERREAMED PIER FOUNDATIONS Design of Drilled and Underreamed Piers Founding Depth and Founding Formations Design of Drilled and Underreamed Piers Allowable Bearing Pressures Design of Drilled and Underreamed Piers Positive Skin Friction Design of Drilled and Underreamed Piers Pier Settlement Design of Drilled and Underreamed Piers Upward Acting Tensile Forces on Pier ii

4 6.2.6 Design of Drilled and Underreamed Piers Spacing of Shafts (In Consideration of Group Action) Design of Drilled and Underreamed Piers Construction Considerations STRUCTURAL FLOOR SLAB SYSTEM SPECIFIC FOUNDATION RECOMMENDATIONS - DRILLED PIER, SUPPORT OF GRADE BEAMS AND COLUMNS, WITH SUBGRADE-SUPPORTED FLOOR SLAB (TYPE II FOUNDATION SYSTEM) GENERAL PIER AND STRUCTURAL GRADE BEAM DESIGN VALUES SUBGRADE-SUPPORTED FLOOR SLAB SYSTEM Slab Grade Beams or Footing Founding Depth Footing Bearing Values Potential Total and Differential Vertical Movements Building Pad Preparation Architectural and Structural Element Detailing to Minimize Effects of Foundation Movement PAVEMENT RECOMMENDATIONS GENERAL DESIGN CRITERIA USED FOR PAVEMENT ANALYSES ANTICIPATED PROJECT TRAFFIC CONDITIONS AND VEHICLE CHARACTERISTICS SUBGRADE CLASSIFICATION PAVEMENT THICKNESS REQUIREMENTS PAVEMENT SYSTEM MAINTENANCE Pavement Drainage Pavement Maintenance RECOMMENDATIONS FOR ANCILLARY STRUCTURES SWIMMING POOL General Subsurface Conditions Foundation Recommendations CONSTRUCTION CONSIDERATIONS SITE PREPARATION (CLEARING, STRIPPING AND DEMOLITION PREPARATION OF BUILDING PAD SUBGRADE AND OTHER FILL AREA SUBGRADES Building Pad Excavation Proof Rolling Subgrade Soils Compaction and Testing GENERAL STORM WATER DRAINAGE AND MOISTURE CONTROL CONSIDERATIONS Building Pad Areas Drainage and Moisture Control Considerations Site Drainage Considerations BUILDING AREA ( SELECT ) FILL AND GENERAL PAVEMENT AREA FILL MATERIAL SELECTION AND PLACEMENT PROCEDURES DRILLED PIER EXCAVATIONS SHALLOW GRADE BEAM EXCAVATIONS FOUNDATION CONCRETE BASIS OF RECOMMENDATIONS LIST OF TABLES iii

5 Table 1. Calculated Potential Total Vertical Movements for Various Depths of Excavation of Existing Soils and Replacement with Select Fill Soils Table 2. Recommended Unit Net Allowable Bearing Pressures for Pier Foundation Elements Table 3. Recommended Allowable Unit Side Resistance (Skin Friction or Adhesion) Values Table 4. for Pier Foundation Elements Recommended Unit Net Allowable Bearing Pressures for Continuous Footing Foundation Elements Founded in Natural Soils or in Compacted Select Fill Soils Table 5. Pavement Thickness Schedule for Conventionally Reinforced and Jointed PCC Access Drive and Circulation Lanes within Parking Areas (Medium-Duty Pavement Section) Table 6. Pavement Thickness Schedule for Conventionally Reinforced and Jointed PCC in Parking Space Areas (Light-Duty Pavement Section) LIST OF APPENDICES Appendix A Project Figures Figure 1 - Project Vicinity Map Figure 2 - Site Plan and Plan of Borings Figure 3 - Subsurface Profile A-A Boring Logs Key Sheet to Terms and Symbols Used on the Boring Logs Appendix B Summary of Laboratory Test Results iv

6 1.0 INTRODUCTION This report documents the results of the subsurface exploration and geotechnical study at the site of the proposed Home2 Suites Development. The exploration and study were performed by CSC Engineering & Environmental Consultants, Inc. (CSC) for Vasu Demla, LLC. The site of the proposed development is located on the western side of South Texas Avenue between University Drive and Hensel Street in College Station, Texas, as illustrated on Figure 1 Project Vicinity Map in Appendix A of this report. The study was performed in accordance with CSC s proposal to Vasu Demla, LLC dated February 2, The proposal was accepted by Suraj Demla on behalf of Vasu Demla, LLC on February 6, Field activities for this project were initiated on February 7, 2012 and subsequently completed on February 9, Laboratory testing of selected soils recovered from the field investigation was completed on February 23, A summary description of the subsurface information developed from the field and laboratory phases of the project, an outline of our interpretation of the information, a discussion of possible foundation options, and recommendations concerning foundation support of the proposed structure and associated paved areas are presented in this report for your review and consideration. 1.1 PROJECT DESCRIPTION Sources(s) of Project Information Information concerning the proposed project was initially obtained from Mr. Derek Walton with the civil design firm of Jones & Carter, Inc. Mr. Walton provided a site plan for the proposed development that indicated the project would consist of a 5-story motel building, paved entry/exit drives, circulation lanes, and parking areas, and relocation of a large utility pole. Each of these project elements is described in greater detail in the following subsections of this report except for the utility poles which was addressed in a separate interim report that was issued on February 24, In addition, CSC received information from Mr. Anil Ram of ADR Designs, LLC in an communication of February 1, 2012 concerning the type of building superstructure that will be used and 1

7 the preferred foundation system for the building. Mr. Ram also indicated in his the number of borings to be included in the proposed subsurface investigation. We understand that the proposed project will consist of a single motel structure with associated paved drive and parking areas as illustrated on Figure 2 Site Plan and Plan of Borings in Appendix A. Each of these project elements is discussed in the following sections of this report General Description of Proposed Structure We understand the proposed motel building will be a 5-story structure with an area of approximately 12,000 square feet for each level of the building. The building will have a superstructure framing system that is a combination of structural steel and conventional FRTW (fire retardant treated wood) frame or wood-stud bearing wall with exteriors consisting of a combination of wood, brick and stone. The design structural loads that will be transmitted to the foundation system are not known at the present time but we anticipate that the building will typically have maximum bearing wall line loads on the order of 4.5 kips ( kilopounds ) per linear foot of wall (klf), and that there will also be some locations where there will be maximum point loads of approximately 80 to 100 kips. We expect that the continuous or sustained loads will be in the order of 50 to 60 percent of the maximum loads. We do not believe that the building will have unusual floor loads other than those associated with a typical motel building. We do not anticipate that the floor slab will have extremely movement sensitive floor coverings such as ceramic or marble tile. In addition to the proposed building, we understand that there will be a 2,000 square foot pool constructed at the eastern end of the building. We anticipate that the pool will have a maximum depth of approximately 6 feet and will be constructed of reinforced gunite. The proposed building will not have a basement, storm shelter, sump pit, service pit, or equipment pit that will require structural excavations at the site Preferred Foundation System for Proposed Structure We believe that the building owners and their design team prefer to use a deep foundation system that incorporates drilled and underreamed piers to support the columns and load bearing walls of the building but that the building floor slabs will be supported on a subgrade that is part of a building pad composed of a considerable thickness of select fill soils. We do not anticipate that movement sensitive floor coverings, such as ceramic or marble tiles, will be placed over any significant portion of the floor slab. We also understand that any potential shrink-swell movements of the foundation soils that might 2

8 adversely impact the performance of the subgrade supported floor systems will been considered in the design of the floor systems and that the risk of foundation movement can be accepted by the developer in return for the lower construction costs associated with the use of subgrade supported slabs Site Paving We understand that the proposed paved area will include a main entry/exit drive to South Texas Avenue, a secondary entry/exit drive in the rear of the development to Meadowland Road, internal circulation lanes, and approximately 100 individual parking spaces. We anticipate that the paved areas will have rigid pavement sections consisting of Portland cement concrete (PCC) surfaces over chemically stabilized subgrades. Specific traffic information for the proposed paved areas is not known at the present time, but we anticipate that the paved areas will primarily be used by light passenger vehicles with some occasional use by light to medium weight delivery trucks. We do not anticipate that any significant volume of heavy weight trucks will use the on-site paved areas Site Grading Grading plans for the proposed development have not been finalized at the time of this report. However, we have noted that the higher elevations are in the rear of the site near Meadowland Road, and the lower elevations are in the front of the site adjacent to South Texas Avenue. Consequently, we believe that there will be some fill added to the front portion of the site to elevate final grades above the surrounding ground surface, although it is possible that such fill will not be required to create the proposed building pad. We believe that there is currently approximately 1.6 feet change in elevation of the ground surface across the length of the proposed building from approximately EL at the southern corner of the building to approximately EL 329 in the northern corner. However, we understand that preliminary grading plans call for the finished floor (FF) slab of the proposed building to be at EL 328. As a result, we anticipate that the building pad will be created by excavation or cut in the existing soils and that no fill may be required to create the proposed building pad. However, we do understand that consideration will be given to excavation of existing soils of moderate to high plasticity from the building area and replacing the excavated soils with a significant thickness of select fill soils to create a thick building pad and to thereby reduce the magnitudes of potential shrink-swell movements for the building floor slab. We believe that the building pad constructed of select fill soils will be uniform in thickness across the entire length of the proposed building. 1.2 OBJECTIVES AND SCOPE OF THE EXPLORATION AND STUDY The specific objectives of the exploration and study were to: 3

9 Secure information on the general subsurface conditions by drilling three (3) borings across the site of the proposed building area, one (1) boring in the area of the proposed utility pole relocation, and four (4) borings in the proposed paved areas and testing in the laboratory selected soil samples recovered from the borings. Evaluate the subsurface information developed from the field exploration and laboratory testing programs. Develop general recommendations based upon an engineering analysis of the subsurface information to guide the formation of the conceptual foundation and final design plans for the proposed foundation system for the proposed building and paved areas. It should be recognized that the exclusive purpose of this study was to develop general recommendations for the foundation of the proposed building and associated paved areas. This study did not directly assess, or even attempt to address, specific environmental conditions encountered at the site (i.e., the presence of pollutants or other substances in the soil, rock, or ground water). In addition, this geotechnical study did not specifically address historical uses of the site and the surrounding areas from an environmental perspective. 1.3 REPORT FORMAT The following sections of this report initially present in Sections 2 and 3 the descriptions of work and test procedures employed to collect the subsurface information for the project. In addition, Appendix A presents additional information concerning the field exploration in the form of a vicinity map indicating the approximate location of the proposed motel building and paved areas, a plan of boring illustrating where the various borings were drilled, the log of the exploratory borings indicating the types of soils encountered at the boring locations, and a symbol key sheet describing the terms and symbols used on the logs of boring. Appendix B contains the summary results of the laboratory-testing program. Section 4 presents a general description of surface conditions at the site as well as a description of the subsurface stratigraphy at the boring location based upon an evaluation of the field exploration information and the laboratory test results. Ground water observations are also discussed in Section 4. Next, Section 5 presents a general analysis of the subsurface information and a general discussion of possible alternative foundation systems that should be considered for the proposed structure. Specific recommendations and design values for the two (2) types of foundation support that we believe are being actively considered for the proposed building are presented in Sections 6 and 7 of this report. Section 6 discusses a drilled pier and structurally suspended floor foundation system and Section 7 discusses a drilled pier with a subgrade-supported floor foundation system. 4

10 Section 8 gives CSC s evaluation of existing and proposed subgrade soils in the areas proposed for paving and offers recommendations for the design and construction of a rigid pavement system in the access drive, the circulation lanes, and the parking space areas. The recommendations also include a discussion of subgrade soil preparation. Section 9 of the report offers a discussion of foundation considerations for ancillary structures associated with the proposed development, such as the swimming pool. Section 10 offers a discussion of site development and construction considerations and specific guidance with respect to subsurface conditions that may impact site development and construction operations. Recommendations concerning preparation of building pad and the necessity of controlling construction and post-construction drainage are also included in Section 10, as are recommendations for general material requirements and placement procedures. Finally, Section 11 presents the basis for the recommendations given in the report and the general limitations for the information presented. 5

11 2.0 FIELD EXPLORATION PROGRAM 2.1 PLAN OF SUBSURFACE EXPLORATION Subsurface conditions were explored by drilling a total of eight sample borings across on the site. Three (3) of the borings, which were designated as borings B-1 through B-3, were drilled in the proposed building area to depths ranging from 30 to 50 feet below the existing surface grade. The single boring designated as B-4 was drilled to a depth of 40 feet in the area of the proposed utility pole relocation. The remaining four (4) borings, which were designated as borings B-5 through B-8, were drilled in the proposed paved areas to depths of approximately 6 feet. All of the boring depths are referenced to the surface grade existing at the specific boring locations at the time of the field study. The boring locations were established with respect to existing surface features at the site using a 100-foot tape and turning right angles to designated features, such as existing buildings, trees, fences, roads, etc. It should be recognized that the degree of accuracy in locating the boring is commensurate with the manual layout techniques utilized. The approximate locations of the borings on the site are indicated on the previously referenced Figure 2. As previously indicated, the boring depths are referenced to the ground surface elevation existing at the specific boring location at the time of the field exploration. If adjustments to the present surface elevations are made as part of site grading operations prior to construction of the foundation system, then some adjustment in the recommended foundation depths as presented in subsequent discussions in this report and some modifications of related foundation recommendations may be necessary. Any required adjustments can be made following a review of final grading plans and a comparison of the existing topography present at the time of the field study and the final elevations established by the final grading and drainage plan. The locations of the borings are currently marked in the field with a wooden lathe with white flagging. We strongly recommend that the boring locations and the surface elevations at the boring locations be defined as part of the topographic survey being performed for the project. An accurate determination of the boring location and the surface elevations at the boring location will help to minimize the potential for misinterpretation of foundation recommendations presented in this report. 6

12 2.2 DRILLING AND SAMPLING Field drilling activities associated with the subsurface exploration of the site were initiated on February 7, 2012 and completed on February 9, The borings were all drilled with a truck mounted Mobil B-60 rotary drilling rig. The shallow borings and one of the deeper borings drilled at the site were advanced using dry auger drilling techniques to the full depth of exploration. However, three (3) of the deep borings drilled in the area of the proposed building and in the area of the proposed utility pole relocation were initially drilled using dry auger drilling techniques, but drilling fluids were introduced into the boreholes when ground water was first encountered in order to stabilize any wet, caving soils along the sidewalls of boreholes and the boring was advanced to the completion depths using wet or wash rotary drilling methods. Representative soil samples were obtained continuously to a maximum depth of 6 feet in the paving area borings and 10 feet in the building and utility pole area borings, and thereafter, samples were obtained at 5-foot intervals in the building area borings to the depths of maximum exploration. Samples of cohesive soils (i.e. clays) and granular-cohesive soils (i.e., sandy clays) were generally obtained by mechanically pushing a 3-inch-diameter, thin-wall Shelby-tube sampler into the soils in general accordance with the procedures outlined in ASTM D Standard Practice for Thin-Walled Tube Sampling of Soils for Geotechnical Purposes. The granular or cohesionless soils (i.e., sands) and the cohesive-granular soils (i.e., clayey sands) present within the stratigraphy at the boring locations were also sampled during the performance of the Standard Penetration Tests (SPT) which were performed in general accordance with the procedures outlined in ASTM D 1586 Standard Test Methods for Penetration Test and Split-Barrel Sampling of Soils. The SPT involves driving a 2-inch diameter split-barrel sampler into the soils. The spilt-barrel or split-spoon sampler is driven into the soil for three successive 6-inch increments with blows from a 140-lb hammer. The vertical travel of the hammer was 30 inches in accordance with ASTM D The number of blows required to drive the sampler over the depth interval from 6 to 18 inches is defined as the standard penetration number (and is represented by the letter N). However, if a limiting blow count of 50 blows is reached during any 6-inch interval, the test is terminated and an N-value of 50 is recorded along with the corresponding penetration in inches. Test termination also occurs if a total of 100 blows have been applied or if the sampler has not advanced after 10 successive hammer blows. The N-values determined for the SPTs are recorded as part of the performance of the test. The types of samples and the corresponding depths at which samples were collected, as well as results of any field tests, are presented at referenced depth intervals on the individual boring logs in Appendix A. 7

13 2.3 GROUND WATER OBSERVATION As previously indicated, the borings were drilled utilizing dry auger drilling techniques so that the presence of ground water could be observed during and immediately following completion of the drilling operations. Ground water observations were made during drilling operations. However, when ground water was encountered, drilling fluids were used to stabilize the borehole and further ground water observations could not be made. The ground water observations are discussed in Section 4 of this report. Subsequent to the completion of drilling activities, the boreholes were filled with soil cuttings and covered as a safety precaution for pedestrian traffic that might traverse the site and longer term ground water observations could not be made. 2.4 BORING LOGS A field geotechnologist was present during the field exploration to describe the subsurface stratigraphy and to note obvious anomalies in the subsurface stratigraphy that may have been present at the specific boring locations. Descriptions of the subsurface conditions encountered at the boring locations are shown on the individual boring logs presented in Appendix A of this report. The Key to Symbols and Soil Classification sheet explaining the terms and symbols used on the log is presented immediately following the logs. The logs represent CSC s interpretation of the subsurface conditions based upon the field geotechnologist s notes together with engineering observation and classification of the materials in the laboratory. The lines designating the interfaces between various strata represent approximate boundaries only, as transitions between formations may be gradual. 2.5 SAMPLE CUSTODY All samples of subsurface materials obtained in the borings were removed from the samplers and visually classified in the field. Representative samples were sealed in appropriate packaging and placed in core boxes for transportation to the laboratory for further analysis. The samples will be stored for at least 30 days following the date of this report. At the end of the 30-day storage period, the samples will be discarded unless a written request is received from the owner requesting that the samples be stored for a longer period. 8

14 3.0 LABORATORY TESTING PROGRAM Samples of subsurface materials recovered from the boring were examined and classified by the geotechnical engineer and various laboratory tests assigned by the geotechnical engineer for selected samples. The laboratory tests were performed to aid in foundation soil classification in accordance with the Unified Soil Classification System (ASTM D Standard Test Method for Classification of Soils for Engineering Purposes (Unified Soil Classification System). Visual classification of soil samples that were not tested was also performed in accordance with the procedures outlined in ASTM D Standard Practice for Description and Identification of Soils (Visual-Manual Procedure). The laboratory-testing program also employed strength tests to determine the engineering characteristics of the foundation materials. The laboratory testing program activities for this project were completed on February 23, The laboratory test results are presented in a summary tabular form in Appendix B. In addition, the laboratory test results are also presented both numerically and symbolically on the individual boring log in Appendix A. As previously stated, the symbols and terms used on the log of boring are explained both on the log and also on the Key to Symbols and Soil Classification sheet presented immediately following the log. 3.1 CLASSIFICATION TESTS AND MOISTURE CONTENT TESTS As previously indicated, laboratory tests were performed in order to classify the foundation soils in accordance with the USCS and to determine the soil-moisture profile at the boring locations. The classification tests consisted of Atterberg limit determinations (liquid limit and plastic limit) and grainsize distribution determinations. The Atterberg limit determinations were performed in general accordance with the procedures outlined in ASTM D Standard Test Methods for Liquid Limit, Plastic Limit, and Plasticity Index of Soils. In addition to the selected Atterberg limit tests, grain-size distribution tests were also performed. The percent of soil particles passing the U.S. Standard sieve size No. 200 was the only particle size determination made on the recovered samples and was determined by washing the soils through the No. 200 sieve in accordance with the procedures outlined in ASTM D Standard Test Method for Amount of Material in Soils Finer Than No. 200 (75 µm) Sieve. The soil fractions passing the No. 200 sieve size are the silt- and clay-size particles and are generally referred to as fines. The percentage of soil sample particles that were larger and finer than the 75 µm size (i.e., the size retained on the U.S. Standard No. 200 sieve size) was the only gradation analysis performed for this project. 9

15 The natural moisture content of individual samples was determined in accordance with the procedures outlined in ASTM D Standard Test Methods for Laboratory Determination of Water (Moisture) Content of Soil and Rock by Mass. 3.2 STRENGTH TESTS AND DRY UNIT WEIGHT DETERMINATIONS Emphasis was also directed toward an evaluation of the strength or load-carrying capacity of the foundation soils. Strength tests were performed to develop an estimate of the undrained cohesion or c- value of the soils. The strength tests performed for this project consisted of the unconfined compression test, the unconsolidated-undrained triaxial compression test, and the hand or pocket penetrometer tests. The unconfined compression test was performed in the laboratory on relatively undisturbed samples of cohesive soils to determine the compressive strength characteristics. The test procedures outlined in ASTM D Standard Test Method for Unconfined Compressive Strength of Cohesive Soil were utilized. The unit dry weight was also determined for each unconfined compression test sample in accordance with the procedures outlined in ASTM D The shear strength of the clays with significant sand content was determined by performing the unconsolidated-undrained triaxial compression test in accordance with the procedures outlined in ASTM D a (2007), Standard Test Method for Unconsolidated-Undrained Triaxial Compression Test on Cohesive Soils. The unit dry weight of each triaxial compression test sample was also determined. Finally, hand or pocket penetrometer tests were also performed both in the field and in the laboratory on relatively undisturbed soil samples. The hand or pocket penetrometer tests provide only an approximate indication of the unconfined compression strength of the soils. Experience with similar soil conditions in the vicinity of the proposed project site has indicated that the hand penetrometer tests tend to overestimate the unconfined compression strength of the soil samples. 10

16 4.0 SITE CONDITIONS 4.1 GENERAL SURFACE CONDITIONS As can be seen from a review of the previously referenced Figure 2, the site of the proposed development is L-shaped. The front leg of the L is oriented in a northeast to southwest direction and is perpendicular to South Texas Avenue. The second rear leg of the L is oriented is a northwest to southeast direction and is parallel to Meadowland Road. Both portions of the site have been previously developed. We understand that a motel building was previously present on the front leg of the site, and we have observed that four (4) apparently abandoned quadplex buildings and associated paved areas are present on the rear leg of the site. The front leg of the site has concrete and gravel paving and portions of a brick wall or sign adjacent to South Texas Avenue and may represent the remnants of a previously existing building. The middle portion of the front leg of the site is elevated approximately 5 feet above the front portion of the site and is covered with short native grasses, a concrete basketball court, and a concrete utility pad. The rear leg of the site has four (4), two-story quadplex buildings which appear to be of wood construction with brick exteriors, plus associated HMAC and PCC paved drive lanes and parking areas. As previously indicated, there are pronounced topographic changes across the site. The highest existing ground surface elevations are present across the rear portion of the site. The ground surface elevation in this area ranges from approximately EL. 330 to EL. 332 and gradually slopes in a northeasterly direction towards South Texas Avenue. The ground surface drops across a steep slope from approximately EL 328 to EL 323 at a point approximately 130 feet distance from South Texas Avenue and gradually slopes downward to approximately EL 321 along South Texas Avenue. 4.2 GENERAL SUBSURFACE STRATIGRAPHY The soils encountered at the various boring locations were generally described and classified in accordance with the criteria set forth in the previously referenced USCS. Classification of the soils was primarily based upon the test results derived from the laboratory-testing program performed for the various soils strata within the stratigraphy, but visual-manual classification of some of the soils was also utilized in conformance with the previously referenced ASTM procedures. The USCS guidelines used in the classification of the soils are generally discussed in the following Section of this report. A general and idealized description of the stratigraphy present at the boring location is presented in Section of this report. 11

17 4.2.1 Soil Classification Criteria The laboratory-performed classification tests consisted of determining the percent fines of the soils and of determining the Atterberg limits of the soils as explained in the following paragraphs. The percentages of fines, i.e., the silt- and clay-size particles, were measured by determining the percentage of soils that would pass through or be finer than the No. 200 U.S. Standard sieve size. The openings in the No. 200 sieve are approximately 75 µm (microns) in width, which roughly corresponds to the smallest size soil particle that can be seen by the naked eye (i.e., unaided by a microscope). The particles that are retained on the No. 200 sieve are referred to as granular soils and consist of sands and gravels. Thus, the portion of the sample that does not consist of fines represents granular soils, and typically only sands. Soils with a percent fines content of 50 percent or greater would classify as clays or silts under the USCS. Conversely, by definition, sands and/or gravels would have a percentage of fines of less than 50 percent. Sands are designated by the letter S under the USCS and modifiers such as M or C are used to designate silty sands (SM) or clayey sands (SC), respectively. Pure sands are given the designators W and P to represent well graded sands (SW) or poorly graded sands (SP). The Atterberg limit tests are composed of the liquid limit (LL) test and the plastic limit (PL) test, along with the shrinkage limit test. The LL and PL tests were performed as part of the classification testing of the present study. These limits distinguish the boundaries of the several consistency states of plastic soils. The LL represents the moisture content at which the soil is on the verge of being a viscous fluid (i.e., a very wet condition), and the PL represents the moisture content at which the soil behaves as a non-plastic material (i.e., a slightly moist condition). The plasticity index (PI) of soil is defined as the range of moisture contents at which the soil behaves as a plastic material and is defined as the difference between the liquid limit and the plastic limit (LL - PL = PI). The magnitude of the PI of a soil is typically considered to be an indication of the clay content and the volumetric change (shrink-swell) potential of the soils (although the volumetric change can also vary with the type of clay mineral and the nature of the ions adsorbed on the clay surface). Although the soil classifications utilized in the subsequently presented descriptions and discussions generally follow the criteria established by the USCS, there is one exception with respect to clays of moderate plasticity that are designated by the letters CM. Highly plastic clays with a liquid limit equal to or greater than 50 are given a CH designation (C for clays and H for high plasticity) under the USCS. Clays with liquid limits lower than 50 are designated as CL (L for low plasticity) soils under the current USCS. However, when Arthur Casagrande performed the original work for the soil classification system, he proposed an intermediate classification in which clays with a liquid limit between 30 and 49 were termed CM (M for moderate) soils, or clays of moderate plasticity. Although not adopted by ASTM, 12

18 the CM designation is still sometimes used to describe in greater detail the soils with plasticities between the low and high ranges General Description of Subsurface Stratigraphy at Boring Locations As previously mentioned, the subsurface stratigraphy at the eight (8) boring locations drilled across the site of the proposed development is presented in detail on the individual boring logs contained in Appendix A. The boring logs should be consulted for a detailed description of the stratigraphy at a particular location on the site. The stratigraphy indicated by the soils recovered from the borings is graphically depicted on Figure 3 Subsurface Profile A-A in Appendix A. Please note that the soil stratum division lines shown on Figure 3 may not be continuous between the boring locations and subsurface conditions between the boring locations may differ from those depicted on Figure 3. In general, the subsurface stratigraphy can be described as consisting of five (5) different stratigraphic zones: (1) a surficial zone composed of variable materials that ranged from lean clays to sandy, lean clays to fat clays to sandy, fat clays; (2) a near-surface zone of clays of generally high plasticity; (3) an intermediate zone composed of sandy, lean clays of moderate plasticity; (4) a deep zone consisting of very clayey sands of moderate plasticity that was encountered in two (2) of the deep borings drilled at the site; and (5) a basal zone consisting of clays of high plasticity. A very general description of these five (5) stratigraphic zones is presented in the following separate sub-sections of this report. Surficial Zone. The soils of the surficial zone generally extended from the existing ground surface to depths of approximately 2 to 4 feet. The surficial zone materials were extremely variable and consisted of both fill soils and natural soils. The types of soils present in the surficial zone ranged from lean clays to sandy, lean clays of moderate plasticity to fat clays to sandy, fat clays of high plasticity. The soils of the surficial zone were typically brown to dark brown in color but were also mottled gray and brown, to dark gray to grayish-tan, to reddish-brown at some of the boring locations. The laboratory classification tests performed on samples of the clays collected from the surficial zone indicated a percentage of fines ranging from 62.9 to 76.8 percent. Since fines are described as siltand clay-sized particles, the percentage of the soil sample that was not characterized as fines represents sands and gravels, and typically only sands. Therefore, the percentage of sands within the surficial zone clays was calculated to be relatively high and to range from 23.2 percent (100 percent total 76.8 percent fines = 23.2 percent sands) to 37.1 percent (100 percent total 62.9 percent fines = 37.1 percent sands). The laboratory testing program indicated moderate to high Atterberg limit values with LL values ranging from 48 to 72 and corresponding PI values ranging from 29 to 49. Based upon the results of the laboratory classification tests, the soils of the surficial zone classified as either CL or CH type soils, i.e., 13

19 as clays of low to high plasticity, under the current USCS and as CM to CH type soils, i.e., clays of moderate to high plasticity, under the originally proposed USCS. The consistency, i.e., the strength categorization, of the clays was estimated from the results of the unconfined compression test and the pocket penetrometer tests to also be variable and to range from firm to very stiff. Near-Surface Zone. The near-surface zone consists of sandy, lean clays of variable thickness and was present at three (3) of the four (4) borings located in the general area of the building (borings B-1, B- 2 and B-4). The near-surface zone extended from approximately 2 or 4 feet depth to depths varying from 6 to 12 feet below the existing ground surface at the various boring locations. The soils of the nearsurface zone were typically tan to grayish-tan in color but were also brown to dark brown at one boring location. The results of the laboratory performed classification tests indicated that the clay soils of the near-surface zone exhibited percentages of fines ranging from 51.5 to 62.7 percent, which corresponded to a very high percentage of sands ranging from 37.3 to 48.5 percent. The results of the Atterberg limit tests conducted as part of the laboratory classification study indicated that the LL values ranged from 38 to 49 and that the corresponding PI values ranged from 21 to 30. The soils therefore classified as either CL type soils, i.e., as clays of low plasticity, under the current USCS, or as CM type soils, i.e., as clays of moderate plasticity, under the originally proposed USCS. The results of the pocket penetrometer tests indicated that the consistency of the clays of the near-surface zone ranged from stiff to very stiff. Intermediate Zone. The intermediate zone extended from below the bottom of either the surficial zone (boring B-3) or the near-surface zone (borings B-1, B-2 and B-4) to depths varying from 16 to 31 feet below the existing ground surface at the boring locations. The soils of the intermediate zone and consisted of clay that were generally tan to dark tan to grayish-tan in color but were also dark tan to brown to tannish-gray to grayish-brown to dark grayish-tan at some of the boring locations. The results of the laboratory performed classification tests indicated that the soils of the intermediate zone exhibited percentages of fines over a wide range of from 68.2 to 98.7 percent, which corresponded to a wide percentage of sands ranging from 1.3 to 31.8 percent. The laboratory determined LL values of the tested samples ranged from 52 to 89 and will corresponding PI values that ranged from 33 to 64. The soils of the intermediate zone therefore classified as CH type soils, i.e., clays of high plasticity, under both the current USCS and the originally proposed USCS. The consistencies of the clays of the intermediate zone were estimated from the results of the unconfined compression tests and the pocket penetrometer tests to range from stiff to very stiff. Deep Zone. The soils of the deep or basal zone extended were present at the two (2) deeper boring locations on the site (borings B-1 and B-4) and consisted of very clayey sands that ranged in color 14

20 from dark gray to grayish-tan. The soils of the deep zone extended between 31 and 37 feet below the ground surface at the boring B-1 location and between 17 and 27 feet depth at the boring B-4 location. The laboratory tests performed on the soil samples recovered from the deep zone indicated that the percentage of fines in the tested soil sample ranged from 35.7 to 49.7 percent. A significant percentage of the fines within the sands consisted of clays as evidenced by the moderate LL values of 47 to 53 measured in the laboratory testing program and the corresponding PI values that ranged from 28 to 33. The granular soils therefore classified as SC type soils, i.e., as clayey sands, under both the current and the originally proposed USCS. The relative density of the sands was estimated from the results of the unconfined compression tests and the pocket penetrometer test to range from medium dense to dense. Basal Zone. The soils of the basal zone were present from immediately below the deep zone at the locations of borings B-1 and B-4 and extended to the maximum exploration depths of 40 to 50 feet at the referenced boring locations. The soils of the basal zone consisted of clays of high plasticity that ranged in color from dark gray to dark grayish-brown, to dark brownish-gray. The laboratory classification tests performed on the samples of soils recovered from the basal zone indicated that percentages of fines ranged from 99.3 to percent. Therefore, the clays contained very little percentages of sand. The laboratory classification tests also indicated that the LL values ranged from 63 to 68 and that the corresponding PI values range from 42 to 46. The soils therefore classified as CH type soils, i.e., as clays of high plasticity, under both the current and the originally proposed USCS. The consistency of the clays of the basal zone was estimated from the results of the unconfined compression test and the hand or pocket penetrometer tests to range from very stiff to hard Limitations of Generalized Descriptions of Subsurface Stratigraphy at Boring Locations The previously presented generalized stratigraphical descriptions were utilized in the general foundation analysis as described in subsequent sections of this report. It should be recognized that the borings that were performed as part of the present field study were widely spaced and that there will likely be some changes in the generalized stratigraphy between the boring locations at the site. If variations from the previously presented or subsequently developed generalized descriptions of the subsurface stratigraphy are encountered during construction, CSC should be contacted in order to evaluate the potential effect of the variation on the recommendations presented in this report or in the subsequent prepared final report and to determine if some adjustments in our foundation recommendations are warranted by the variations in subsurface conditions. 15

21 4.3 GROUND WATER LEVEL OBSERVATIONS As previously described, water level observations were made during the initial dry auger drilling of the boring to determine the depths at which ground water appeared to be first seeping into the open boreholes. Ground water was observed to be seeping into the boreholes at depths ranging from 20 to 25 feet below the existing ground surface elevation at the boring locations. Based upon the ground surface elevations estimated from the topographic survey information provided by Jones & Carter, Inc. for the various boring locations, the corresponding elevations at which ground water was observed to be seeping into the boreholes was estimated to range from approximately EL to EL The boreholes were subsequently filled with soil cuttings following completion of the drilling operations as a safety measure for pedestrians crossing the project site. Therefore, longer-term ground water readings could not be obtained for the project. It should be understood that ground water information determined during this study was obtained to evaluate potential impacts on construction activities and should not be considered a comprehensive assessment of ground water conditions at the site. As previously discussed, granular strata consisting of clayey sands were encountered within the stratigraphy at the two (2) deeper boring locations on the site. In addition, several of the clay formations within the stratigraphy contained pockets and seams of sands. Sand formations and seams are typical of water bearing zones that can hold and/or transmit ground water. Consequently, it is possible that some ground water could be encountered in the sand formations and potentially also within the sand seams of the clay formations of the stratigraphy at the time of construction, especially if some of the climatological conditions favorable to ground water development are present as discussed in the following paragraph. It is important to recognize that ground water elevations may vary seasonally and that the absence of ground water at the time of the field study does not mean that ground water will not be present at the time of construction. Ground water elevations at any site are known to fluctuate with time and are dependent upon numerous factors. Ground water levels can be affected by such factors as the following, among others: (1) the amount of precipitation in the immediate vicinity of the project site and in the regional ground water recharge area; (2) the amount of infiltration of precipitation through the surface and near-surface soils; (3) the degree of evapotranspiration from surface vegetation at the project site; (4) the water level in adjacent drainageways or channels; and (5) the final grading and drainage scheme established for the project site both during the construction period and following construction. The amount of precipitation that occurs at or immediately before the time of construction is especially important. Therefore, as already noted, ground water levels at the time of the field investigation may vary 16

22 from the levels encountered both during the construction phase of the project and during the design life of the structures. If the long-term variation of the ground water level is critical to some design aspect of the proposed development, an extended hydrogeologic study involving the installation and long-term observation of piezometers should be undertaken to better define the pertinent ground water conditions at the site that may influence the design. 17

23 5.0 GENERAL ANALYSIS AND RECOMMENDATIONS 5.1 GENERAL CONSIDERATIONS The primary considerations in the design of a safe and economical foundation system for a structure are the following: (1) shear strength of the foundation soils and related bearing capacity of the foundation elements; (2) the compressibility characteristics of the foundation soils and the related settlement of the foundation elements; and (3) the volumetric stability or anticipated shrink-swell movements of the subsurface formations. In general, the strength and compressibility characteristics of the soils in the deeper formations at the site appeared to be adequate to provide bearing support of the loads associated with a typical five-story motel structure foundation system without excessive settlements. However, several zones of the soils within the upper portion of the stratigraphy at the boring locations contained clays of moderate to high plasticity. The potential volumetric stability and associated potential for shrink-swell movements of clay foundation soils in this geographical region must also be considered in the design of any motel-type structure foundation system as discussed in the following sections of this report. 5.2 GENERAL CONSIDERATIONS OF SHRINK-SWELL MOVEMENTS OF SOILS AND INFLUENCE ON FOUNDATION SYSTEMS As previously indicated, the soils within the upper portions of the stratigraphy at the boring locations across the site of the proposed motel building included clays of moderate to high plasticity. These moderate to high plasticity soils have the potential to experience significant volumetric changes (i.e., shrink-swell movements) with even minor variations in soil moisture content. The variations in soil moisture content that produce the shrink-swell movements are assumed to occur within a depth range below the ground surface known as the zone of seasonal moisture change. Although the extent of this zone of seasonal moisture change can vary with several factors, the depth of moisture variation in the geographical region of the project site is typically assumed to be in the order of 8 to 10 feet. Consequently, the greater the thickness of moderate to high plasticity clays within the zone of seasonal moisture change, i.e., in the upper 10 feet of the stratigraphy, the greater will be the potential magnitudes of shrink-swell movements. Conversely, in those areas of a site where low plasticity soils are present in significant thicknesses within the zone of seasonal moisture change, the potential movements will be lower. As previously indicated, the volume changes are typically caused by fluctuations in the moisture contents of the surficial, near-surface, and intermediate soil zones. Moisture changes can be induced by 18

24 natural causes, such as heavy seasonal precipitation or prolonged periods of drought. Vegetation and especially the root systems of large trees can also produce significant moisture variations, particularly between the drier summer months and the wetter spring and fall seasons. Pronounced changes in moisture content can also result from the presence of a building and such related activities as broken utility lines, landscape irrigating, or a poor storm water drainage system. In addition, some long-term increases in the moisture content of the building subgrade soils can be expected due to the sealing off of the subgrade by the floor slab which minimizes the natural loss of soil moisture by evaporation. High plasticity clays, such as those existing at the subject site, can experience shrink-swell movements of significant magnitudes with even minor variations in moisture content. Consequently, some movements should be expected for either a shallow foundation system element founded within a stratigraphy composed of these clays or for any floor system founded on top of these clays. The shrink-swell movements that could occur may produce deflections and differential movements in a building foundation system and superstructure, which, if not accounted for in the design phase of the project, could result in distress to the structures in the form of cracking of exterior masonry walls and interior dry walls, or cracking or deformation of a building slab. Shrink-swell movements of large magnitudes can even cause instability of the structure. 5.3 MAGNITUDES OF POTENTIAL SHRINK-SWELL MOVEMENTS Calculation of Magnitudes of Potential Total Shrink-Swell Movements for Existing Soils Stratigraphy Calculations were performed to estimate the magnitudes of total shrink-swell movements based upon an idealized subsurface stratigraphy formulated based upon the soils present at the various boring locations across the proposed building area. The magnitudes of the shrink-swell movements are sometimes referred to as the potential vertical rise (PVR). The calculations were based upon the following factors, among others: (1) the plasticities of the existing soils within the various strata comprising the idealized stratigraphy; (2) the existing moisture contents of the soils; (3) the potential future changes in moisture content assuming that efforts will be made to control the moisture regime in the building areas as subsequently recommended; and (4) the existing overburden pressures of the stratigraphy at the project site based upon the following discussed assumptions. The topographic survey information provided by Jones & Carter, Inc. indicates that existing surface grades across the area of the proposed building appear to range from approximately EL 329 to EL In addition, we understand that the proposed finished floor elevation of the building will be at EL 328, and that the slab subgrade elevation will be approximately EL (assuming a 6 inches or 0.5 feet thick slab). Therefore, we have assumed that approximately 1.5 feet to 3.1 feet of existing soils will be excavated from the proposed building area to 19

25 reach of the proposed slab subgrade elevation (existing grades of EL and EL 329 minus proposed slab subgrade EL = 3.1 feet and 1.5 feet) and that no fill may be added to create the proposed building pad. The calculations performed for the present study were based upon a modified procedure developed by McDowell as outlined in Texas Department of Transportation (TxDOT) Test Method TEX- 124-E. Calculations were performed based upon an idealized stratigraphy developed from the soils encountered at the various boring locations across the site. Based upon an idealized subsurface stratigraphy that was developed from the soils present at the boring locations in the proposed building area, total PVRs in the range of 2.8 to 3.0 inches were computed for the existing soils at the site. It should be recognized that the actual magnitudes of shrinking and swelling movements may be even greater that the predicted PVR values of soils with greater potential for volumetric movement are present in areas of the site other than at the boring locations and if moisture conditions in the proposed building area are not controlled either during or following construction. The computed range in PVR values is considered to be high. The major portion of this potential shrink-swell movement is attributable to the moderate to high plasticity clays present in the upper portion of the stratigraphy at all of the boring locations drilled in the building area on the site. As discussed in the subsequent subsection of this report, the magnitude of the potential movements can be reduced if some of the existing high plasticity clays are excavated from the stratigraphy across the areas of the proposed building locations and are replaced with compacted select fill soils with a lower potential for movement Reduction in Magnitudes of Potential Shrink-Swell Movements through the Excavation and Replacement Scheme A site development procedure referred to as the excavation and replacement scheme could be employed to significantly reduce the magnitude of potential volumetric movements of the foundation soils. The excavation and replacement scheme involves the excavation or removal of some or all of the surficial, near-surface and intermediate zone strata of moderate to high plasticity clays and the replacement of the existing soils with select fill soils composed of materials with a potential for low magnitudes of shrink-swell movements. The material and placement requirements for the select fill used to construct the building pad and general recommendations concerning construction of the building pad are outlined in Section 10 of this report. The degree to which the calculated potential shrink-swell movements could be reduced by the excavation and replacement scheme would depend upon the depth of the excavation of the existing soils and the corresponding replacement with select fill soils. Based upon the idealized stratigraphy developed 20

26 from the soils present at the various boring locations across the site, computations were performed to determine the corresponding reduction in calculated shrink-swell movements with each 2-foot layer of the existing soils that is removed and replaced with select fill soils. The results of those calculations for total shrink-swell movements are presented in Table 1 Calculated Potential Total Vertical Movements for Various Depths of Excavation of Existing Soils and Replacement with Select Fill Soils. It should be recognized that the magnitudes of total PVRs presented in the table may be exceeded if soils with greater potential for shrink-swell movement are present in areas of the site other than at the boring locations and if moisture conditions in the proposed building area are not controlled either during or following construction. Table 1. Calculated Potential Total Vertical Movements for Various Depths of Excavation of Existing Soils and Replacement with Select Fill Soils Depth of Excavation of Existing Soils and Replacement with Select Fill Soils (feet) Range in Potential Vertical Movements Due to Shrinking or Swelling of the Foundation Soils (inches) Comments or Remarks to 3.0 inches Existing soils in present condition to 1.9 inches Excavation and replacement of existing surficial zone soils that consist of clays of moderate to high plasticity at the boring locations will produce a significant reduction in the total PVR to 1.2 inches Excavation and replacement of additional thicknesses of clays of moderate to high plasticity will produce even greater magnitudes of reduction in the potential total PVR to 1.0 inches Even greater depths of excavation and replacement of the moderate to high plasticity clays of the upper portion of the stratigraphy will produce even more reductions in the total PVR to 0.6 inches Deeper depths of excavation and replacement of the moderate to high plasticity clays within the upper portion of the stratigraphy will produce additional reductions in the total PVR. Note: 1. The magnitudes of total PVRs presented in the table may be exceeded if soils with greater potential for shrink-swell movement are present in areas of the site other than at the boring locations and if moisture conditions in the proposed building area are not controlled either during or following construction. As can be seen from a review of Table 1, the magnitude of potential vertical movements due to shrinking or swelling of the foundation soils will depend upon the selected depth for excavation and 21

27 replacement. In general, the greater the depth of excavation and replacement, the greater will be the reduction in potential vertical movement General Building Pad Design and Construction Techniques If the excavation and replacement option is utilized at the site, we recommend that the excavation for the building pad should be planned to ensure that the completed building pad is of uniform thickness, even if the ground surface slopes across the building areas as depicted in the following Plate 1 Schematic Illustration of Excavation of Existing Soils and Replacement with Select Fill Soils to Create Building Pad on Sloping Ground Surface. Since the existing ground surface has a slight slope across the proposed building location, deeper excavations along the up-slope portion of the pad may be required in order to achieve a building pad of uniform thickness. Otherwise, the thickness of fill materials in the building pad area will be variable and could increase potential differential foundation movements. Additional recommendations concerning construction of the building pad are presented in Section 10 of this report. Any fill added to the site to construct the building pad for the proposed building should consist of a structural fill with a potential for low magnitudes of shrink-swell movement and which conforms to the requirements and placement procedures for select fill as outlined in Section 10.4 of this report. 22

28 Plate 1. Schematic Illustration of Excavation of Existing Soils and Replacement with Select Fill Soils to Create Building Pad on Sloping Ground Surface 23

29

30 5.4 TYPES OF FOUNDATION SYSTEMS CONSIDERED The range of potential total vertical movements previously presented in Table 1 is significant and should be considered in the design of the foundation system for the proposed structure. Accordingly, consideration was given to foundation systems that would minimize the potential detrimental effects of such movements. The different types of foundations considered for the proposed structure at the subject site are listed below and are also illustrated on the accompanying Plate 2 Types of Foundation Systems Considered. Each type of foundation system is discussed in the following sections of this report. 1. Drilled pier and structurally suspended floor system (Type I, Plate 2) 2. Drilled pier with subgrade-supported floor system (Type II, Plate 2) 3. Shallow stiffened slab-on-grade foundation system supported on subgrade of either natural soils or select fill soils (Type III, Plate 2) The foundation systems are generally listed above in order of increasing risk of unsatisfactory performance and decreasing cost of design/construction. For example, the first foundation system has the lowest performance risk, but it also probably represents the most costly foundation system to construct. Conversely, the last foundation system in the list has the greatest risk with respect to unsatisfactory performance, but is also generally the least expensive type of foundation system to construct. The owners and designer should review the different types of foundation systems and select the type of system that is most compatible with the owners and designer s performance expectations for the structure, as well as the project construction budget that is established by the owner. The expectation of structural performance should include a consideration of the degree of risk of cracking or distress to the structure that can be accepted with the various types of foundation systems Advantages and Disadvantages of the Various Types of Foundation Systems Drilled Pier and Structural Floor Slab Foundation System (Type I, Plate 2). The most affirmative means of support for structures located at sites with stratigraphies composed, at least in part, of soils with significant shrink-swell potential would be a foundation system composed of deep drilled piers with a structural floor system (Type I, Plate 2). The main superstructure loads are supported by drilled piers that penetrate the upper, potentially volumetrically active soil strata and are founded in the deeper, stable soil strata below the zone of seasonal moisture change. The piers are typically constructed with a widened base, called a bell or underream, to provide an anchor for the bottom of the pier against potential uplift forces along the upper portion of the pier. 24

31 Plate 2. Types of Foundation Systems Considered 25

32

33 A structural floor system is employed in conjunction with the piers. The structural floor system is typically supported by the piers and suspended over a crawl space or void space, thus freeing the floor from contact with the potentially volumetrically active soils that could produce distress in the floor system. Drilled Pier and Subgrade-Supported Floor Slab Foundation System (Type II, Plate 2). Although a structurally suspended slab system is the most affirmative means to support the floor loads of a building while minimizing the potential detrimental effects of expansive soils, considerations of initial construction economy by the owners will sometimes discourage the use of a structural floor system and lead the owners to consider other foundation systems. One other type of foundation system that is used in combination with drilled piers is a subgradesupported floor slab system (Type II, Plate 2). A Type II foundation system uses the drilled pier foundation elements to support the exterior wall loads and all column loads but will employ a subgradesupported floor slab system in which the slab is supported directly on a thick pad of select fill soils. The Type II foundation system has several variations, with one involving the use of structural grade beams for movement-sensitive exterior masonry walls and the use of a structural floor system for interior portions of the building that have movement-sensitive floor coverings, such as ceramic tile in restrooms or marble tile in entryways. The structural grade beams and structural floor systems should only be used if the void space beneath the exterior structural grade beams or interior structural floor system can be drained effectively. Otherwise, the beams and slab will have to be supported directly on select fill soils and designed for anticipated movements and uplift pressures. Although it should be recognized there is always the risk of foundation movement and related distress with a subgrade-supported slab system, some success has been achieved with such systems in this area when the slab is supported on a thick pad of select, volumetrically stable fill soils for which the material properties and placement procedures are controlled. A zone of the existing volumetrically unstable soils is typically excavated to a significant depth, and the excavated soils are replaced with more volumetrically stable select fill soils as part of the pad construction. Also, care is taken in the development of the site plans to ensure that the building pad is elevated significantly above the surrounding ground surface to discourage the collection of moisture at the building location. Site development plans will also incorporate features that are part of a deliberate and concerted effort to control moisture conditions around the building. As part of that control effort, the landscaping plans for the development are formulated so that water is not introduced in the foundation soils immediately surrounding the building. Finally, relatively impermeable pavement or sidewalks or soil cover layers are constructed up to and around the building to serve as horizontal moisture barriers. 26

34 Shallow Slab-on-Grade System. Another type of foundation system that is sometimes considered is a shallow foundation system that is referred to as a slab-on-grade foundation (Type III, Plate 2). This type of foundation system has foundation elements composed of grade beams and spread footings or widened portions of the grade beams that transfer the major structural loads to the soils in the upper portion of the stratigraphy. The floor system is entirely subgrade supported. However, we understand that a shallow slab-on-grade foundation system (Type III, Plate 2) is not being considered for the proposed five-story building and therefore, such a foundation system is discussed only briefly in the following sections of this report and not specific foundation design values are presented in the remaining sections of the report for this type of foundation system. 5.5 RECOMMENDED TYPE OF FOUNDATION In recommending the type of foundation system to be employed for the proposed building, we have considered the following features of the site and the stratigraphy in the building area: The existence of previous structures and associated utilities at the site and the possible remnants of those features in the area of the proposed motel building. The variable ground surface elevations across the area of the proposed building including the steep change in grade of approximately 5 feet near the northeastern end of the proposed building location. The variability in the types of soils present in the surficial and near-surface zones at the boring locations across the proposed building area of the site; The moderate to high plasticity of the clays present within the surficial, near-surface, and intermediate zones of the stratigraphy at the site of the proposed building; and The very dry condition of many of the foundation soils of moderate to high plasticity at the time of the field study and the corresponding increased risk of swelling of the soils due to an increase in moisture content. Based upon our evaluation of the above-mentioned items, we recommend that a drilled pier foundation system with a structural floor slab system be utilized (Type I, Plate 2) as the foundation system for the proposed building. The drilled pier and structural floor system would provide the most affirmative means of support for the proposed building while minimizing the potential of distress to the building foundation system, the floor system, and the superstructure. If the costs of constructing the drilled pier-structural floor system cannot be accommodated within the project budget, then a combination drilled pier and subgrade-supported floor system (Type II, Plate 2) can be considered, provided that the risk of some distress to the floor system can be accepted by the owners in return for the lower construction costs associated with the subgrade-supported slab. The subgrade-supported slab will perform more successfully if a significant thickness of the existing moderate to high plasticity soils at the site are excavated and replaced with select fill soils as part of the proposed building pad construction. In addition, the subgrade-supported slab will have to be designed considering 27

35 several factors that are subsequently outlined in Sections 7 and 9 of this report. One of those factors involves the creation and implementation of a drainage plan that will assure the control of moisture in the building area. If it will not be possible to assure control of moisture in the proposed building area following construction of the proposed building, then the use of a subgrade-supported floor slab system should not be considered for the proposed building. Design values for each type of foundation system being considered for the proposed building are presented in the following sections of this report. 28

36 6.0 SPECIFIC FOUNDATION RECOMMENDATIONS DRILLED PIER AND STRUCTURAL FLOOR FOUNDATION SYSTEM (TYPE I FOUNDATION SYSTEM) 6.1 GENERAL As previously indicated, the most affirmative means of support for the proposed building at the subject site would be to use a combination drilled pier foundation and structural floor system. A brief discussion of recommended design values for the foundation elements that comprise this type of foundation system is presented in the following paragraphs. 6.2 DRILLED AND UNDERREAMED PIER FOUNDATIONS Design of Drilled and Underreamed Piers Founding Depth and Founding Formations Positive support of the structural loads of the proposed structures can be obtained by using isolated drilled and underreamed piers. The drilled piers should be founded at a depth of 20 feet below the surface grade existing at the boring locations at the time of the field study. Based upon the subsurface stratigraphy encountered at the three (3) boring locations within the building area (borings B- 1, B-2 and B-3), the soils at the 20-foot founding depth will likely consist of stiff to very stiff, fat clays that vary in color from dark tan to tannish-brown, to dark tan to brown. Deeper founding depths for drilled pier foundation elements could be considered. However, it is likely that pier excavations that penetrate the very clayey sands of the deep zone will have to be cased during construction to maintain the stability of the pier excavation, and this requirement for casing would add to the construction cost of the foundation. Therefore, recommendations for alternate founding depths for the piers are not presented in this report but could be considered if necessary Design of Drilled and Underreamed Piers Allowable Bearing Pressures We recommend that the bottoms of the piers be proportioned based upon the unit net allowable bearing pressures presented in the following Table 2 - Recommended Unit Net Allowable Bearing Pressures for Pier Foundation Elements. Unit net allowable bearing pressures are presented for the following two (2) indicated loading conditions: (1) maximum or total loading; and (2) sustained or continuous loading. The maximum load condition refers to the combination of dead load and other loads (live load, wind load, seismic load, thermal load, etc.) that produces the highest total or maximum loading of the pier. The sustained or continuous load condition refers to the combination of dead load with 29

37 continuously applied or sustained live load that the pier will have to support on a regular or continuous basis. Most settlement computations are based on the magnitudes of continuous or sustained loading. Pier base dimensioning for exterior bearing wall loads or for interior column loads should be in accordance with the unit net allowable bearing values corresponding to the more severe loading condition. The recommended net allowable unit bearing values incorporate the indicated factors of safety with respect to the theoretical ultimate bearing capacity. Table 2. Recommended Unit Net Allowable Bearing Pressures for Pier Foundation Elements FOUND- ING DEPTH, feet Note 1 DESCRIPTION OF FOUNDING FORMATION RECOM- MENDED MAXIMUM RATIO OF PIER BELL DIAMETER TO PIER SHAFT DIAMETER RECOMMENDED NET ALLOWABLE BEARING PRESSURE, Note 2 pounds per square foot Maximum or Total Loading Factor of Safety of 2 Sustained or Continuous Loading Factor of Safety of 3 20 feet Stiff to very stiff, fat CLAYS that vary in color from dark tan to tannish-brown to dark tan to brown. 3:1 13,500 psf 9,000 psf Notes: 1. Depth below ground surface elevation existing across proposed building area at the time of the field study. 2. Recommended allowable bearing pressures were rounded to the nearest 50 pounds per square foot (psf) Design of Drilled and Underreamed Piers Positive Skin Friction Positive skin friction may be considered for computing pier resistance to axial loading for pier shafts. However, some portions of the pier shaft may lie within two non-contributing zones where experience has shown that side resistance is not always developed. One non-contributing zone extends from the ground surface to near the bottom of the zone of seasonal moisture change. Research has shown that this upper non-contributory zone extends from the ground surface to a depth of approximately 8 to 10 feet below the ground surface. The reason for this upper non-contributing zone at the top of the pier shaft is due to the possible shrinking or drying of the clay soils in the surficial or near-surface zones away from the sides the pier, thereby breaking the contact between pier and soil that is necessary to develop side resistance. A second lower non-contributing zone exists for piers founded in cohesive soils, i.e., clay formations, but not granular formations. This lower non-contributory zone extends for a distance 30

38 corresponding to one (1) pier shaft diameter above the top of the bell. The reason for this lower noncontributing zone at the bottom of the pier is the documented build-up of moisture in the pier shaft along the bottom segment of the straight shaft piers and in the zone immediately above the top of the underream or bell. This accumulation of moisture in the foundation soils tends to produce weakening of the soils along the sides of the shaft and a consequent reduction in adhesion or side resistance. We recommend that the allowable unit skin friction or adhesion values listed in the following Table 3 - Recommended Allowable Unit Side Resistance (Skin Friction or Adhesion) Values for Pier Foundation Elements be considered for the portions of the pier shaft between the two referenced noncontributory zones. The recommended allowable values assume that the piers will be constructed using dry construction techniques, i.e., without the use of drilling fluids in conjunction with casing to stabilize the pier excavation. The recommended allowable values incorporate a minimum factor of safety of 2 with respect to the theoretical ultimate value. Table 3. Recommended Allowable Unit Side Resistance (Skin Friction or Adhesion) Values for Pier Foundation Elements RECOMMENDED DESCRIPTION ALLOWABLE DEPTH RANGE Note 1 OF SOIL UNIT SKIN FRICTION FORMATIONS ALONG SIDES OF PIER OR SHAFTS ADHESION Note 2 feet Stratum Description pounds per square foot Note 3 0 to 8 ft Upper non-contributing zone. 0 psf 8 to 20 ft Note 4 Stiff to very stiff, fat clays or sandy, fat clays that range in color from tan to dark tan, to dark tan to brown, to grayish-tan, to grayish-brown, to tannishgray, to dark grayish-tan. 400 psf Notes: 1. Depth below existing surface grade. 2. Incorporates a Factor of Safety of at least Value rounded to the nearest 100 psf. 4. For piers founded in cohesive soil (clay) stratigraphies, the bottom portion of the pier will not contribute to side resistance. The non-contributing zone shall extend a distance equal to one shaft diameter above the top of the bell and shall also include the entire depth of any bell or underream Design of Drilled and Underreamed Piers Pier Settlement We anticipate that total settlement of individual piers under the expected magnitudes of sustained loading will be relatively small. We estimate that maximum total settlement of the pier under the anticipated magnitudes of sustained loading will be in the range of 1 inch or less. Due to the cohesive 31

39 nature of the founding soils, the predicted settlements will likely occur over a relatively long-term time period as the continuous building loads are applied to the piers and the foundation soils consolidate under the applied loads. We anticipate that the differential settlement between adjacent pier locations will be as much as 75 percent of the total pier settlement. The pier foundation system and building superstructure framing system should be designed to accommodate the anticipated magnitudes of total and differential settlements Design of Drilled and Underreamed Piers Upward Acting Tensile Forces on Pier Tensile steel reinforcement will be required in the pier shafts to resist uplift forces acting on the pier foundation elements. Uplift forces may potentially be generated by external building loading such as from wind. Alternately, uplift forces may be generated by foundation soil loading conditions associated with swelling of the near-surface and intermediate zone clays around the upper portion of the pier shafts. The magnitude of the tensile forces in the pier shafts due to external building loading is not known at the present time. However, the uplift or tensile forces that may potentially be generated by swelling of the near-surface zone or intermediate zone clay formations against the sides of the pier shaft within the upper portion of the stratigraphy at the site can be calculated. The magnitude of the vertical uplift force due to swelling of the near-surface or intermediate zone soils can be determined by assuming that a soil-to-pier adhesion value of 2,000 psf is acting in an upward direction along the sides of the pier shafts within the upper 8 feet of stratigraphy at the site. The uplift force thus calculated for the potentially swelling soils should be used in determining the minimum area of reinforcing steel required for the piers to resist the swelling forces of the foundation soils. However, a greater amount of steel reinforcing may be required to resist other externally applied loads. Therefore, the amount of reinforcing steel used for the pier shafts should be determined based upon the most critical of the several loading conditions Design of Drilled and Underreamed Piers Spacing of Shafts (In Consideration of Group Action) We anticipate that the piers supporting the bearing walls or column loads of the proposed structure will be widely spaced. If adjacent drilled piers that support the proposed structures are spaced too closely together, the piers may not function as individual foundation elements, but rather as a group. It is possible that the total capacity of piers acting as a group will be less than the summation of the capacities of the individual piers comprising the group. The reduction in the capacity of individual piers due to group action will depend upon several factors, including the geometry of the pier arrangement (i.e., the spacing between the base of the piers and the row or column arrangement of the piers), and the load 32

40 characteristics of the piers (i.e., are the piers primarily end bearing elements or friction shafts), among others. In general, the negative effects of group action may be reduced if a minimum distance is maintained between the outside diameters of the bases of the individual pier foundation elements. We recommend that a horizontal edge distance or spacing corresponding to at least three (3) times the diameter of the largest base of adjacent piers be maintained. Therefore, if a pier with a bell or underream diameter of 42 inches or 3.5 feet was located adjacent to a pier with a bell diameter of 4 feet, we recommend that a minimum horizontal separation of 12 feet (3 times 4 feet) be maintained between the outside edges or perimeters of the two bases. Otherwise, group action may have to be accounted for by reducing the allowable capacity of the individual piers. As previously stated, the percentage of reduction will be largely dependent upon the geometry of the pier foundation elements Design of Drilled and Underreamed Piers Construction Considerations The soils at the recommended pier founding depth are considered to be cohesive. Accordingly, we believe that a maximum bell-to-shaft diameter ratio of 3 may be utilized in the construction of the belled piers. The pier shaft diameter of any pier should be at least 18 inches in order to facilitate cleaning and inspection of the base of the pier during construction. It is important to realize that there is a potential for ground water conditions to influence construction activities associated with pier installation. Ground water was observed to be seeping into the geotechnical boreholes at depths of approximately 25 feet below the existing ground surface during drilling operations. Although the depth at which ground water was encountered during the drilling operations was below the recommended founding depth, there is a possibility that ground water will be encountered during installation of the piers, particularly within the sand seams present within the clay formations of the stratigraphy. The extent of ground water influence on pier installation will be dependent upon the subsurface stratigraphy at a particular pier location, and also upon the time of construction and antecedent moisture conditions. Accordingly, since we anticipate that a deep foundation system will be employed for the support of the proposed building, we recommend that consideration be given to the installation of a test pier on an outlying site element (e.g., canopy or porte-cochere column, light standard, utility poles, etc.) to identify appropriate installation techniques and the potential need for casing of the pier excavations. Without the installation of a test pier, the potential need for casing to seal off the pier excavations from ground water infiltration should be anticipated. In addition, we strongly recommend that no pier excavation be left open any longer than is absolutely necessary. If it is desired to minimize potential problems with pier installation, it is critical that 33

41 pier reinforcement be inserted into the excavation immediately after drilling is complete and that there be no delays in the placement of concrete into the open pier excavation. In no event should a pier excavation be left open (i.e., not filled with concrete) following termination of the construction operations each day or prior to any precipitation event. Typically, the shorter the period of time that a pier excavation remains open, the lower the possibility that problems with groundwater migration into the excavation or with caving of pier sidewalls will occur. Other recommendations concerning pier construction are presented in Section 10 of this report. 6.3 STRUCTURAL FLOOR SLAB SYSTEM The structurally suspended floor slab, which includes all exterior and interior grade beams, should be designed with a permanent void space of at least 4 inches between the soil and the bottom of the slab or beam in order to isolate these structural elements from the potentially expansive soils. The void space between the bottom of the slab and/or beams and the underlying subgrade soils may be created by using conventional wooden forms or metal forms. Alternately, 6-inch wax-coated carton forms can be placed beneath the bottoms of the slab or beams in order to create the void space. The carton forms should only be used if the beam concrete is poured soon after placement of the carton forms in the excavated beam trench, and only if the trench is not allowed to fill with water in the interim. The presence of water in the trench excavations can cause collapse of the cardboard carton forms. The carton forms should be sufficiently strong to withstand the weight of the concrete placed in the beams without collapsing. Suitable rigid protective shielding or bulkheads made of plastic or concrete should be installed along both the inside and outside faces of the grade beams to minimize sloughing of soils into the interior of the void space and thereby compromising the clear distance between the bottom of the beams and the underlying soils. Alternately, the floor system can be constructed of precast, reinforced concrete panels or planks spanning between structural grade beams with the surface of the slab being formed by the placement of a minimum 2-inch concrete topping across the surfaces of the panels. Still another alternative is to use a wood floor system that includes a system of wood trusses or joists and girders that are supported by the drilled piers. Regardless of the selected method of construction, a permanent void space of at least 6 inches should be maintained between the bottom of any floor system element and the underlying soils. Provisions should be made to effectively ventilate and also to drain the void space beneath the floor system. Typically, one or more drains are located in graded depressions in the subgrade soils that form the bottom of the void space. The subgrade soils can be stabilized with hydrated lime or a thin mud mat of lean concrete can be placed over the subgrade soils to create a more suitable working 34

42 surface during construction and to promote drainage of the void space following construction. The drain(s) across the base of the void space should be connected to a storm sewer system. The drainage system should preferably function by gravity flow. However, if necessary, a sump pump should be utilized to effectively drain the void space beneath the floor system. In addition, adequate vents should be provided around the perimeter of the void space to effectively ventilate the crawl space underlying the floor system and to prevent moisture vapor build-up within the space. 35

43 7.0 SPECIFIC FOUNDATION RECOMMENDATIONS - DRILLED PIER, SUPPORT OF GRADE BEAMS AND COLUMNS, WITH SUBGRADE- SUPPORTED FLOOR SLAB (TYPE II FOUNDATION SYSTEM) 7.1 GENERAL A combination drilled pier and subgrade-supported floor slab as illustrated by the Type II foundation on Plate 2 may also be considered for the proposed structures. A Type II foundation system would involve the utilization of drilled piers for support of load bearing walls and any isolated columns. Any exterior masonry walls and other movement-sensitive walls should be supported on structural grade beams spanning between the piers as previously recommended for the structural floor system, provided that the void space beneath the grade beams can be effectively drained of any water that may collect in the void space. Otherwise the grade beams would have to be supported in a thick select fill pad and would have to be designed for the magnitudes of movement and swelling pressure associated with the stratigraphy as modified by the select fill pad. The difference between the Type II and Type I foundation systems is that a subgrade-supported floor slab system is used with the Type II system in lieu of a structural slab, except in areas with movement-sensitive floor coverings, such as tile, wood planks, etc., where a structural floor system should still be considered. Provisions for draining the void spaces formed beneath the structural slab areas as previously discussed must also be provided. In summary and except for areas with movement-sensitive floor coverings, the building floor system in a Type II foundation will consist of a concrete slab supported directly on a prepared pad of volumetrically stable soils. The pad of volumetrically stable soils should be created by excavation of some of the existing highly plastic clays and replacement of those potentially volumetrically active soils with more stable select fill soils as previously discussed. The slab should also be stiffened and designed to accommodate potential total vertical movements and differential movements that may still occur even with the constructed pad. 7.2 PIER AND STRUCTURAL GRADE BEAM DESIGN VALUES The piers should be designed based upon the recommendations presented in Section 6 of this report. Structural grade beams may be used for support of movement-sensitive walls, such as exterior masonry walls. Recommendations concerning structural grade beams were also discussed in Section 6. Provisions should be made to drain the void space beneath the structural grade beams in case storm water accumulates beneath the beam. Otherwise, water that collects in the void space can migrate beneath the subgrade-supported slab areas and cause swelling of the foundation soils and movement of the floor slab. 36

44 If an effective drainage system for the void space beneath the grade beams cannot be established, then a Type II foundation system with void spaces beneath the grade beams should not be used. Rather, the grade beams should be supported directly on the select fill soils of a built-up building pad or on the existing foundation soils if adequate drainage of a void space cannot be provided. The subgradesupported grade beams and floor slab would therefore have to be designed to accommodate the potential vertical movements and swelling pressures associated with the stratigraphy as modified by the construction of the building pad. 7.3 SUBGRADE-SUPPORTED FLOOR SLAB SYSTEM Slab Grade Beams or Footing Founding Depth The grade beams for the subgrade-supported floor slab system will function as continuous footings. We anticipate that the slab will have both exterior and interior grade beams. The grade beams should be founded at a minimum depth of 3 feet below the finished floor elevation or approximately 2.5 feet below the finished ground surface surrounding the structure, assuming that the finished floor elevation will be approximately 6 inches above the surrounding ground surface. The nature of the foundation soils will depend upon the site grading operations associated with the building pad. If a thick pad of select fill soils is constructed, then the base of the footings would be founded in compacted, select fill soils. If a thick building pad of select fill soils is not constructed, then the footings would be founded in existing natural soils. The natural soils will likely consist of either stiff to very stiff, mottled gray and brown or grayish-tan, sandy, fat clays, or of stiff, brown, lean clays Footing Bearing Values We recommend that the bottom portions of the continuous footings or grade beams be proportioned based upon the unit net allowable bearing pressures presented in Table 4 Recommended Unit Net Allowable Bearing Pressures for Continuous Footing Foundation Elements Founded in Natural Soils or in Compacted Select Fill Soils. Recommended allowable bearing pressures are presented in Table 3 for footings founded in both existing natural soils and footings founded in a thick pad of compacted, select fill soils in which there is at least 2 feet of compacted select fill below the base of the footing. Unit net allowable bearing pressures are presented in Table 3 for the same two (2) loading conditions previously discussed in the report section for drilled piers. The bearing-capacity values presented in Table 4 were based upon the computed theoretical ultimate bearing capacity reduced by minimum factors of safety of 2 and 3, respectively, for the given design conditions. 37

45 Dimensioning of the base of the footings for exterior or interior bearing wall loads should be in accordance with the recommended net allowable unit bearing values corresponding to the more severe loading condition. The footings should have a minimum base width of 16 inches to minimize the potential for puncture-type shear failure of the foundation soils. Table 4. Recommended Unit Net Allowable Bearing Pressures for Continuous Footing Foundation Elements Founded in Natural Soils or in Compacted Select Fill Soils FOUND- ING DEPTH Note 1 DESCRIPTION OF FOUNDING SOIL FORMATION RECOMMENDED UNIT NET ALLOWABLE BEARING PRESSURES, Note 3 pounds per square foot (psf) Sustained or Maximum or Total Continuous Loading Loading Factor of Safety of 3 Factor of Safety of feet Compacted, select fill soils Note 2 2,800 psf 4,200 psf 2.5 feet Natural soils Varies from stiff to very stiff, mottled gray and brown or grayish-tan, sandy, fat clays, or of stiff, brown, lean clays 2,200 psf 3,300 psf Notes: 1. Depth below final surface grade. 2. Assumes minimum thickness of 1 foot of compacted, select fill soils below base of footing. 3. Recommended allowable bearing pressures were rounded to the nearest 100 pounds per square foot (psf) Potential Total and Differential Vertical Movements The subgrade-supported floor system will have to be stiffened and reinforced to minimize distress due to possible subgrade soil movements. The soil movements may be attributable to either shrinkswelling of the foundation soils or to consolidation of the foundation soils under applied structural loads. Magnitudes of total potential shrink-swell movements were presented in Table 1 of Section 5.3. The total magnitude of settlement of any subgrade-supported slab under the anticipated magnitudes of sustained floor loading should not exceed 1 inch. The potential movements presented in the preceding paragraphs for shrinking or swelling of the foundation soils or for settlement of the slab under applied structural loads represent total movements. The magnitude of the total vertical displacements may vary across the areas of the proposed motel building and will depend upon several factors, including the following, among others: (1) the subsurface stratigraphy at a particular location; (2) the existing moisture content of the subsurface materials at the 38

46 time of construction; (3) the magnitude and source of any changes of the moisture regime in the building areas during construction and following completion of construction; (4) the depth of removal of any existing soils at the site; (5) the final thickness and characteristics of new fill placed on the site; and (6) the magnitudes of sustained loading transmitted to the footings and the dimensions and founding depths of the footings. Due to these potential variations in subsurface and structural loading conditions across the areas of the proposed buildings, the potential differential movements of the foundations system may be as high as 75 percent of the predicted total movements. Due to the localized area of the potential variations, the differential movements could occur over horizontal distances as short as 5 to 10 feet. The potential differential movements should be considered in the design plans for the proposed motel building Building Pad Preparation Although there is always an inherent risk of movement of a subgrade-supported slab system, some success has been achieved with such systems in this area when the slab is supported on a thick pad of select, volumetrically stable fill soils, especially when the pad is constructed by excavating some of the existing moderate to high plasticity soils and replacing the native soils with select fill. Slab building pad and site preparation requirements are discussed in Section 10 of the report. The likelihood of success with a subgrade-supported slab system can be increased if the grading and drainage scheme for the site is formulated to control moisture conditions around the building as is also described in Section 10 of this report Architectural and Structural Element Detailing to Minimize Effects of Foundation Movement The effects of the potential shrink-swell movements of the subgrade soils on sensitive architectural and structural features of the proposed buildings should be considered in the design phase of the proposed structures. Some examples of such features are exterior entryways, exterior masonry walls, windows and door openings, interior block walls, or tiled floors. The superstructure and architectural elements of the proposed motel building should be designed to accommodate the predicted movements. For example, architectural elements that could exhibit distress, such as exterior stone or brick walls, should be avoided, if possible, and more flexible wood or metal exteriors or isolated masonry panels used in lieu of continuous masonry walls. If masonry walls have to be employed in a structure, there should be frequent jointing of the walls, especially around all doorways, windows, and other wall openings to allow for some potential movement without cracking of the masonry features at these weak points in the wall. In addition, long spans of masonry walls should be avoided without the incorporation of expansion joints at maximum horizontal spacings of 12 to 15 feet. 39

47 Similarly, jointing of interior dry walls above door and window openings and the use of slip joints between dry wall panels should be considered. Also, the creation of an air gap between the tops of interior non-load bearing walls and the overhead roof system has sometimes been employed to permit some movement of the floor slab without distressing the interior walls. Still another example of detailing to accommodate potential foundation movement involves movement-sensitive floor coverings, such as those containing ceramic tile, marble, or wood. Such movement-sensitive floor coverings should be avoided. If movement-sensitive floor coverings must be placed in the structures, we recommend that strong consideration be given to the use of geotextile reinforcement layers and/or underlayment layers between the floor coverings and the slab. Also, the tile should be frequently jointed so as to minimize the manifestation of distress cracking associated with slab movement. In addition, the slab may be freed from the surrounding grade beams and allowed to float or move independently of the pier supported floor or wall elements, provided that such movement is considered in the design of the building architectural features. If the slab is generally designed to be a floating slab that is not tied to the surrounding grade beams, it may have to be lightly doweled into exterior structural grade beams at doorway locations to minimize possible interference with door openings and closings that are sometimes associated with slab movement at doorway locations. Furthermore, the foundation system and supported superstructure should have some joints, especially along the lengths of the building where there are changes in building orientation, such as for L-shaped or T-shaped structures. Foundation stresses tend to be concentrated in such areas where there is a change in the alignment of the building footprint. Additional reinforcing steel should be added to the slab in such alignment change areas. The use of flexible plumbing connections for water and sewer piping can help reduce potential leakage frequently associated with slab movements. Similarly, the employment of through-slab sleeves for rigid electrical conduit can help to minimize distress to the electrical system. Furthermore, all drainage piping and general plumbing piping systems associated with the building or in proximity to the building should be leak tested following installation. Water produced from any leaks in drainage or pressure piping following construction could produce localized swelling movements in the foundation clays. The swelling movements may be of a greater magnitude than is typically associated with seasonal moisture variations. These increased swelling movements could result in distress to foundation elements, the building superstructure, and other site development features. 40

48 8.0 PAVEMENT RECOMMENDATIONS 8.1 GENERAL DESIGN CRITERIA USED FOR PAVEMENT ANALYSES The American Association of State Highway and Transportation Officials (AASHTO) design procedure was used to compute pavement thickness requirements for the paved areas, including the site access drive, the circulation lanes within the parking areas, and the parking space areas adjacent to the circulation lanes. The anticipated traffic loads and the load-carrying characteristics of the subgrade soils were used to determine required thicknesses for a rigid pavement section with a PCC surface course over a chemically-stabilized subgrade soil layer. Results of the laboratory testing program were used as inputs into the pavement analysis to represent the load-carrying capacity of the existing subgrade soils which are anticipated to be modified by chemical stabilization. The following sections present the design factors used in the analysis and also offer the resulting pavement design recommendations. 8.2 ANTICIPATED PROJECT TRAFFIC CONDITIONS AND VEHICLE CHARACTERISTICS As previously discussed, specific information concerning anticipated traffic patterns and vehicle loadings are not known for the proposed project at the time of this report. However, we have made certain assumptions based upon the number of parking spaces and the access drive and circulation lane scheme planned for the proposed project. We anticipate that the proposed paved access drives and circulation lanes will be used predominantly by light passenger vehicles, with occasional use by light to mediumweight supply and delivery trucks. The light to medium-weight delivery trucks are expected to mostly consist of two-axle, six-tire vehicles with gross vehicle weights (GVWs) of less than 24,000 pounds. Some heavy to very heavy trucks and other vehicles may also travel over the paved areas of the access drives and circulation lanes on an occasional or infrequent basis. The heavy truck traffic will be largely limited to occasional delivery trucks or solid waste collection trucks. The heavy-weight delivery trucks are expected to have three axles and 10 tires with a maximum GVW of approximately 46,000 pounds. The very heavy trucks are expected to include only emergency vehicles that will utilize the paved roadways on a very infrequent basis. The very heavy-weight emergency vehicles, such as fire trucks, are expected to have a maximum of six axles and a GVW of approximately 70,000 pounds. 41

49 8.3 SUBGRADE CLASSIFICATION Although specific grading plans for the paved areas have not been finalized, we do anticipate that all organic topsoils and all weak surficial soils will be stripped from the proposed paved areas across the site. Based upon the borings drilled across the proposed paved areas (borings B-5, B-6, B-7 and B-8), the subgrade soils beneath the organic topsoil in the proposed paved area are expected to predominantly consisted of clays of moderate to high plasticity with PI values of 20 or greater. It is possible that the subgrade soils in some areas of the site between the boring locations will consist of soils of low plasticity with high percentages of silts and fine sands. These surficial silty and sandy soils will exhibit poor load-bearing characteristics and will be difficult to process and compact if they contain high moisture contents at the time of construction, such as could occur after periods of heavy and/or prolonged precipitation. Silty and fine sandy soils that are underlain by clay formations have a tendency to trap rainwater and to pump when compacted, particularly when they are disturbed by heavy construction equipment which tends to promote the collection of water within the soils. Pumping refers to the condition when the energy applied during the compaction of the soils is transferred into the relatively incompressible water trapped within the void spaces of the soil structure and not to the soil skeletal structure. Thus, the compaction energy is absorbed by the water within the void spaces of the soil structure and not by the soil structure itself. As a result, the soil structure undergoes little or no densification under the applied energy of compaction. Rather, the compaction energy is transferred laterally within the water mass to produce a wave in the soils that resembles a water bed effect. Pumping soils provide extremely poor load support capacity for subgrade-supported paving systems. As a result, we recommend that if any surficial silty or fine sandy soils are encountered during grading operations, these soils should be stripped from the site. Therefore, deeper excavation depths than are normally employed to strip surficial topsoils may be required in some areas of the site to ensure the removal of all weak surficial soils. If any weak, silty and fine sandy surficial soils are not removed from the site and become wet and unstable, a ground-supported foundation slab and pavement sections could experience significant distress due to the weak and compressible character of these surficial soils. We anticipate that any filling of the paved areas of the site will be accomplished with general pavement area fill soils as discussed in Section 10.3 of this report. Therefore, it is likely that the pavement subgrade soils will consist of either natural clays of moderate to high plasticity or of imported fill soils of moderate plasticity. The addition and processing of chemical-stabilizing agents, such as hydrated lime, fly ash, and/or Portland cement into the subgrade soils can increase the strength and volumetric stability of the soils within the treated subgrade zone, especially with compaction of the chemically-altered soils. 42

50 Consequently, we strongly recommend that the subgrade soils be chemically stabilized. If the subgrade soils are not chemically stabilized, there may be a significant loss of subgrade support if the unstabilized soils become wet and saturated. Accordingly, we have assumed in our analysis that the subgrade soils will be chemically stabilized and compacted to a depth of at least 6 inches to improve the support capacity for the subgrade layer. As previously discussed, the chemical used to stabilize the subgrade soils will depend upon the nature of the subgrade soils. If the subgrade soils consist of clays, sandy clays, or clayey sands of moderate to high plasticity with a minimum PI value of 20, we recommend that the pavement subgrade be stabilized by the addition of hydrated lime. Details concerning material characteristics and placement procedures both for a lime-stabilized subgrade and for other types of stabilizing agents with different types of subgrade soils that may be encountered in limited areas of the site are presented in Section PAVEMENT THICKNESS REQUIREMENTS Pavement thickness calculations were performed for main access drive, the circulation lanes within the parking areas, and the parking space areas. The pavement calculations utilized the previously discussed traffic conditions, the previously indicated subgrade strength properties (assuming that the subgrade soils will be chemically stabilized and compacted to a minimum depth of 6 inches in accordance with the provisions of a subsequent section of this report), and assumed typical paving material strength properties and reliability factors. The required total pavement thicknesses were computed for a rigid pavement system for two categories of pavement use: (1) the access drives and the circulation lanes within the parking areas, which were categorized as medium-duty pavement sections; and (2) the parking space areas, which were characterized as light-duty pavement sections. The recommended pavement sections are presented in the following tables. The minimum thicknesses for the various layers of the rigid pavement section which are recommended for use in the access drive and the circulation lanes and any other medium-duty paved areas that will have to carry some medium-weight truck traffic on a regular basis, some heavy-weight delivery trucks on an occasional basis, and some very heavy-weight emergency vehicle truck traffic on an infrequent basis are presented in Table 5. 43

51 Table 5. Pavement Thickness Schedule for Conventionally Reinforced and Jointed PCC Access Drive and Circulation Lanes within Parking Areas (Medium-Duty Pavement Section) Thickness (in) Note 1 Material Description 6.0 Reinforced Portland cement concrete surface course Note Compacted chemically-stabilized subgrade soils Note Total constructed pavement thickness Notes: 1. The design section for entrances to adjoining property driveways and tie-ins to intersecting city and state roadways may differ from those presented in the table, and should be established based on applicable requirements. 2. Concrete assumed to have a minimum modulus of rupture (as determined in a third point beam loading test) corresponding to 650 psi (approximately equivalent to concrete with a 28-day compressive strength of 4,000 psi). 3. The requirements for compaction and chemical stabilization of the subgrade soils are presented in Section 10. If it is anticipated that the truck traffic will exceed the previously indicated volumes and vehicle weights, then the wearing surfaces of the rigid pavement section should be increased to 7 inches. The parking areas are not expected to have to carry truck traffic and therefore may be constructed with thinner pavement sections that are appropriate to light-duty paved areas. The computed pavement section thicknesses for the parking areas are presented in Table 6 for the rigid pavement system. Table 6. Pavement Thickness Schedule for Conventionally Reinforced and Jointed PCC in Parking Space Areas (Light-Duty Pavement Section) Thickness (in) Note 1 Material Description 5.0 Reinforced concrete surface course Note Compacted chemically-stabilized subgrade soils Note Total constructed pavement thickness Notes: 1. The design section for entrances to adjoining property driveways and tie-ins to intersecting city and state roadways may differ from those presented in the table, and should be established based on applicable requirements. 2. Concrete assumed to have a minimum modulus of rupture (as determined in a third point beam loading test) corresponding to 650 psi (approximately equivalent to concrete with a 28-day compressive strength of 4,000 psi). 3. The requirements for compaction and chemical stabilization of the subgrade soils are presented in Section 10. The reduced pavement sections for the parking space areas should only be used if heavy truck traffic is prohibited from using the parking areas. Use of the parking areas for turn-around maneuvers for medium to heavy trucks should not be permitted. Otherwise, even a few passes by heavy trucks over the thinner pavement sections may produce distress in the pavement section. If no safeguards, such as raised curbing or islands, painted striping, or signage, are employed to minimize the possibility that trucks will utilize the paved parking areas, then the heavy-duty pavement sections should be employed in the parking areas. 44

52 All of the recommended pavement sections represent minimum required thicknesses for the planned paved areas for the project. As indicated in the footnotes to the tables, tie-ins to existing streets or highways should be made in accordance with the sections presented in the previous tables or applicable city/state design criteria, whichever is more stringent. All of the concrete paving should be reinforced with steel reinforcing bars to minimize temperature and shrinkage cracking, to discourage widening of any cracks that may form, and to aid in transferring loads across joints. Adequate jointing of the concrete pavement should be included in the design and construction of the pavement system. Concrete pavement should be segmented by the use of control or contraction joints placed a recommended spacing of 12 feet center to center and a maximum spacing of 15 feet. Keyed and doweled longitudinal joints should be located in all roadway sections greater than one lane (10 to 13 feet) in width. Expansion and/or construction joints should be placed at a maximum spacing of 120-foot intervals. Expansion joints should not be placed through the middle of area inlet boxes in the pavement. Isolation joints should be placed between the pavement and all existing or permanent structures (such as retaining walls or drainage inlets). All joints should be sealed with Sonneborn Sonolastic SL1 (or equivalent) to minimize infiltration of surface water to the underlying subgrade soils. The edges or periphery of pavement sections are a natural weak point due to the lack of edge support beyond the paved area. Parallel cracks in the pavement section along the edge of many paved areas are a common indication of partial edge failure. Some provision for support of the edge of the paved areas should be included in the current design plans. The most common means of edge support is a PCC curb and gutter. In addition, we recommend that the exterior boundary of the chemically-stabilized subgrade layer extend at least 2 feet beyond the edge of the pavement surface layer. These extensions will help to minimize the formation of edge cracks in the pavement system due to either a lack of boundary support under wheel loading as previously discussed or due to shrinking of subgrade soils away from the outer edge of the pavement during dry weather and the subsequent loss of subgrade support. 8.5 PAVEMENT SYSTEM MAINTENANCE Pavement Drainage The control of surface and ground water is a critical factor in the performance of a pavement system. Adequate surface and subsurface drainage provisions should be included in the pavement design scheme. Drainage provisions may include the following, among other items: a steeply graded pavement surface to quickly transport storm water to collection or discharge points; an adequate number of storm water catch basins or curb inlets in the paved areas to capture the storm water; and adequately sized storm 45

53 water sewer piping. Finally, landscaping or green areas and other potential sources for moisture infiltration within the limits of the parking area should be minimized, if at all possible Pavement Maintenance The owner should institute and budget for a regular maintenance program for the paved areas. Regular pavement maintenance is a prerequisite for achieving acceptable performance levels over the anticipated life of the pavement system. Cracks occurring in the surface course of the pavement should be sealed as soon as they occur in order to minimize storm water infiltration into the underlying pavement system layers and subsequent degradation of performance. Sealants that can withstand exterior exposures, such as Sonneborn Sonolastic SL-1 for rigid pavements sections, should be considered for these purposes. A periodic inspection program should be conducted to identify the formation of cracks, eroded areas, and other indications of pavement distress, such as ruts, pot holes, areas of ponded water, etc. The need for possible patching and overlaying of the pavement system should be anticipated over the expected life of the pavement. 46

54 9.0 RECOMMENDATIONS FOR ANCILLARY STRUCTURES General site design recommendations for ancillary structures associated with the proposed development, such as the swimming pool, are offered in this section of the report. Recommendations concerning other potential ancillary structures, such as retaining walls, are not offered in this report since we do not believe that the final grading plans will include the need for retaining walls. In addition, if such retaining walls are required, we believe that they will be block retaining walls that will be designed by a block supplier/manufacturer and will not require any specific geotechnical recommendations. 9.1 SWIMMING POOL General We understand that a subsurface pool with surrounding concrete deck flatwork will be included in the proposed development. We anticipate that the pool will be constructed to depths ranging form 4 to 6 feet below the planned finished floor elevation of the project building. Stone edge treatment is usually placed around the perimeter of the pool. We anticipate that the concrete flatwork decking that is typically added to the areas surrounding the pool will be placed on a subgrade that is modified by the stripping of the existing topsoils and the stabilizing of the underlying subgrade soils with hydrated lime to a depth of approximately 6 inches as recommended for the proposed paved areas Subsurface Conditions We anticipate that the proposed pool will be located at the northeastern end of the proposed building location in the area of the existing 5-foot slope from the high level of the site to the low level. The nearest borings to the proposed pool location are believed to be borings B-4 for the proposed utility pole and boring B-5 in the proposed paved areas. The soils at the boring B-5 location mostly consist of clays of high plasticity. Laboratory test results indicated a PI value of 42 for the clays in one of the strata present at the boring B-5 location. The high plasticity clays are capable of significant magnitudes of shrink-swell movement with changing moisture contents. Moisture fluctuations can be induced by natural causes such as previously described in this report and also by development of the site as changed grading and drainage flow conditions, landscape waterings, and associated operational activities such as broken utility water or storm drain lines, or leakage from swimming pools. In addition, some long-term increases in the moisture content of subgrade soils can be expected due to the sealing off of the subgrade by the concrete deck slabs around the pool that prevent the natural loss of soil moisture by evaporation. Any appreciable volume changes (i.e., shrink-swell movements) of the soils along the sides or beneath the proposed swimming pool structure and the surrounding decking can cause distress to the pool 47

55 structure and surrounding flatwork. The distress to the pool and surrounding flatwork is typically manifested in the form of cracks and vertical displacements of the pool structure and decking Foundation Recommendations It is extremely difficult to prevent cracking of swimming pool structures and surrounding flatwork decking when pools are constructed within subsurface stratigraphies that contain potentially volumetrically active soils, such as at the present site. However, design of the pool and decking should consider one of the following design schemes to minimize possible distress to the pool structure: The most affirmative design scheme that would minimize the risk of distress to the pool structure due to shrinking or swelling of the foundation soils would be to construct the pool as a structural unit. CSC recommends the use of a structural unit for the pool if it is desired to minimize potential problems with the pool associated with shrinking or swelling of the foundation soils. Such a structural unit would have reinforced concrete (not gunite) walls and a reinforced concrete base. The pool structure would be supported on drilled piers with carton forms beneath the base of the pool structure to create a void space between the pool base and the underlying foundation soils, thus freeing the pool structure from contact with the potentially expansive soils. This type of construction was used with the recently constructed natatorium pool at the Texas A&M University College Station campus, but is relatively expensive to construct. We anticipate that other less affirmative of support the pool will also be considered due to construction budget limitations. The other forms of support would not involve construction of the pool as a reinforced concrete structure and would generally involve support of the pool directly on the foundation soils. The owner should be aware that the use of such ground supported pools constructed on expansive soils will involve an inherent risk of foundation movement and resulting distress to the pool structure. The ground supported pools would typically be constructed by first excavating the foundation soils beneath the pool to the planned founding depths. Reinforcing steel would then be placed along the sides and bottom of the excavation and gunite would be sprayed around the reinforcing steel to create the walls and the base of the pool. Some design procedures can be considered to minimize the distress that could occur with such construction as subsequently outlined. Performance of the ground supported pool would be improved if the existing high plasticity clays are first excavated below the base of the pool and the excavated soils replaced with volumetrically stable select fill soils. If select fill soils are utilized, they should contain an appropriate percentage of clays to discourage the ponding of water in the fill under the pool. Potential movements would depend upon the depth of excavation and replaced as outlined in Table 1 of this report. A subsurface drain system should be installed beneath the pool as part of the design scheme so that any water that leaks from the pool can be removed from the structure area and thereby reduce the possibility of ponding of the water in the select fill pad. Water that collects in the select fill pad can subsequently migrate into the underlying foundation soils present below the fill pad. The ponded water that subsequently seeps into the 48

56 pool foundation soils over time will produce expansion (swelling) of the underlying foundation soils and subsequent distress to the pool. Another potential method of design would involve pre-swelling of the potentially expansive soils in the area of the pool by moisture conditioning of the soils or by reducing the swell potential of the existing soils by treating them with hydrated lime. The foundation soils should be pre-swelled immediately prior to placement of the pool and the concrete deck slabs and the elevated moisture content maintained through the time of construction. The depth of moisture conditioning will depend upon the magnitudes of potential movement that can be tolerated by the pool structure. The constructed pool structure and surrounding deck slabs should serve as horizontal moisture barriers to seal-in the wet condition of the foundation soils. The decking surrounding the pool should be constructed as a structural slab that does not rely upon support from the potentially unstable subgrade soils. However, if some movement of the flatwork or decking can be accepted, then the flatwork may be placed on a pad of select fill soils to minimize potential foundation movements. The design of any subgrade supported decking around the pool structure should include the incorporation of numerous control joints in the concrete decking at spacings in the order of 6 to 8 feet on-center (or closer). The frequent jointing of the decking will help to reduce the cracking that occurs between the joints of the decking flatwork and will also facilitate sealing of the movements that do occur at the joints. Also, surface area drains should be located in the flatwork decking area surrounding the surface of the pool. The area drains should be sufficiently numerous to remove all surface water in an expeditious manner and to minimize the time that water ponds within the decking area. Following construction of the pool, a regular maintenance scheme should be implemented to quickly seal any cracks that do occur in the pool or decking structure. The sealant should be of a high quality elastomeric type that is suitable for applications that involve exposure to moisture and weather elements and for submerged conditions as applicable. Prompt application of the sealant to any cracks will minimize the migration of water through the cracks and the possible attendant increase in foundation movement and distress. 49

57 10.0 CONSTRUCTION CONSIDERATIONS General site development and construction recommendations for the proposed project are offered in the following subsections for consideration. These items should be considered minimum standards and are intended to be used in conjunction with project specifications SITE PREPARATION (CLEARING, STRIPPING AND DEMOLITION As previously mentioned, the site of the proposed development was previously occupied by a former building and some portions of the site are currently occupied by existing buildings of a quadplex with associated paving. Portions of the site are covered with native grasses and other portions of the site are occupied by existing paving and existing or former building slabs. We strongly recommend that all vegetation, organic matter, and topsoils be stripped and removed from the existing vegetated areas of the site. The removal of the vegetation should include all roots, including the major root systems associated with large trees which may either exist on the site at the present time or which may have previously be present on the site. The removal of the major root systems of the large trees should also include any desiccated soils present within the root bulbs of the trees. If the existing vegetation and desiccated soils are not removed prior to construction of the new buildings, it is possible that the organic materials and associated desiccated soils will interfere with the proposed construction and could potentially adversely impact the future performance of the proposed structures. Special attention should be directed to the removal of any existing organic materials or muck that may be present within former drainage swales, ponds, or other depressions on the site. In any event, all excavated organic materials and topsoils, including any potentially difficult to compact surficial clayey sands as subsequently discussed, should either be removed from the site or alternately, stockpiled and used as fill materials in proposed landscaped areas that will not have to support structural elements. The currently existing buildings and flatwork or paved areas as well as any remnants of previously existing structures, flatwork and paving should be demolished and the debris removed from the site. The demolition should include removal of all existing foundation elements. In addition, any underground tanks, pits and associated piping should be excavated, removed from the site and properly disposed. Furthermore, all abandoned utility lines and the backfill soils associated with those utility lines should be excavated from removed from the site. 50

58 10.2 PREPARATION OF BUILDING PAD SUBGRADE AND OTHER FILL AREA SUBGRADES Building Pad Excavation Any excavations associated with the construction of the building pad should be planned to ensure that the completed building pad is of uniform thickness, even if the existing ground surface of the site slopes across the areas of the proposed buildings (see Plate 1). If the building pad is constructed to a variable thickness across the area of the planned structure, it is possible that the magnitude of potential differential movements due to shrinking or swelling of the foundation soils will also increase in variability across the building area. As previously indicated and as subsequently defined in Section 10.4 of this report, any fill added to the site to construct the building pad for the proposed structure should consist of select fill soils with a low potential for shrink-swell movement Proof Rolling All building pad subgrade surfaces and the surfaces of subgrades in areas planned for fill placement that are exposed after the stripping of the vegetation and demolition of existing site elements should be proof-rolled with a 20-ton pneumatic roller or equivalent vehicle. Any soft or weak areas identified during proof-rolling should be removed and replaced with compacted select fill that is installed in accordance with the recommendations presented in Section The reasons for proof-rolling of the subgrade is that some soils have been found to compact to minimum density requirements but to still exhibit pumping tendencies. Proof-rolling of the subgrade should identify the soils that have a tendency to pump so that they can be removed and replaced with more suitable foundation soils. The earthwork contractor should recognize that there may be some areas of silty or fine sandy soils in the surficial zone that will likely pump during compaction if they are in a moist to wet condition at the time of construction. These weak surficial soils should be stripped from the site and replaced with select fill soils as subsequently defined Subgrade Soils Compaction and Testing All exposed subgrade soils present across the base of any stripped or excavated areas should be compacted to between 95 and 100 percent of the maximum density determined by the Standard Proctor compaction test (ASTM D e1 Standard Test Methods for Laboratory Compaction Characteristics of Soil Using Standard Effort (12,400 ft-lbf/ft 3 (600 kn-m/m 3 )) at moisture contents in the range of the optimum moisture content (OMC) to 4 percent above the OMC, inclusive. Compaction characteristics of the subgrade soils should be verified by in-place density tests. The tests should be 51

59 performed at an average rate of one test for every 2,000 square feet of building pad subgrade area, one test for every 5,000 square feet of paved area, with a minimum of three tests being performed for the subgrade layer GENERAL STORM WATER DRAINAGE AND MOISTURE CONTROL CONSIDERATIONS An adequate storm water drainage management plan that considers drainage both in the immediate vicinity of the proposed structure and also over the entire site of the proposed development should be formulated for the project Building Pad Areas Drainage and Moisture Control Considerations It is critical to satisfactory foundation performance that an adequate storm water management system be designed and installed around the areas of the proposed structure to discourage the ponding of water. Poor foundation and superstructure performance have been experienced when storm water runoff has not been controlled around the building pad area. Site grading plans should include the elevation of the finished floor of the building a significant height above the surrounding ground surface elevations so that final grades around the structure can be established to promote storm water runoff away from and around the perimeter of the structure. We recommend that the ground surface around the proposed building be sloped downward at grades of least 5 percent for a horizontal distance of at least 10 feet from the face of the structure to assure positive drainage away from the structure. Furthermore, the areas immediately surrounding the building should be covered or sealed on the surface with a relatively impermeable horizontal barrier as illustrated on Plate 1. The horizontal moisture barrier could consist of pavement, sidewalks, or other flatwork features. The flatwork should be frequently jointed and doweled across the joints so as to permit some movement without excessive cracking or vertical displacement across the joints that could cause interruption in planned storm water drainage flow patterns. There may be some landscaped areas around the exterior portion of the building that are not covered with flatwork. In areas with no flatwork we recommend that a surface cap of moderately plastic clays with a minimum thickness of 12 inches be installed over the top of the exterior portions of the building pad. The low permeability cap will help to minimize moisture infiltration into the building pad excavation. The moderately plastic clays should qualify as a CL type soil under the current USCS and as a CM type soil under the originally proposed USCS and should also have an LL value of between 30 and 49, inclusive, and a PI value of between 20 and 35, inclusive. 52

60 We also recommend that trees or other plantings requiring irrigation waterings not be placed in any landscaped areas immediately surrounding the proposed building. These plantings can serve as additional sources of moisture loss (tree root systems) or gain (landscape waterings) in the foundation soils. Any existing trees or any proposed trees that are to be planted in the general vicinity of the building should be located at a minimum horizontal distance away from the building equal to the height of the mature tree. This spacing requirement may require the removal of some existing trees or the root systems and soil bulbs of previously existing trees in the areas of the proposed building. As previously indicated, it is important that the removal of either any existing trees or any tree stumps or root systems of formerly existing trees include all desiccated clays associated with the root bulbs of the trees. Furthermore, we recommend that the storm water collected from the gutters and downspouts of the roof of the proposed building be routed through tight-lined piping attached to the end of the downspouts. The tight-lined piping should preferably discharge directly into proposed storm sewer pipes, drainage ditches, or alternately, to paved drive areas or to established drainage channels some distance away from and hydraulically down-gradient from the location of the proposed structure. In no event should roof drains be discharged immediately adjacent to the structure area or up-gradient of the structure area. Control of moisture in the building pad area is very important. If moisture is introduced into the building pad excavation, it can pond and remain within the building pad, especially if the pad was constructed using an excavation and replacement scheme involving the placement of more permeable select fill soils beneath the proposed building. Any ponded water within the building pad area can gradually migrate downward into the foundation soils below the base of the building pad and below the assumed zone of normal seasonal moisture change. The deeper moisture penetration can produce swelling of the foundation soils to a greater depth than originally anticipated. Therefore, unless a well conceived and effective drainage system can be constructed for the building pad area and the site, a subgradesupported slab should not be considered Site Drainage Considerations In addition to the drainage plan for the immediate area of the proposed building, a comprehensive drainage plan should also be devised for the entire site. The storm water management plan for the site should be formulated to assure that storm water is not routed toward and through the area of the planned building. It is particularly important that any existing drainage patterns at the site that promote storm water drainage toward the planned building location be modified as part of the site development plans. If necessary, consideration should be given to the use of perimeter interceptor ditches and landscaping berms to intercept surface water runoff before it migrates to the structure area. The intercepted storm 53

61 water should be routed around the perimeter of the area of the proposed building and discharged to the lower elevations of the site that are down-gradient of the building location BUILDING AREA ( SELECT ) FILL AND GENERAL PAVEMENT AREA FILL MATERIAL SELECTION AND PLACEMENT PROCEDURES We anticipate that fill materials may be placed in two distinct areas of the site as part of planned site development operations. One of these fill placement areas will be in the proposed building pad and is hereinafter referred to as select fill soils. The other area of possible fill placement is in the planned areas of pavement. The fill material that is placed in the planned paved areas is referred to as general pavement area fill or as general site fill (and NOT as select fill). Select fill placed in the building area or used to construct the building pad is also sometimes referred to as structural fill. Select or structural fill may be used in the building pad area for the purpose of replacing weak soils identified during proof-rolling operations, for replacing existing moderate to high plasticity clays that are excavated from the building area to reduce magnitudes of potential shrink-swell movements, and for general elevation or raising of the grade at the building pad area. The select or structural fill materials should meet the following criteria with respect to material properties: Select or structural fill material should consist of a low-plasticity material that classifies as either a clayey sand (SC type soil under the USCS) or a very sandy clay (CL type soil under the current USCS) with a PI between 10 and 18, inclusive, and a maximum LL of 38. The minimum plasticity is established so that purely granular soils are not used as select fill. The small percentage of clays in the select fill required to achieve the minimum PI of 10 should help to discourage moisture from storm water infiltrating into the soils of the building pads. Fill placed in the areas to be paved is referred to as general pavement area fill or general site fill and should meet the following criteria with respect to material properties: Fill placed outside of the building pad in areas planned to be paved may consist of low to moderate plasticity material that has PI values of between 19 and 30, inclusive, along with a maximum LL value of 49. The fill materials should generally classify as SC or CL type soils under the USCS or as SC, CL or CM type soils under the originally proposed USCS. Both types of fill materials should meet the following material requirements and should be placed according to the following procedures: Soils containing an excessive amount of silt (i.e., greater than approximately 20 to 25 percent) without a corresponding percentage of clays to balance the silts, should not be used for either select fill or for general pavement area fill. Soils that have the following material classifications under the USCS (ASTM D 2487) should not be used as select fill soils: CL-ML; ML; OL; SM; MH; CH, OH, and PT or a combination of these groups. The same soils should not be used as general site pavement area fill. 54

62 Compaction of the fill soils should be at moisture contents in the range of the OMC to a maximum of 4 percent above the OMC, inclusive, and should be in lifts that not exceed 8 inches in pre-compacted thickness and 6 inches in compacted thickness. The fill should be compacted to a density of at least 95 percent of the maximum dry density as determined by the previously specified Standard Proctor compaction test, ASTM D 698. Compaction characteristics of the fill should be verified by in-place density tests. The tests should be performed on each 6-inch-thick lift of fill at an average rate of one test for every 2,000 square feet of plan area for the building pad and one test for every 5,000 square feet of plan area for the paved portions of the project. A minimum of three (3) tests should be performed for each distinct lift of fill. Moisture migration through a concrete slab placed on top of the building pad fill soils can be discouraged by the use of a water-reducing admixture placed in the slab concrete and/or by the use of a polyethylene film placed beneath the slab DRILLED PIER EXCAVATIONS In general, the installation of deep foundation elements should be pursued in accordance with procedures outlined in The Deep Foundations Institute s Drilled Shaft Inspector s Manual, Second Edition, In addition, the following criteria should be followed during design and construction of the drilled piers or drilled footings, if used for this project: The drilled pier excavations should be checked to ensure that the shaft and bell size and founding depths specified on the plans have been achieved. Verification of the construction process and the dimensional characteristics of the piers or footings should be performed as part of the project quality assurance (QA) program. The drilled pier excavations should be inspected to ensure that all loose material greater than 3 inches dimension and all standing water over 2 inches depth have been removed prior to placement of the concrete. Precautions should be taken during placement of the reinforcement and concrete to prevent any loose excavated soil from entering into the excavation. Prompt placement of concrete into the pier excavation, as soon as the drilling is completed and the excavation cleaned and inspected, is strongly recommended. Under no circumstances should a pier be drilled that cannot be filled with concrete before the end of the workday. There is a possibility that ground water will enter the open pier excavations at the project site and will cause excessive sloughing of the pier excavation sidewalls. Therefore, the contractor should be prepared to use casing in order to ensure the integrity of the excavation and to permit pouring of pier concrete in a dry condition. The reinforcing steel cage placed in the pier shaft excavation should extend to no closer than 3 inches of the base of the shaft. An adequate number of reinforcement centralizers should be placed on each cage to ensure the referenced minimum cover of 3 inches. The cage should be designed from the standpoint of meeting three requirements: (1) structural requirements for wall or column loads imposed by the 55

63 supporting structure; (2) structural requirements for resistance of potential tensile forces attributable to swelling of foundation soils along the upper portion of the pier; and (3) stability requirements during placement of the concrete SHALLOW GRADE BEAM EXCAVATIONS The following criteria should be followed during design and construction of the grade beams or continuous footings: The grade beam or footing excavations should be checked for size and inspected to ensure that all loose material has been removed prior to placement of the reinforcing steel and concrete. As previously mentioned, it is possible that select fill soils will be used to construct thick building pad for the proposed building. These select fill soils will likely contain a significant percentage of sands and may be somewhat difficult to excavate as part of the construction of the grade beams or footings if the upper soils are wet due to antecedent precipitation at the time of construction. Low cohesive and granular materials that comprise the sidewalls of vertical cut excavations have a tendency to slough or slide into excavations until more stable side slopes are formed at shallower angles than vertical. Any such fall-in should be removed from the excavations. The contractor should take whatever actions are necessary, including the use of wooden forms, to maintain the stability of the grade beam or footing excavations so as to be able to complete placement of reinforcing steel within the planned grade beam or footing cross-section. In addition, if the excavations occur during or immediately after periods of heavy rainfall, there may be problems with temporarily high or perched ground water. The possible need for storm water interceptor ditches, sumps, and sump pumps should be anticipated. We strongly recommend the prompt placement of concrete into the grade beam or footing excavations immediately following completion of digging, cleaning, placement of reinforcing steel, and inspection of the excavation. Precautions should be taken during placement of the reinforcement and concrete to prevent any loose excavated soil from entering into the excavation. Any clods of earth that slump into the grade beam or footing excavations during concrete placement should be promptly removed. Under no circumstances should a grade beam or footing be excavated that cannot be filled with concrete before the occurrence of a significant rainfall event. Such a rainfall event could flood the grade beam or footing excavations and result either in the creation of a weak saturated soil layer or in the collection of eroded soils across the bottoms of the excavations. Grade beams or footings supported on such layers of weak, saturated soils or loose, eroded soils could experience greater magnitudes of settlement than were previously presented in this report. The reinforcing steel placed in the grade beams or footings should extend to no closer than 3 inches from the base or sides of the excavations in order to achieve the minimum cover requirements specified by the American Concrete Institute (ACI). Verification of the construction process, the dimensional characteristics of the grade beams or footings, the size and pattern of all reinforcing steel bars as specified on the construction plans should be performed as part of the project quality assurance (QA) program. 56

64 10.7 FOUNDATION CONCRETE The following specifications should be employed during construction of the recommended foundation: The concrete used for the construction of all foundation elements should consist of a mix that has been shown to comply with the requirements of ACI 214 and ACI 301, Section Submitted mix designs should indicate that the aggregates have been tested in accordance with ASTM C 33 within a time period that does not exceed one year. If fly ash is used in the concrete, the replacement percentage should not exceed 20 percent of the total cementitious material. The concrete should have a minimum 28-day design compressive strength of 3,500 psi as determined in accordance with ASTM C 39, unless otherwise specified on the architectural, structural, or civil drawings. A test set, consisting of four cylinders, should be cast during each placement at a rate of one set for every 75 yd 3 of concrete placed with at least one set cast during each placement day. One cylinder should be tested for compression strength at 7 days following placement and two cylinders should be tested at 28 days following placement. The fourth cylinder should be held in reserve pending the evaluation of the compression test results for the other three cylinders and may be either tested or discarded based upon the evaluation. Water may be added to the mix at the site by an experienced materials engineer in order to develop design workability, but only to the extent that the water/cement ratio does not exceed 0.55 lb/lb. An appropriate percentage of air entrainment admixture should be added to the concrete. 57

65 11.0 BASIS OF RECOMMENDATIONS The recommendations contained in this report are based, in part, on the project information provided to CSC. If statements or assumptions made in this report concerning the location and design of project elements contain incorrect information, or if additional information concerning the project becomes available, the owner should convey the correct or additional information to CSC. The field exploration, which provided information concerning subsurface conditions, was considered to be in sufficient detail and scope to form a reasonable basis for the conceptual planning and design of the foundation systems of the proposed building and paved areas. Recommendations contained in this report were developed based upon a generalization of the subsurface conditions encountered at the boring locations across the site and the assumption that the generalized conditions are continuous throughout the building areas under consideration. However, regardless of the thoroughness of a subsurface exploration, there is always a possibility that subsurface conditions encountered over a given area will be different from those at specific, isolated boring locations. Consequently, we recommend that experienced geotechnical personnel be employed to observe construction operations and to document that conditions encountered during construction conform to the assumed generalizations that formed the basis for the recommendations presented in this report. In addition, the construction observers should document construction activities and field testing practices employed during the earthwork and foundation construction phases of the project. Also, the construction project manager should review the results of all field and laboratory construction materials tests for conformance with the recommendations presented in this geotechnical report and in the project construction documents. Questionable procedures and/or practices and non-conforming test results should be reported in a timely manner to the owner and the designers, along with current recommendations to solve any issues raised by the questionable procedures, practices, and/or test results. The Geotechnical Engineer warrants that the findings, recommendations, specifications, or professional advice contained herein have been made after preparation in accordance with generally accepted professional engineering practice in the field of geotechnical engineering in this geographic area. No other warranty is implied or expressed. The information presented in this report was presented for the specific site and the specific structure described in the report. The information should not be employed for the design for other structures or for other projects in the general area of the subject project without the express written consent of CSC. 58

66 CSC ENGINEERING & ENVIRONMENTAL CONSULTANTS, INC. APPENDIX A Figures Figure 1 Project Vicinity Map Figure 2 Site Plan and Plan of Borings Figure 3 Subsurface Profile A-A Boring Log B-1 through B-8 Key Sheets to Terms and Symbols Used on the Boring Logs

67 PROJECT SITE R:\ACAD GRAPHICS\GEOTECH\HOME 2 SUITES\FIGURE 1 PROJECT VICINITY MAP.dwg, 1:1 Source Map: Texas Department of Transportation Urban Files - Brazos County Map Modifications: Property Location (CSC 2012) C S C VASU DEMLA, LLC FEET PROJECT VICINITY MAP PROJECT NO.: LOCATION: COLLEGE STATION, TEXAS APPR: MFC REV. DATE: -- DRAWN BY: AEA SCALE: AS SHOWN DATE: 02/24/12 FIGURE NO.: 1

68 A B-6 (6') B-5 (6') B-1 (50') B-1 (50') HAMPTON INN B-7 (15') PROPOSED BUILDING B-2 (30') A A' B-4 (40') B-2 (30') B-3 (30') APPLEBEE'S FEET B-8 (6') B-4 (40') C S C PLAN OF BORINGS HOME 2 SUITES DEVELOPMENT A' VASU DEMLA, LLC PROJECT: LOCATION: COLLEGE STATION, TEXAS APPR: MFC REV. DATE: DRAWN BY: AEA SCALE: AS SHOWN DATE: 03/12/12 FIGURE NO.: 2