GEOTECHNICAL ENGINEERING RECOMMENDATIONS MONTEZUMA COUNTY COMBINED COURT SYSTEMS BUILDING. Cortez, Colorado

Transcription

1 GEOTECHNICAL ENGINEERING RECOMMENDATIONS MONTEZUMA COUNTY COMBINED COURT SYSTEMS BUILDING Cortez, Colorado Prepared For: Ms. Melissa Brunner, Montezuma County Project Number: 54077GE

2 1.0 REPORT INTRODUCTION Scope of Project GEOTECHNICAL ENGINIEERING STUDY Geotechnical Engineering Study Scope of Service FIELD STUDY Project location Site Description and Geomorphology Subsurface Soil and Water Conditions Anticipated Excavation Characteristics of the Formational Materials Excavation Cut to Embankment Fill Shrink/Swell Factors Site Seismic Classification LABORATORY STUDY FOUNDATION RECOMMENDATIONS Spread Footings Supported by the Competent Formational Sandstone Material Spread Footings Supported by the Site Clay Soil Materials General Shallow Foundation Considerations RETAINING STRUCTURES SUBSURFACE DRAIN SYSTEM CONCRETE FLATWORK Interior Concrete Slab-on-Grade Floors Exterior Concrete Flatwork Considerations General Concrete Flatwork Comments PAVEMENT SECTION THICKNESS DESIGN RECOMMENDATIONS Asphalt Pavement Recommendations Rigid Concrete Pavement Recommendations General Parking Area Considerations CONSTRUCTION CONSIDERATIONS Fill Placement Recommendations Natural Soil Fill Granular Compacted Structural Fill Excavation Considerations Excavation Cut Slopes Utility Considerations Exterior Grading and Drainage Comments Landscaping Considerations Soil Sulfate Content, Corrosion Issues Radon Issues CONSTRUCTION MONITORING AND TESTING CONCLUSIONS AND CONSIDERATIONS

3 1.0 REPORT INTRODUCTION This report presents our geotechnical engineering recommendations for the Montezuma County Combined Court System Project. This report was requested by Melissa Brunner, Montezuma County Administrator. The field study was performed on January 7 through January 20, The laboratory study was completed on January 25, We provided verbal recommendations and consultation to members of the design team during the preparation of this report. Geotechnical engineering is a discipline which provides insight into natural conditions and site characteristics such as; subsurface soil and water conditions, soil strength, swell (expansion) potential, consolidation (settlement) potential, and often slope stability considerations. Typically the information provided by the geotechnical engineer is utilized by many people including the project owner, architect or designer, structural engineer, civil engineer, the project builder and others. The information is used to help develop a design and subsequently implement construction strategies that are appropriate for the subsurface soil and water conditions. It is important that the geotechnical engineer be consulted throughout the design and construction process to verify the implementation of the geotechnical engineering recommendations provided in this report. Generally the recommendations and technical aspects of this report are intended for design and construction personnel who are familiar construction concepts and techniques, and understand the terminology presented below. We should be contacted if any questions or comments arise as a result of the information presented below. The following outline provides a synopsis of the various portions of this report; Sections 1.0 and 2.0 provide an introduction and an establishment of our scope of service. Sections 3.0 and 4.0 of this report present our geotechnical engineering field and laboratory studies Sections 5.0 through 9.0 presents our geotechnical engineering design parameters and recommendations which are based on our engineering analysis of the data obtained. Section 10.0 provides a brief discussion of construction sequencing and strategies which may influence the geotechnical engineering characteristics of the site. The discussion and construction recommendations presented in Section 10.0 are intended to help develop site soil conditions that are consistent with the geotechnical engineering recommendations presented previously in the report. Ancillary information such as some background information regarding soil corrosion and radon considerations is presented as general reference. The construction considerations section is not intended to address all of the construction planning and needs for the project site, but is intended to provide an overview to aid the owner, design team, and contractor in understanding some construction concepts that may influence some of the geotechnical engineering aspects of the site and proposed 2

4 development. The data used to generate our recommendations are presented throughout this report and in the attached figures. 1.1 Scope of Project We understand that the proposed project will consist of constructing a pre-engineered metalframed building that is supported by a steel reinforced concrete foundation system. A partial basement with a mechanical room and sally port will be constructed under the northern portion of the building. A combination of concrete slab-on-grade and structurally supported floors (at minimum over basement areas) will be used for the interior building floor system. The development will include asphalt pavement driveway and parking areas as well as exterior concrete flatwork. 2.0 GEOTECHNICAL ENGINIEERING STUDY This section of the report presents our geotechnical engineer scope of services to date for the project. Our services include a geotechnical engineering study of the subsurface soil and water conditions of this site for development of a foundation design and pavement section thickness study for the proposed use. 2.1 Geotechnical Engineering Study Scope of Service The scope of our study which was delineated in our proposal for services, and the order of presentation of the information within this report, is outlined below. Field Study We advanced eighteen (18) continuous flight auger test borings and two (2) NW wireline core borings at the project within the areas we understand are planned for construction of the proposed structure and parking/landscape areas. Select driven sleeve and bulk soil samples were obtained from the test borings and returned to our laboratory for testing. 3

5 Laboratory Study The laboratory testing and analysis of the samples obtained included; Moisture content and dry density, Direct shear strength tests, to help establish a basis for development of soil bearing capacity and lateral earth pressure values, Unconfined compressive strength tests on select sections of rock core obtained from our wireline core borings, Swell/consolidation tests to help assess the expansion and consolidation potential of the support soils on this site to help estimate potential uplift associated with expansive soils and to help estimate settlement of the foundation system, Plastic and liquid limit tests to determine the Plasticity Index of the soil, Sieve analysis tests, Moisture content/dry density relationship (Proctor) tests, and, California Bearing Ratio (CBR) tests. Geotechnical Engineering Recommendations This report addresses the geotechnical engineering aspects of the site and provides recommendations including; Geotechnical Engineering Section(s) Subsurface soil and water conditions that may influence the project design and construction considerations, Geotechnical engineering design parameters including; Viable foundation system concepts including soil bearing capacity values, settlement considerations for the foundation system concepts that are viable for this project, Lateral Earth Pressure values for design of retaining structures, and, Flexible asphalt concrete pavement thickness design considerations Soil support considerations for interior and exterior concrete flatwork Construction Consideration Section Fill placement considerations including cursory comments regarding site preparation and grubbing operations, 4

6 Considerations for excavation cut slopes, Natural soil preparation considerations for use as backfill on the site, Compaction recommendations for various types of backfill proposed at the site, Utility trench comments, and, Cursory exterior grading considerations This report provides design parameters, but does not provide foundation design or design of structure components. The project architect, designer, structural engineer or builder may be contacted to provide a design based on the information presented in this report. Our subsurface exploration, laboratory study and engineering analysis do not address environmental or geologic hazard issues other than expansive soil conditions. 3.0 FIELD STUDY 3.1 Project location The project site is located west of the intersection of North Park Street and East Driscoll Street, just south of the existing Montezuma County Detention Center. Figure 3.1 shown below obtained from Google Earth imagery indicates the location of the project site. 5

7 Figure 3.1: Project Location Project Location N 3.2 Site Description and Geomorphology The project site is located on a previously undeveloped approximate 6.8 acre lot. The project site is relatively barren with vegetation consisting of sparse sage brush and grass cover. The ground surface on the project site generally slopes down to the north with slope inclinations in the range of about fifteen to one (15:1, horizontal to vertical) or flatter. A relatively shallow drainage feature with a gradient down to the north towards Park Street exists in the north central portion of the lot. The geomorphology in the vicinity of the project consists of a relatively shallow wind-blown loess deposit consisting of fine sands and clay and silt soil materials overlying the Dakota Sandstone Formation. The clay soil materials encountered in the vicinity of the project may exhibit a moderate to high swell potential and moderate consolidation potential under typical foundation loads. The Dakota Sandstone Formation consists of interbedded layers of sandstone, claystone, and shale materials. Lignite (coal like material) is sometimes encountered within the formational material. The claystone and shale materials encountered within the formational material may exhibit a moderate to high swell potential. 6

8 Subsurface water is often encountered in the vicinity of the project. We suspect that the source for this subsurface water is the relatively heavily irrigated park system and related canal systems located to the southeast of the subject project site. Water may be encountered over the formational sandstone material or within fractures within the formational materials. 3.3 Subsurface Soil and Water Conditions We advanced eighteen (18) continuous flight auger test borings and two (2) NW wireline core borings in the vicinity of the proposed structure and proposed parking/landscape areas. The surveyed location of our test borings relatively to the approximate location of the structure are shown on Figure 3.3 below. The surveying and development of the figure below was provided to us by Maness and Associates. The logs of the soils encountered in our test borings are presented in Appendix A. Figure 3.3: Test Boring Locations N 7

9 The test boring locations were survey located however the location of the structure footprint relatively to our test borings has been approximated. We understand that the building location relative to our test boring locations should be accurate to within a few feet. The following provides a general description of the subsurface conditions that we encountered in our test borings. The logs of the test borings presented in Appendix A should be consulted for more precise information. Generally, we encountered sandy clay soil material from the ground surface to depths ranging from about one and one-half (1½) to as deep as about eight (8) feet below the ground surface where we encountered the Dakota Sandstone Formation. The upper approximate one (1) foot of sandy clay soil materials were generally very moist and soft, becoming stiffer and drier with depth. The clay soil materials encountered and tested exhibit a low to moderate swell potential, and moderate to high consolidation potential. The formational material was encountered at depths ranging from about one and one-half (1½) to about eight (8) feet below the ground surface elevation. The upper portion of the formational material was very hard. All of our auger test borings, with exception to Test Borings Four through Seven, were advanced to refusal within about one-half (1/2) to one (1) foot of penetration into the formational material. We were able to advance auger Test Borings Four through Seven through the upper very hard sandstone material into more friable sandstone material and claystone materials. The claystone materials were encountered at depths ranging from about ten (10) to fifteen (15) feet below the ground surface. Test Borings Four through Seven were advanced to refusal on a deeper very hard sandstone layer encountered at depths ranging from about eighteen (18) to as deep as about thirty-eight (38) feet below the ground surface elevation. We advanced two (2) NW wireline core borings in the vicinity of the project (eastern area of the proposed structure location) where we encountered shallow auger drilling refusal. We have referred to these core borings as TB-2A and TB-10A. In TB-2A we encountered sandy clay soil material from the ground surface to a depth of about two (2) feet below the ground surface elevation where we encountered very hard sandstone formational material. The formational material encountered consisted of very hard and moderately fractured sandstone to a depth of about seven (7) feet below the ground surface. At depths ranging from about seven (7) to twelve (12) feet below the ground surface we encountered highly fractured and more friable sandstone material. We encountered highly fractured clayey sandstone to sandy claystone at depths ranging from about twelve (12) feet below the ground surface to a depth of about twenty (20) feet below the ground surface where primarily sandstone material was encountered. TB-2A was advanced to a depth of about twenty-two (22) feet below the ground surface elevation. 8

10 In TB-10A we encountered sandy clay soil materials from the ground surface to a depth of approximately five (5) feet below the ground surface where we encountered hard claystone material to a depth of about seven (7) feet below the ground surface. Very hard and moderately fractured sandstone material was encountered at a depth of about seven (7) feet below the ground surface elevation to the bottom of the core boring advanced to twelve (12) feet below the ground surface elevation. Subsurface free water was initially encountered at a depth of about twenty-five (25) feet below the ground surface elevation in Test Boring Four. Subsequent measurements of the free water elevation in Test Boring Four were at about twenty-one (21) feet below the ground surface. We measured subsurface free water at a depth of about sixteen (16) feet below the ground surface elevation in Test Boring/Core 2A. The free water was encountered in fractures within the formational materials. We anticipate that the source area for this free water is from the heavily irrigated park system and associated canals located a relatively short distance to the southeast of the project site. Based on the subsurface information obtained we anticipate that the proposed structure will be located above the static water elevation for the area. However we anticipate that a periodic or seasonal water surface may develop over the formational sandstone material or within fractures in the upper portions of the formational sandstone materials within the extent of the structure depth during periods of high precipitation or spring snow melt. This is due to the relatively shallow depth and impermeable nature of the formational sandstone material below and adjacent to the project site. Our recommendations for a subsurface drain system may be found in Section 7.0 of this report. The logs of the subsurface soil conditions encountered in our test borings are presented in Appendix A. The logs present our interpretation of the subsurface conditions encountered exposed in the test borings at the time of our field work. Subsurface soil and water conditions are often variable across relatively short distances. It is likely that variable subsurface soil and water conditions will be encountered during construction. Laboratory soil classifications of samples obtained may differ from field classifications. 3.4 Anticipated Excavation Characteristics of the Formational Materials Based on our understanding of the proposed structure finished floor elevations we anticipate that at minimum the entire basement area foundation system will be located within the formational sandstone materials. The main level foundation system may be slightly below the formational sandstone materials in some areas of the structure footprint. As discussed above, the upper portions of the formational sandstone material were very hard. We experienced auger refusal with our four (4) inch diameter solid stem auger utilizing our approximate 12,000 pound CME-45 drilling equipment in many areas of the structure footprint and proposed exterior landscape areas. Due to the auger refusal experienced during our initial 9

11 field study we advanced additional NW wireline core borings in select locations of the structure area (TB-2A and TB-10A). The upper approximate five (5) to six (6) feet of the formational materials encountered exhibited Rock Quality Designation (RQD) values in the range of about 60% to 85%, meaning relatively competent sandstone with moderate to low fracturing. We performed unconfined compressive strength testing of select sections of rock core obtained from the upper portions of the formational sandstone material. The compressive strength of the rock core tested ranged from about 4,500 pounds per square inch (psi) to over 10,000 psi. The formational materials encountered below the upper approximate five (5) to six (6) feet of the surface of the formation were considerably more fractured and friable with a compressive strength in the range of about 1,000 psi. Based on our understanding of the structure finished floor and basement floor elevations, the structure basement foundation system will be located within the very hard sandstone materials that exhibited moderate to low fracturing with compressive strengths ranging from about 4,500 psi to over 10,000 psi. We anticipate that blasting will be necessary to efficiently remove the very hard sandstone formational materials in some areas of the project. Blasting must be performed very carefully by an experienced blaster to ensure that the foundation bearing materials are not compromised for support of the structure. Careful attention must be given to post blasting operations to insure that the foundation support materials have not been compromised or portions of the formational materials located behind the proposed basement retaining walls have not been destabilized. We are available to assist with these post blasting observations. Where possible, we recommend that alternative excavation methods be used to more precisely excavate the foundation bearing support elevation with less potential for disturbance to the foundation support materials. 3.5 Excavation Cut to Embankment Fill Shrink/Swell Factors We understand that excavation cut and embankment fill construction will be used to establish the project site grade(s). This section of the report provides estimated shrink/swell factors for excavated material that will be placed and compacted as embankment fill. The factors provided are applicable for the sandy clay soil materials located above the formational sandstone materials. All embankment fill placed on the project site should be compacted to at least ninety (90) percent of the Modified Proctor (ASTM D1557). The factor provided below is based on an average value of the existing in-place density for the native sandy clay soil materials compacted to ninety (90) percent of the Modified Proctor (ASTM D1557). We obtained a number of driven Modified California Barrel liners within the native sandy clay soil materials; however the number of samples that could be obtained was limited due to the relatively shallow depth of the formational material underlying the project site. The dry density and moisture content of these liner samples are tabulated in Section 4.0 below. An average dry density of about 117 pounds per cubic foot was obtained for the liner samples obtained and tested 10

12 from the sandy clay soil materials that overlie the formational sandstone material. The results of the Modified Proctor test are presented in Section 4.0 below. We obtained a maximum dry density of about 124 pounds per cubic foot at an optimum moisture content of about 11.0 percent. Based on ninety (90) percent compaction, embankment fill material should be compacted to about 112 pounds per cubic foot. Therefore we anticipate that it will require between about 0.96 cubic yards of excavation cut within the site sandy clay soil materials to produce about 1.0 cubic yard of embankment fill material. Therefore the swell factor from excavation cut to embankment fill appears to be in the range of about This value is not applicable for the formational materials. We estimate a swell factor of about 1.2 from excavation cut to embankment fill for the competent formational sandstone materials. 3.6 Site Seismic Classification The seismic site class as defined by the 2009 International Building Code is based on some average values of select soil characteristics such as shear wave velocity, standard penetration test result values, undrained shear strength, and plasticity index. Based on our standard penetration field tests and laboratory test results we feel that the subsurface conditions for the project are consistent with the criteria for a Site Class C designation as outlined in the 2009 International Building Code, Table The table below presents seismic site coefficients for the project site based on a Site Class C designation in conjunction with the mapped short period acceleration and long period acceleration. The spectral response maps and subsequent seismic site coefficients were obtained from the 2009 International Building Code Specifications. Mapped Spectral Short Period Acceleration S s (Figure (1)) Mapped Spectral 1-second Acceleration S 1 (Figure (2)) Short Term Period Site Coefficient F a (Table (1)) Long Term Period Site Coefficient F v (Table (2)) 0.20g 0.06g

13 4.0 LABORATORY STUDY The laboratory study included tests to estimate the strength, swell and consolidation potential of the soils tested. We performed the following tests on select samples obtained from the test borings. Moisture content and dry density; the moisture content and in-situ dry density of some of the soil samples were assessed in general accordance with ASTM D2216. The results of the moisture content and dry density tests performed are tabulated below. Sample Identification Sample Wet Density Sample Moisture Sample Dry Density and Depth (pcf) Content (%) (PCF) TB-3: 1.5 feet TB-4: 13.5 feet TB-5: 2 feet TB-6: 4.5 feet TB-8: 3.5 feet TB-11: 1 foot Atterberg Limits and Sieve Analysis; the plastic limit, liquid limit and plasticity index of some of the soil samples was determined in general accordance with ASTM D4318. In conjunction with the Atterberg Limits tests, sieve analysis tests were performed in general accordance with ASTM D422 and D1140. The results of the sieve analysis and Atterberg Limits testing performed are provided in Appendix B, Figures 4.1 through 4.6. The sandy clay soil materials encountered and tested classify as USCS type CL or AASHTO type A-6 sandy lean clay material. The Plasticity Index of the clay soils tested range from about 9 to 16. One Dimensional Swell-Consolidation Tests; the one dimensional swell-consolidation potential of some of the soil samples obtained was determined. The soil sample tested is exposed to varying loads and the addition of water. The one-dimensional swell-consolidation response of the soil sample to the loads and/or water is represented graphically in Appendix B, Figures 4.7 through The basic information obtained from the swell-consolidation tests performed is tabulated below. We performed a swell pressure/ swell potential only for the test performed on TB-2A at a sample depth of seventeen (17) feet therefore the swell/consolidation graph was not produced for this sample. The results of the swell pressure/potential for this test are provided below. 12

14 Sample Designation TB-2A: 17 feet (claystone) TB-3: 1.5 feet (sandy clay) TB-4: 13.5 feet (claystone) TB-5: 2 feet (sandy clay) TB-6: 4.5 feet (sandy clay) TB-8: 3.5 feet (clayey sandstone) TB-11: 1 foot (sandy clay) Initial Moisture Content 11.1% Initial Dry Density (pcf) (remold) Swell Pressure (psf) 3.3% % % % % % Swell Potential (percent) -- (100 psf surcharge load) -- (100 psf surcharge load) 1.0% (100 psf surcharge load) -- (100 psf surcharge load) 0.3% (100 psf surcharge load) 0.2% (100 psf surcharge load) 0.9% (100 psf surcharge load) Based on our laboratory test data the site clay soil materials and claystone materials encountered within the formational materials exhibit a low to moderate swell potential. The sandy clay soil materials encountered and tested that overlie the formational materials exhibited a moderate to relatively high consolidation potential when exposed to typical spread footing foundation pressures. Unconfined Compressive Strength; the unconfined compressive strength of select sections of the NWL (NQ diameter) core were tested for strength in our concrete press. The results of the unconfined compressive strength tests are presented below. NQ Core Boring and Depth (feet below the ground surface) Unit Weight (pcf) Ultimate Compressive Strength (psi) TB-2A at 2.5 feet TB-2A at 10.0 feet ,650 1, feet ,520 Rock Quality Determination (RQD); The relative quality with regard to degree of fracturing of the core was determined. The results of the RQD tests may be found on the NWL core logs presented in Appendix A. The formational materials encountered in our core borings may be generally considered as being moderately to highly fractured. 13

15 Direct Shear Strength tests; direct shear strength tests were performed on select soil samples to estimate the soil strength characteristics in general accordance with ASTM D3080. Based on the test results, we used an angle of internal friction of thirty (30) degrees and cohesion of about 50 pounds per square foot for the sandy clay soil materials encountered in the upper soil strata. The results of the direct shear strength test are shown on Figure Moisture content-dry density relationship (Proctor) tests; We performed laboratory moisture content-dry density tests to assess the relationship between the soil moisture content and dry density. The Proctor tests were performed in general accordance with ASTM D1557. We obtained a maximum dry density of about pounds per cubic foot at an optimum moisture content of about 11.0% for the sandy clay soil materials encountered at the project site. The results of the laboratory Proctor tests are presented on Figures California Bearing Ratio (CBR) Tests; We assessed the pavement section support characteristics of select composite soil samples in general accordance with ASTM D1883. We obtained a CBR value of about six (6) for the sandy clay subgrade soil materials compacted to about ninety (90) percent of the maximum dry density as defined by the Modified Proctor test (ASTM D1557). The results of the CBR tests are presented on Figure FOUNDATION RECOMMENDATIONS Based on the subsurface conditions encountered and laboratory test data obtained, we feel that the proposed structure may be supported by a conventional spread footing foundation system. As discussed above, based on the data available to us at the time this report was prepared, the entire basement/sally port corridor areas will extend into the competent formational materials. The structure perimeter foundation system will be located on or within about two (2) feet of the formational sandstone material for a typical depth bottom of footing elevation around the southwest and majority of the southeast sides of the structure. However we anticipate that the formational materials will be located more than two (2) feet to possibly as much as about six (6) feet below a typical depth bottom of footing elevation for the northeastern area of the structure. Section 5.1 below provides bearing capacity values and construction considerations for extending the entire structure foundation system to bear on a layer of structural fill and/or lean concrete fill that extends to the competent formational sandstone material. This footing support strategy limits the potential for post construction differential settlement to occur in the foundation system. The competent formational sandstone materials will provide a relatively high bearing capacity value with minimal potential for post construction settlement or heave due to expansive soil conditions. We calculated that the potential differential settlement between 14

16 portions of the foundation system supported on the formational sandstone material versus portions of the foundation system supported on the site clay soil materials that overlie the formational material could be in the range of one (1) inch or greater. Therefore we do not recommend that the structure foundation system bear on the different material types. Section 5.2 provides bearing capacity values for supporting spread footings on the site sandy clay soil materials. These recommendations are applicable for ancillary structures (that are not structurally connected to the main structure) such as exterior retaining wall structures. We are available to provide alternative foundation recommendations such as drilled caissons at your request, however we do not feel that the use of a drilled caisson foundation system is necessary based on the subsurface conditions encountered and laboratory test data. The integrity and long-term performance of any foundation system is influenced by the quality of workmanship which is implemented during construction. It is imperative that all excavation and fill placement operations be conducted by qualified personnel using appropriate equipment and techniques to provide suitable support conditions for the foundation system. 5.1 Spread Footings Supported by the Competent Formational Sandstone Material The sketch provided below is intended to provide insight regarding the depth of the competent formational sandstone material below the various areas of the structure layout. This figure is based on the approximate location of our test borings relative to the proposed building footprint as provided to us by Maness and Associates, the existing topography of the ground surface around the structure area, and our understanding of the various finished floor elevations of the structure. The actual depth of the formational sandstone material below the chosen footing support elevation will likely vary somewhat from the approximate depths shown below. The figure below is based on the following assumptions; The finished floor elevation of the main structure floor system will be at an elevation of about feet. We have assumed a bottom of footing depth for the structure perimeter footings of about feet. This portion of the foundation system is outlined in the colors yellow and red in the sketch shown below. The finished floor elevation of the basement mechanical/electrical rooms and basement corridor sally port will be at an elevation of about feet. We have assumed a bottom of footing elevation for the structure basement/corridor walls of about feet. This portion of the foundation system is outlined in green in the sketch below. 15

17 N Foundation system located within competent formational sandstone materials Foundation system located near or about two (2) feet above competent formational sandstone Foundation system located about two (2) to as deep as about six (6) feet above competent formational sandstone The general foundation preparation strategy provided below should be followed for supporting the entire structure foundation system on the competent formational sandstone materials. 16

18 The footing excavation should extend to the competent formational sandstone material. Loose debris from the excavation (or blasting) operations must be removed to expose competent formational sandstone material. We recommend a minimum structural fill depth of eight (8) inches be placed to help achieve a uniform footing support elevation and to aid in the construction of concrete formwork. For areas of the structure where the chosen footing support elevation is located within about two and one-half (2½) feet of the competent formational material, an imported structural fill may be placed and compacted to establish the bottom of footing elevation. For areas where the competent formation sandstone material is located between about two and one-half (2½) feet or more below the chosen bottom of footing elevation we recommend that a lean concrete fill be used to backfill the bottom of the footing excavation to within about two (2) to two and one-half (2½) feet of the bottom of footing elevation. An imported structural fill material may then be placed and compacted to establish the bottom of footing elevation. The lean concrete fill material must be adequately cured prior to placement of the compacted structural fill material. The structural fill material should be compacted to at least ninety (90) percent of the maximum dry density as defined by ASTM D1557, Modified Proctor. In general we recommend that the structural fill material consist of Colorado Department of Transportation (CDOT) Class 6 material. Other types of structural fill material may suitable as well. We are available to assess other material types for use as structural fill material as the project progresses. The lean concrete fill material should consist of a minimum two (2) sack Portland cement mix. A maximum lift thickness of about three (3) feet should be placed and allowed to cure prior to placement of additional lifts of lean concrete fill. A higher strength lean concrete fill such as a three (3) to four (4) sack mix may be used if it is desired to speed up the strength gain curing process and/or if cold ambient air conditions are present that would hamper the curing of lighter mixes. The lean concrete fill material may be placed neat within the foundation trench excavation. The width of the lean concrete fill trench excavation should be equal to the width of the structural fill material. The figure provided below indicates the necessary width of structural fill material below the footing. Alternatively, if it is acceptable by the project structural engineer, the foundation system may be stepped to limit the depth of fill materials under the footings. 17

19 The compacted structural fill should be placed and compacted as discussed in the Construction Considerations, Fill Placement Recommendations section of this report, below. The zone of influence of the footing (at elevations close to the bottom of the footing) is often approximated as being between two (2) lines subtended at 45 degree angles from each bottom corner of the footing. The compacted structural fill should extend beyond the zone of influence of the footing as shown in the sketch below. Footing Zone of Influence Concept Footing 45 degrees 45 degrees Footing Zone of Influence No Scale A general and simple rule to apply to the geometry of the compacted structural fill blanket is that it should extend beyond each edge of the footing a distance which is equal to the fill thickness. Spread footings and isolated footings may be designed using an allowable gross bearing capacity of 4,500 pounds per square foot. The allowable gross bearing capacity may be increased by twenty (20) percent due to transient loads. A coefficient of friction of 0.45 (based on structural fill characteristics) may be used for lateral sliding calculations. All footings should have a minimum depth of embedment of at least one (1) foot. The embedment concept is shown below. 18

20 Minimum depth of embedment Footing Footing Embedment Concept No Scale We estimate that the footings designed and constructed as discussed above will have a total post construction settlement of less than one-half (1/2) inch. Differential settlement between various portions of the foundation system will be less than one-half (1/2) inch. All footings should be support at an elevation deeper than the maximum depth of frost penetration for the area. This recommendation includes exterior isolated footings and column supports. We understand that the code frost depth for the City of Cortez is thirty-two (32) inches. 5.2 Spread Footings Supported by the Site Clay Soil Materials This section of the report provides bearing capacity values for the site sandy clay soil materials that overlie the formational materials. These recommendations are applicable for ancillary structures such as exterior retaining wall footings that are not structurally attached to the main structure. The sandy clay soil materials encountered and tested exhibit swell pressures in the range of about 300 to up to 900 pounds per square foot with a magnitude of swell potential up to about one (1) percent when exposed to a 100 pound per square foot surcharge load. The site clay soil materials encountered may be considered as having a low to perhaps moderate swell potential. The samples tested exhibit a moderate to relatively high consolidation potential when exposed to typical spread footing foundation pressures. 19

21 Properly designed and constructed continuous spread footings with stem walls/retaining walls (beams) have the ability to distribute the forces associated with movement in the support soils. The rigidity of the system helps reduce differential movement and associated damage to the structure. Movement within the soils supporting isolated pad footings will result in direct movement of the supported component. Damage to the structure due to this type of movement can be severe. If possible, we recommend that isolated pad footings structurally connected to other foundation elements be avoided and that the foundation system be designed as rigid as is reasonably possible. Careful preparation of the support soils, placement of granular compacted structural fill, careful placement and compaction of stem wall backfill and positive surface drainage adjacent to the foundation system all help reduce the influence of movement within the foundation support soils on the performance of the spread footing foundation system. We recommend that the footings be supported by a layer of moisture conditioned and compacted natural soil which is overlain by a layer of compacted structural fill material. This concept is outlined below; The foundation excavation should be excavated to at least one (1) foot below the proposed footing support elevation. The natural soils exposed in the bottom of the excavation should be scarified to a depth of about six (6) to eight (8) inches The scarified soil should be thoroughly moisture conditioned to about two (2) percent above the laboratory determined optimum moisture content and then compacted. After completion of the compaction of the moisture conditioned natural soil a one (1) foot thick layer of granular aggregate base course structural fill material should be placed, moisture conditioned and compacted. The moisture conditioned natural soil material and the granular soils should be compacted as discussed under the Compaction Recommendations portion of this report, below. All footings should have a minimum depth of embedment of at least one (1) foot. Exterior footings should have a minimum depth of embedment at least equal to the code frost depth. The embedment concept is shown below. 20

22 Minimum depth of embedment Footing Footing Embedment Concept No Scale Spread footings located away from sloped areas may be designed using the allowable gross bearing capacity values tabulated below. Minimum Depth of Embedment (Feet) Continuous Footing Design Capacity (psf) 1 1,500 2, ,000 2, ,500 3,000 Isolated Footing Design Capacity (psf) The bearing capacity values tabulated above may be increased by twenty (20) percent for transient conditions associated with wind and seismic loads. Snow loads are not transient loads. The bearing capacity values above are based on a continuous spread footing width in the range of about two (2) to three (3) feet and an isolated footing width in the range of about three (3) to four (4) feet. Larger footings and/or footings placed on deeper depth of compacted structural fill will have a higher design soil bearing capacity. Development of the final footing design width is usually an iterative process based on evaluation of design pressures, footing widths and the thickness of compacted structural fill beneath the footings. We should be contacted as the design process continues to re-evaluate the design capacities above based on the actual proposed footing geometry. 21

23 The settlement of the spread footing foundation system will be influenced by the footing size and the imposed loads. We estimated the total post construction settlement of the footings based on our laboratory consolidation data, the type and size of the footing. Our analysis below assumed that the highest bearing capacity value tabulated above was used in the design of the footings. The amount of post construction settlement may be reduced by placing the footings on a blanket of compacted structural fill material. The estimated settlement for continuous footing with a nominal width of about two (2) to three (3) feet are tabulated below Thickness of Compacted Estimated Settlement Structural Fill (feet) (inches) B/2 1/2-3/4 B About 1/2 B is the footing width The estimated settlement for isolated pad footings with a nominal square dimension of about three (3) to four (4) feet are tabulated below Thickness of Compacted Estimated Settlement Structural Fill (feet) (inches) B/2 3/4-1 3B/4 1/2-3/4 B is the footing width The compacted structural fill should be placed and compacted as discussed in the Construction Considerations, Fill Placement Recommendations section of this report, below. The zone of influence of the footing (at elevations close to the bottom of the footing) is often approximated as being between two (2) lines subtended at 45 degree angles from each bottom corner of the footing. The compacted structural fill should extend beyond the zone of influence of the footing as shown in the sketch below. 22

24 Footing Zone of Influence Concept Footing 45 degrees 45 degrees Footing Zone of Influence No Scale A general and simple rule to apply to the geometry of the compacted structural fill blanket is that it should extend beyond each edge of the footing a distance which is equal to the fill thickness. All footings should be support at an elevation deeper than the maximum depth of frost penetration for the area. This recommendation includes exterior isolated footings and column supports. We understand that the code frost depth for the City of Cortez is thirty-two (32) inches. The post construction differential settlement may be reduced by designing footings that will apply relatively uniform loads on the support soils. Concentrated loads should be supported by footings that have been designed to impose similar loads as those imposed by adjacent footings. Under no circumstances should any footing be supported by more than three (3) feet of compacted structural fill material unless we are contacted to review the specific conditions supporting these footing locations. The design concepts and parameters presented above are based on the soil conditions encountered in our test borings. We should be contacted during the initial phases of the foundation excavation at the site to assess the soil support conditions and to verify our recommendations. 23

25 5.3 General Shallow Foundation Considerations Some movement and settlement of any shallow foundation system will occur after construction. Movement associated with swelling soils also occurs occasionally. Utility line connections through and foundation or structural component should be appropriately sleeved to reduce the potential for damage to the utility line. Flexible utility line connections will further reduce the potential for damage associated with movement of the structure. 6.0 RETAINING STRUCTURES Laterally loaded walls will be constructed as part of this site development. We understand that both interior structure retaining walls associated with the main structure as well as exterior retaining walls will be constructed. The magnitude of the lateral earth pressure forces is partially dependent on the soil strength characteristics, the geometry of the ground surface adjacent to the retaining structure, the subsurface water conditions and on surcharge loads. The retaining structures may be designed using the following un-factored equivalent fluid pressure values tabulated below for level backfill. We are available to provide specific analysis for retaining walls that will have sloped backfill or surcharge loads above the retained soil mass. Type of Lateral Earth Pressure Level Native Sandy Clay Soil Backfill (pounds per cubic foot/foot)* Lateral Earth Pressure Values Level Granular Soil Backfill (pounds per cubic foot/foot) Active At-rest Passive Allowable Coefficient of Friction 0.35 (sandy clay soils) 0.45 (imported structural fill) The passive wedge of backfill material and retained soil materials should be compacted to at least ninety (90) percent of the maximum dry density as defined by ASTM D1557, Modified Proctor, in order to achieve the values tabulated above. The table below provides estimated for the magnitude of retaining wall rotation/translation to achieve the active and passive pressures tabulated above. 24

26 Backfill Soil Type Displacement to achieve active pressures (per total unit height of wall) Displacement to achieve passive pressures (per total unit height of wall) Native sandy clay soils Imported Granular Fill Granular soil that is used for the retaining wall backfill may be permeable and may allow water migration to the foundation support soils. We recommend capping the granular backfill material with about one and one-half (1½) to two (2) feet of the site clay soil materials. A separation geotextile may be necessary depending on the grading of the granular backfill materials. It should be noted that if the site clay soils are used settlement may occur in the backfill mass which will influence the performance of overlying concrete flatwork or structural components. Utilizing a granular fill material will decrease the overall consolidation of the backfill mass. This is discussed in more detail in Section 8.0 below. The values tabulated above are for well drained backfill soils. The values provided above do not include any forces due to adjacent surcharge loads or sloped soils. If the backfill soils become saturated the imposed lateral earth pressures will be significantly higher than those tabulated above. The granular imported soil backfill values tabulated above are appropriate for material with an angle of internal friction of thirty-five (35) degrees, or greater. The granular backfill must be placed within the retaining structure zone of influence as shown below in order for the lateral earth pressure values tabulated above for the granular material to be appropriate. 25

27 Retaining wall zone of influence Retaining Structure 55 Degrees Impervious soil backfill for upper 2 feet Retaining Structure Zone of Influence Concept, No Scale If a granular backfill is chosen it should not extend to the ground surface. Some granular soils allow ready water migration which may result in increased water access to the foundation soils. The upper few feet of the backfill should be constructed using an impervious soil such as siltyclay and clay soils from the project site. Backfill should not be placed and compacted behind the retaining structure unless approved by the project structural engineer. Backfill placed prior to construction of all appropriate structural members such as floors, or prior to appropriate curing of the retaining wall concrete (if used) may result in severe damage and/or failure of the retaining structure. 7.0 SUBSURFACE DRAIN SYSTEM A subsurface drain system must be constructed near the base of all retaining walls. Exterior retaining structures may be constructed with weep holes to allow subsurface water migration through the retaining structures. As discussed earlier in this report, we feel that it is feasible for a temporary subsurface water condition to develop over the relatively shallow formational materials that underlie the project site during periods of heavy precipitation or snow melt. Due to the basement areas that will be incorporated with the structure we recommend that in addition to the basement retaining wall drain system, a subsurface drain system be constructed adjacent to the exterior sides of the structure. It may be possible to terminate the drain system along portions of the downslope side of the structure such as along the north side of the structure to facilitate daylighting the drain 26

28 system. We suggest that the system consist of a fabric-wrapped aggregate, or a sand material (some sands may not need fabric, we are available to discuss this with you) which surrounds a rigid perforated pipe. We typically do not recommend use of flexible corrugated perforated pipe since it is not readily possible to establish a uniform gradient of the flexible pipe throughout the drain system alignment. Corrugated drain tile is perforated throughout the entire circumference of the pipe and therefore water can escape from the perforations at undesirable locations after being collected. The nature of the perforations of the corrugated material further decreases its effectiveness as a subsurface drain conduit. The drain system pipe should be graded to surface outlets if possible. In areas where this is not possible a sump vault may be constructed. Typically a minimum gradient of about two (2) percent is preferred for subsurface drain systems, but site geometry and topography may influence the actual installed pipe gradient. Water must not be allowed to pool along any portion of the subsurface drain system. An improperly constructed subsurface drain system may actually promote water access to undesirable locations. The drain system pipe should be surrounded by about two (2) to four (4) cubic feet per lineal foot of free draining aggregate or sand. If a sump vault and pump are incorporated into the subsurface drain system, care should be take so that the water pumped from the vault does not recirculate through pervious soils and obtain access to other portions of the structure. A generalized subsurface drain system concept is shown below. Retaining or foundation wall Water proof membrane or similar placed on the foundation wall and extending below outer face of footing Pervious drain board or fabric (optional) Footing 27 Geotextile filter fabric, if appropriate Impervious backfill for upper 2 feet Compacted backfill that meets lateral earth pressure design criteria. Perforated pipe surrounded by fabric wrapped free-draining material. Note: The elevation of the pipe will depend on the location in the system at which the cross section is considered. Subsurface Drain System Concept No Scale

29 There are often aspects of each site and structure which require some tailoring of the subsurface drain system to meet the needs of individual projects. We are available to provide consultation for the subsurface drain system for this project, if desired. Water often will migrate along utility trench excavations in formational material. If the utility trench extends from areas above the site, this trench may be a source for subsurface water to access the structure. We suggest that the utility trench backfill be thoroughly compacted to help reduce the amount of water migration. 8.0 CONCRETE FLATWORK We understand that both interior and exterior concrete flatwork will be included in the project design. Concrete flatwork is typically lightly loaded and has a limited capability to resist shear forces associated with movement within the support soils. It is prudent for the design and construction of concrete flatwork on this project to be able to accommodate some movement associated with movement (likely primarily consolidation) of the support soils. Of particular concern for this project, partially due to our understanding of the basement wall heights, is post construction consolidation of the basement/corridor retaining wall backfill and supported slab-on-grade floors. We anticipate that an average percent consolidation of about 1.0 percent may occur in the native sandy clay soils, and an average percent consolidation of about 0.03 percent consolidation may occur in an imported granular fill material, even if these materials are thoroughly compacted. For example, for a fifteen (15) foot backfill height, we anticipate that up to about 1.5 inches of settlement may occur in the retaining wall backfill if the native sandy clay soil materials are used, and about one-half (1/2) inch of settlement may occur if a well compacted granular fill material is used. These are estimated values. For this reason we suggest that at minimum a granular backfill material be used for the basement/corridor retaining walls. Since at least portions of the main level floor system will be structurally supported, it may be prudent to explore structurally supporting the entire main floor system that will be located over the retaining wall backfill materials. 8.1 Interior Concrete Slab-on-Grade Floors A primary goal in the design and construction of interior concrete slab-on-grade floors is to reduce the amount of post construction movement that may occur in concrete slab-on-grade floors due to movement of the support soils. A parallel goal is to reduce the potential for damage to the structure associated with any movement of the slab-on-grade which may occur. There are limited options available to help mitigate the influence of volume changes in the support soil for concrete slab-on-grade floors, these include; 28

30 Preconstruction scarification, moisture conditioning and re-compaction of the natural soils in areas proposed for support of concrete flatwork, and/or, Placement and compaction of granular compacted structural fill material. Damage associated with movement of interior concrete slab-on-grade floor can be reduced by designing the floors as floating slabs. Floating concrete slabs are not structurally tied to the foundations or the overlying structure. Interior walls or columns should not be supported on the interior floor slabs. Movement of interior walls or columns due to movement in the floor slab can cause severe damage throughout the structure. Interior walls may be structurally supported from framing above the floor, or interior walls and support columns may be supported on interior portions of the foundation system. The only means to completely mitigate the influence of volume changes on the performance of interior floors is to structurally support the floors. Floors that are suspended by the foundation system will not be influenced by volume changes in the site soils. The suggestions and recommendations presented below are intended to help reduce the influence of volume changes in the support soils on the performance of the concrete slab-on-grade floors. Interior concrete slab-on-grade floors may be supported by a composite fill blanket which is composed of a six (6) inch thick lower layer of scarified, moisture conditioned natural soil that is overlain by a twelve (12) inch thick blanket of compacted structural fill. The scarified fill material and the compacted structural fill material should be constructed as discussed under the Construction Considerations, Fill Placement Considerations section of this report below. Capillary and vapor moisture rise through the slab support soil may provide a source for moisture in the concrete slab-on-grade floor. This moisture may promote development of mold or mildew in poorly ventilated areas and may influence the performance of floor coverings and mastic placed directly on the floor slabs. There are a few options available to help reduce the migration of capillary moisture and vapor rise into the floor slab. Comments for Reduction of Capillary Rise One option to stop capillary rise through the floor slab is to place a layer of clean aggregate material, such as washed concrete aggregate for the upper four (4) to six (6) inches of fill material supporting the concrete slabs. Comments for Reduction of Vapor Rise To reduce vapor rise through the floors slab a moisture barrier such as a 6 mil (or thicker) plastic, or similar impervious geotextile material may be placed below the floor slab. The 29

31 American Concrete Institute (ACI) recommends that four (4) inches of trimmable material (not sand) conforming to ASTM D448, No.10 grading be used between the vapor barrier and the overlying concrete for support of concrete slab-on-grade floors. We have provided the specifications for ASTM D48 No.10 Sand below. Grading of ASTM D448 No. 10 Material Sieve Size Percent Passing Each Sieve 3/8 inch 100 # # This type of material may not be locally available therefore we suggest that if an impervious barrier is used that it should be placed on at two (2) to three (3) inches of fine-grained granular material, such as crusher reject material to protect it from punctures from the underlying substrate materials with at least four (4) inches of trimmable material closely conforming to the D448 No. 10 grading, such as appropriately graded crusher reject material, on top of the barrier to support the concrete floor slab. This will help reduce the influence of the barrier on the migration of concrete bleed water and associated concrete curing conditions during construction of the slab. There are proprietary barriers that are puncture resistant that may not need the underlying layer of protective material. We do not recommend placement of the concrete directly on a moisture barrier unless the concrete contractor has had previous experience with curing of concrete placed in this manner. The project architect, designer and/or builder should be contacted for the best capillary break for this project. The project architect, designer and/or builder should be contacted for the best capillary break for this project. It is not necessary, from a geotechnical engineering perspective, to install capillary breaks under garage floors unless it is possible that future conversion of the garage into interior rooms is planned. The project structural engineer should be contacted to provide steel reinforcement design considerations for the proposed floor slabs. Any steel reinforcement placed in the slab should be placed at the appropriate elevations to allow for proper interaction of the reinforcement with tensile stresses in the slab. Reinforcement steel that is allowed to cure at the bottom of the slab will not provide adequate reinforcement. 8.2 Exterior Concrete Flatwork Considerations Exterior concrete flatwork includes concrete driveway slabs, aprons, patios, and walkways. The desired performance of exterior flatwork typically varies depending on the proposed use of the 30

32 site and each owner s individual expectations. As with interior flatwork, exterior flatwork is particularly prone to movement and potential damage due to movement of the support soils. This movement and associated damage may be reduced by following the recommendations discussed under interior flatwork, above. Unlike interior flatwork, exterior flatwork may be exposed to frost heave. If some movement of exterior flatwork is acceptable, we suggest that the support areas be prepared by scarification, moisture conditioning and re-compaction of about four (4) inches of the natural soils followed by placement of about four (4) to six (6) inches of compacted granular fill material. The scarified material and granular fill materials should be placed as discussed under the Construction Considerations, Fill Placement Recommendations section of this report, below. It is important that exterior flatwork be separated from exterior column supports, masonry veneer, finishes and siding. No support columns, for the structure or exterior decks, should be placed on exterior concrete unless movement of the columns will not adversely affect the supported structural components. Movement of exterior flatwork may cause damage if it is in contact with portions of the structure exterior. Exterior flatwork should not be placed on soils prepared for support of landscaping vegetation. Cultivated soils will not provide suitable support for concrete flatwork. 8.3 General Concrete Flatwork Comments It is relatively common that both interior and exterior concrete flatwork is supported by areas of fill adjacent to either shallow foundation walls or basement retaining walls. A typical sketch of this condition is shown below. 31

33 Foundation or retaining wall Concrete Slab-on-grade Limit of construction excavation Wall backfill area Wall Backfill and Slab Support Sketch No Scale Settlement of the backfill shown above will create a void and lack of soil support for the portions of the slab over the backfill. Settlement of the fill supporting the concrete flatwork is likely to cause damage to the slab-on-grade. Settlement and associated damage to the concrete flatwork may occur when the backfill is relatively deep, even if the backfill is compacted. If this condition is likely to exist on this site it may be prudent to design the slab to be structurally supported on the retaining or foundation wall and designed to span to areas away from the backfill area as designed by the project structural engineer. We are available to discuss this with you. 9.0 PAVEMENT SECTION THICKNESS DESIGN RECOMMENDATIONS We performed a California Bearing Ratio (CBR) test on a composite sample of soil obtained from the project site. Based on the results of the CBR test we used an R-Value of 6 in our analysis for the pavement section thickness design. We recommend that the subgrade soils be proof-rolled prior to the scarification and processing operations. Any soft areas observed during the proof-rolling operations should be removed and replaced with properly processed materials and/or granular aggregate materials as part of the subgrade preparation. The site subgrade pavement section support soils must be scarified to a depth of six (6) inches, moisture conditioned and compacted prior to placement of the overlying aggregate pavement 32

34 section materials. The material should be moisture conditioned to within about two (2) percent of the optimum moisture content and compacted to at least ninety (90) percent of maximum dry density as determined by the modified Proctor test, ASTM D1557. The surface of the subgrade soil should be graded and contoured to be approximately parallel to the finished grade of the pavement surface. The aggregate materials used within the pavement section should conform to the requirements outlined in the current Specifications for Road and Bridge Construction, Colorado Department of Transportation (CDOT). The aggregate base material should be a three-quarter (3/4) inch minus material that conforms to the CDOT Class 6 aggregate base course specifications and have an R- value of at least 78. The aggregate sub-base course should conform to the CDOT specifications for Class 2 material and should have a minimum R-value 70. Other material may be suitable for use in the pavement section, but materials different than those listed above should be tested and observed by us prior to inclusion in the project design or construction. Aggregate sub-base and base-course materials should be compacted to at least ninety-five (95) percent of maximum dry density as defined by the modified Proctor test, ASTM D1557. Aggregate base-course and sub-base course locally available that do not meet the above specifications may be suitable for this project. We are available to review other aggregate gradations produced by local gravel producers to insure the suitability of the gravel products for the project. The aggregate base course should have a minimum R-value of 72, and the aggregate sub-base course should have a minimum R-Value of Asphalt Pavement Recommendations We recommend that the asphalt concrete used on this project be mixed in accordance with a design prepared by a licensed professional engineer, or an asphalt concrete specialist. We should be contacted to review the mix design prior to placement at the project site. We recommend that the asphalt concrete be compacted to between ninety-two (92) and ninety-six (96) percent of the maximum theoretical density. We have provided several pavement section design thicknesses below. The structural support characteristics of each section are approximately equal. The project civil engineer, or contractor can evaluate the best combination of materials for economic considerations. We have provided pavement section thicknesses for both 50,000 (standard vehicle use section) and 125,000 (heavy vehicle use section)- 18,000 pound equivalent single axle loads (18k ESAL). We are available to provide additional design sections, if these are desired. 33

35 Pavement Section Design Thickness Light Duty Standard Passenger Car/Truck Use 50,000 18k ESAL Pavement Section Component Alternative Thicknesses of Each Component (inches) Asphalt Concrete 3 3 Class Class Reconditioned Subgrade 6 6 Pavement Section Design Thickness Heavy Vehicle Use 125,000 18k ESAL Pavement Section Component Alternative Thicknesses of Each Component (inches) Asphalt Concrete Class Class Reconditioned Subgrade The pavement section thicknesses tabulated above are appropriate for the post-construction traffic use associated with the fire station. Heavy construction equipment traffic will have a significant influence on the quality, character, and design life of the pavement sections tabulated above. If possible we recommend that the asphalt pavement not be placed until completion of the major construction activity. We are available to discuss this with you as the project progresses. 9.2 Rigid Concrete Pavement Recommendations We anticipate that rigid concrete pavement will likely be used for portions of the project including exterior aprons, and possibly exterior driveway/parking areas. The following recommendations are based on the American Concrete Institute (ACI) Guide for Design and Construction of Concrete Parking Lots report 330R-01, strength characteristics (CBR-value) of the native subgrade soils, and on our experience with concrete paved parking lots in the region. A modulus of subgrade reaction of 150 pounds per cubic inch may be used for design purposes. 34

36 Our recommendations are as follows; For the proposed main parking area that will service light vehicular traffic only, a minimum concrete mat thickness of five (5) inches should be used. This section is valid for an average daily truck (ADTT) of less than ten (10). For areas that will be exposed to heavy truck traffic on a regular basis a minimum concrete mat thickness of six (6) inches should be used. The concrete mat should be supported by a minimum thickness of six (6) inches of three-quarter (3/4) inch minus aggregate base course material that meets the specifications tabulated in section 9.1 above. We are available to review aggregate gradations produced by local gravel producers to insure the suitability of the gravel products for the project. The aggregate materials should be compacted to at least ninety-five (95) percent of maximum dry density as defined by AASHTO T-180 or ASTM D 1557, Modified Proctor test. The upper six (6) inches of subgrade support soils should be scarified and compacted to at least ninety (90) percent of maximum dry density as defined by AASHTO T-180 or ASTM D1557, Modified Proctor test prior to placement of the aggregate base course. A concrete with a minimum twenty-eight (28) day compressive strength of 4,500 pounds per square inch (psi) should be used. Joint spacing should not exceed twelve and one-half (12½) feet for a slab thickness of five (5) inches and should not exceed fifteen (15) feet for a slab thickness of six (6) inches. The recommendations for minimum concrete strength presented here are based on the ACI recommendations. The site specific structural engineering design recommendations should take precedent over those listed in this report. The project structural engineer should be contacted for steel reinforcement design. We are available to discuss our recommendations with the project structural engineer as needed. 9.3 General Parking Area Considerations Water intrusion into the pavement section support materials will negatively influence the performance of the parking lot surface. Water from irrigation, water from natural sources that migrates into the soils beneath landscapes surface and water from any source that gains access to the support materials can all decrease the life of the parking lot surface. Care should be taken along curbs and any edge of the parking lot to develop an interface between the material that will reduce subsurface and surface water migration into the support soil and pavement section materials. Landscape islands and other irrigated features often promote water migration since no surface flow from these features typically occurs. The same can occur along perimeter cub areas. 35

37 Water will often migrate along the interface of concrete curbs and gutter areas early in the life of any parking area. The tendency for this type of migration often decreases with time, but can be reduced by compaction of materials along the outside base of curb areas adjacent to the interface of the concrete curb and the underlying soil prior to placement of landscaping soil above this interface CONSTRUCTION CONSIDERATIONS This section of the report provides comments, considerations and recommendations for aspects of the site construction which may influence, or be influenced by the geotechnical engineering considerations discussed above. The information presented below is not intended to discuss all aspects of the site construction conditions and considerations that may be encountered as the project progresses. If any questions arise as a result of our recommendations presented above, or if unexpected subsurface conditions are encountered during construction we should be contacted immediately Fill Placement Recommendations There are several references throughout this report regarding both natural soil and compacted structural fill recommendations. The recommendations presented below are appropriate for the fill placement considerations discussed throughout the report above. All areas to receive fill, structural components, or other site improvements should be properly prepared and grubbed at the initiation of the project construction. The grubbing operations should include scarification and removal of organic material and soil. No fill material or concrete should be placed in areas where existing vegetation or fill material exist Natural Soil Fill Any natural soil used for any fill purpose should be free of all deleterious material, such as organic material and construction debris. Natural soil fill includes excavated and replaced material or in-place scarified material. The natural soils should be moisture conditioned, either by addition of water to dry soils, or by processing to allow drying of wet soils. The proposed fill materials should be moisture conditioned to between about optimum and about two (2) percent above optimum soil moisture content. This moisture content can be estimated in the field by squeezing a sample of the soil in the palm of the hand. If the material easily makes a cast of soil which remains in-tact, and a minor amount of surface moisture develops on the cast, the material is close to the desired 36

38 moisture content. Material testing during construction is the best means to assess the soil moisture content. Moisture conditioning of clay or silt soils may require many hours of processing. If possible, water should be added and thoroughly mixed into fine grained soil such as clay or silt the day prior to use of the material. This technique will allow for development of a more uniform moisture content and will allow for better compaction of the moisture conditioned materials. The moisture conditioned soil should be placed in lifts that do not exceed the capabilities of the compaction equipment used and compacted to at least ninety (90) percent of maximum dry density as defined by ASTM D1557, modified Proctor test. We typically recommend a maximum fill lift thickness of six (6) inches for hand operated equipment and eight (8) to ten (10) inches for larger equipment. Care should be exercised in placement of utility trench backfill so that the compaction operations do not damage the underlying utilities. Typically the maximum lift thickness is about six (6) to eight (8) inches, therefore the maximum allowable rock size for natural soil fill is about six (6) inches. If smaller compaction equipment is being used, such as walk behind compactors in trenches, the maximum rock size should be less than about three (3) inches Granular Compacted Structural Fill Granular compacted structural fill is referenced in numerous locations throughout the text of this report. Granular compacted structural fill should be constructed using an imported commercially produced rock product such as aggregate road base. Many products other than road base, such as clean aggregate or select crusher fines may be suitable, depending on the intended use. If a specification is needed by the design professional for development of project specifications, a material conforming to the Colorado Department of Transportation (CDOT) Class 6 aggregate road base material can be specified. This specification can include an option for testing and approval in the event the contractor s desired material does not conform to the Class 6 aggregate specifications. We have provided the CDOT Specifications for Class 6 material below Grading of CDOT Class 6 Aggregate Base-Course Material Sieve Size Percent Passing Each Sieve ¾ inch 100 # # # Liquid Limit less than 30 37

39 All compacted structural fill should be moisture conditioned and compacted to at least ninety (90) percent of maximum dry density as defined by ASTM D1557, modified Proctor test. Areas where the structural fill will support traffic loads under concrete slabs or asphalt concrete should be compacted to at least ninety-five (95) percent of maximum dry density as defined by ASTM D1557, modified Proctor test. Although clean-screened or washed aggregate may be suitable for use as structural fill on sites with sand or non-expansive silt soils, or on sites where shallow subsurface water is present, clean aggregate materials must not be used on any site where expansive soils exist due to the potential for water to accumulate in the voids of the clean aggregate materials. Clean aggregate fill, if appropriate for the site soil conditions, must not be placed in lifts exceeding eight (8) inches and each lift should be thoroughly vibrated, preferably with a platetype vibratory compactor prior to placing overlying lifts of material or structural components. We should be contacted prior to the use of clean aggregate fill materials to evaluate their suitability for use on this project Excavation Considerations Unless a specific classification is performed, the site soils should be considered as an Occupational Safety and Health Administration (OSHA) Type C soil and should be sloped and/or benched according to the current OSHA regulations. Excavations should be sloped and benched to prevent wall collapse. Any soil can release suddenly and cave unexpectedly from excavation walls, particularly if the soils is very moist, or if fractures within the soil are present. Daily observations of the excavations should be conducted by OSHA competent site personnel to assess safety considerations. We did not encounter free subsurface water in our test borings at the depths that we anticipate the project excavation will extend. If water is encountered during construction, it may be necessary to dewater excavations to provide for suitable working conditions. We encountered formational material in our test borings. We suspect that it may be difficult to excavate this material using conventional techniques. If blasting is planned it must be conducted strategically to reduce the affect of the blasting on the support characteristics of the site materials and the stability of adjacent slopes. We typically recommend that where possible blasting be avoided, however blasting is often needed to aid in the excavation of the site to develop the desired footing support elevations. It is typical to have about two (2) to three (3) feet of loose angular clasts of rock, commonly called shot-rock below the desired bottom of excavation elevations. This material is not suitable for support of structural components and should be removed and replaced with compacted structural fill in areas proposed for support of structural 38

40 components. If possible excavations should be constructed to allow for water flow from the excavation the event of precipitation during construction. If this is not possible it may be necessary to remove water from snowmelt or precipitation from the foundation excavations to help reduce the influence of this water on the soil support conditions and the site construction characteristics Excavation Cut Slopes We anticipate that some permanent excavation cut slopes may be included in the site development. Temporary cut slopes should not exceed five (5) feet in height and should not be steeper than about one to one (1:1, horizontal to vertical) for most soils. Permanent cut slopes of greater than five (5) feet or steeper than two and one-half to one (2½:1, h:v) must be analyzed on a site specific basis Utility Considerations Subsurface utility trenches will be constructed as part of the site development. Utility line backfill often becomes a conduit for post construction water migration. If utility line trenches approach the proposed project site from above, water migrating along the utility line and/or backfill may have direct access to the portions of the proposed structure where the utility line penetrations are made through the foundation system. The foundation soils in the vicinity of the utility line penetration may be influenced by the additional subsurface water. There are a few options to help mitigate water migration along utility line backfill. Backfill bulkheads constructed with high clay content soils and/or placement of subsurface drains to promote utility line water discharge through the foundation drain system. Some movement of all structural components is normal and expected. The amount of movement may be greater on sites with problematic soil conditions. Utility line penetrations through any walls or floor slabs should be sleeved so that movement of the walls or slabs does not induce movement or stress in the utility line. Utility connections should be flexible to allow for some movement of the floor slab. If utility line trenches are excavated using blasting techniques it is relatively common for surface and subsurface water to migrate along the fractures in the rock that may be created by blasting. If this water gains access to a utility line trench that has a gradient down toward the structure the water may gain access to the foundation support materials and/or subsurface portions of the proposed structure. Provisions should be made in the project construction plans to create an impervious barrier to prevent water from migrating into undesirable locations. 39

41 10.4 Exterior Grading and Drainage Comments The ground surface adjacent to the structure should be sloped to promote water flow away from the foundation system and flatwork. Snow storage areas should not be located in areas which will allow for snowmelt water access to support soils for the foundation system or flatwork. Water flow from the roof of the structure should be captured and directed away from the structure. If the roof water is collected in an eave gutter system, or similar, the discharge points of the system must be located away from areas where the water will have access to the foundation backfill or any structure support soils. If downspouts are used, provisions should be made to either collect or direct the water away from the structure. The project civil engineering consultant or builder should develop a drainage scheme for the site. We typically suggest a minimum fall of about eight (8) to ten (10) percent away from the structure, in the absence of design criteria from others. Care should be taken to not direct water onto adjacent property or to areas that would negatively influence existing structures or improvements Landscaping Considerations We recommend against construction of landscaping which requires excessive irrigation. Generally landscaping which uses abundant water requires that the landscaping contractor install topsoil which will retain moisture. The topsoil is often placed in flattened areas near the structure to further trap water and reduce water migration from away from the landscaped areas. Unfortunately almost all aspects of landscape construction and development of lush vegetation are contrary to the establishment of a relatively dry area adjacent to the foundation walls. Excess water from landscaped areas near the structure can migrate to the foundation system or flatwork support soils, which can result in volume changes in these soils. A relatively common concept used to collect and subsequently reduce the amount of excess irrigation water is to glue or attach an impermeable geotextile fabric or heavy mill plastic to the foundation wall and extend it below the topsoil which is used to establish the landscape vegetation. A thin layer of sand can be placed on top of the geotextile material to both protect the geotextile from punctures and to serve as a medium to promote water migration to the collection trench and perforated pipe. The landscape architect or contractor should be contacted for additional information regarding specific construction considerations for this concept which is shown in the sketch below. 40

42 Foundation Wall Perforated pipe surrounded by freedraining material Approximate limit foundation excavation backfill Impermeable geotextile material, lapped and glued to the foundation wall above grade Filter Fabric Shallow Landscaping Drain Concept No Scale 41

43 A free draining aggregate or sand may be placed in the collection trench around the perforated pipe. The perforated pipe should be graded to allow for positive flow of excess irrigation water away from the structure or other area where additional subsurface water is undesired. Preferably the geotextile material should extend at least ten (10) or more feet from the foundation system. Care should be taken to not place exterior flatwork such as sidewalks or driveways on soils that have been tilled and prepared for landscaping. Tilled soils will settle which can cause damage to the overlying flatwork. Tilled soils placed on sloped areas often creep down-slope. Any structure or structural component placed on this material will move down-slope with the tilled soil and may become damaged Soil Sulfate Content, Corrosion Issues The requested scope of our services did not include assessment of the chemical constituents of corrosion potential of the site soils. Most soils in southwest Colorado are not typically corrosive to concrete. There has not been a history of damage to concrete due to sulfate corrosion in the area. We are available to perform soluble sulfate content tests to assess the corrosion potential of the soils on concrete if desired Radon Issues The requested scope of service of this report did not include assessment of the site soils for radon production. Many soils and formational materials in western Colorado produce Radon gas. The structure should be appropriately ventilated to reduce the accumulation of Radon gas in the structure. Several Federal Government agencies including the Environmental Protection Agency (EPA) have information and guidelines available for Radon considerations and home construction. If a radon survey of the site soils is desired, please contact us CONSTRUCTION MONITORING AND TESTING Construction monitoring including engineering observations and materials testing during construction is a critical aspect of the geotechnical engineering contribution to any project. Unexpected subsurface conditions are often encountered during construction. The site foundation excavation should be observed by the geotechnical engineer or a representative during the early stages of the site construction to verify that the actual subsurface soil and water conditions were properly characterized as part of field exploration, laboratory testing and engineering analysis. If 42

44 the subsurface conditions encountered during construction are different than those that were the basis of the geotechnical engineering report then modifications to the design may be implemented prior to placement of fill materials or foundation concrete. Compaction testing of fill material should be performed throughout the project construction so that the engineer and contractor may monitor the quality of the fill placement techniques being used at the site. Generally we recommend that compaction testing be performed for any fill material that is placed as part of the site development. Compaction tests should be performed on each lift of material placed in areas proposed for support of structural components. In addition to compaction testing we recommend that the grain size distribution, clay content and swell potential be evaluated for any imported materials that are planned for use on the site. Concrete tests should be performed on foundation concrete and flatwork. If asphaltic concrete is placed for driveways or aprons near the structure we are available to provide testing of these materials during placement. We are available to develop a testing program for soil, aggregate materials, concrete and asphaltic concrete for this project CONCLUSIONS AND CONSIDERATIONS The information presented in this report is based on our understanding of the proposed construction that was provided to us and on the data obtained from our field and laboratory studies. We recommend that we be contacted during the design and construction phase of this project to aid in the implementation of our recommendations. Please contact us immediately if you have any questions, or if any of the information presented above is not appropriate for the proposed site construction. The recommendations presented above are intended to be used only for this project site and the proposed construction which was provided to us. The recommendations presented above are not suitable for adjacent project sites, or for proposed construction that is different than that outlined for this study. Our recommendations are based on limited field and laboratory sampling and testing. Unexpected subsurface conditions encountered during construction may alter our recommendations. We should be contacted during construction to observe the exposed subsurface soil conditions to provide comments and verification of our recommendations. We are available to review and tailor our recommendations as the project progresses and additional information which may influence our recommendations becomes available. 43

45 Please contact us if you have any questions, or if we may be of additional service. Respectfully submitted, TRAUTNER GEOTECH Jonathan P. Butler, P.E. Staff Geotechnical Engineer 44