Subsurface Exploration and Geotechnical Evaluation Hotel at Burnet Road (MoPac) Austin, Texas. Prepared for: Visvanath, LP 3120 Montopolis Drive

Transcription

1 Nicholas F. Kauffman, M.S., P.E. Principal Geotechnical Engineer Subsurface Exploration and Geotechnical Evaluation Hotel at Burnet Road (MoPac) Austin, Texas Prepared for: Visvanath, LP 3120 Montopolis Drive Austin, Texas Prepared by: Capital Geotechnical Services PLLC Cedar Park, Texas Texas Engineering Firm Registration # 9458 Capital Geotechnical Services Project # November 1, 2015

2 Hotel at Burnet Road (MoPac), Austin, Texas Capital Geotechnical Services Project # TABLE OF CONTENTS Page: SCOPE... 1 SUMMARY... 1 SITE LOCATION AND CONDITIONS... 3 LANDFILL LITERATURE REVIEW... 3 PROPOSED DEVELOPMENT AND CONSTRUCTION... 4 GEOLOGY AND SOIL MAPPING INFORMATION... 4 SUBSURFACE EXPLORATION... 5 LABORATORY TESTING... 5 SUBSURFACE CONDITIONS... 6 POTENTIAL MOVEMENT OF THE CLAY SOILS... 7 SITE PREPARATION AND EARTHWORK... 8 FOUNDATIONS Drilled Pier Option Stiffened Slab Option Driven Steel Pipe Piles STRUCTURALLY SUPPORTED SLAB (if used) SEISMIC DESIGN PAVEMENT THICKNESS DESIGN CONCRETE PAVEMENT COMMENTARY PAVEMENT MAINTENANCE PAVEMENT MATERIAL RECOMMENDATIONS AND TESTING SURFACE DRAINAGE, VEGETATION, AND UTILITY CONNECTIONS POST-TENSIONING (IF USED) LIMITATIONS INSPECTIONS FIGURES: Figure 1: Vicinity Map Figure 2: Local Lot Plan Figure 3: Geology Map Figure 4: Approximate Locations of Exploratory Borings Figure 5 to Figure 8: Boring Logs Figure 9: Standard Reference Notes for Boring Logs Figures 10 and 11: Swell Test Results Figure 12: City of Austin Landfill Check Form

3 SCOPE This report presents the results of a geotechnical evaluation for a proposed 3-story hotel building on the northbound frontage road of the MoPac Expressway in Austin, Texas. This study was performed to evaluate subsurface conditions and to provide recommendations for the design and construction of the foundation system and for pavement thickness design. Capital Geotechnical Services PLLC performed this subsurface exploration and geotechnical evaluation in accordance with our proposal # P authorized (signed) on September 17, The scope of services for this study included the determination of subsurface conditions through field and laboratory testing, an evaluation of the subsurface conditions relative to the proposed construction, and the preparation of a geotechnical report. This report includes results, evaluations, and recommendations concerning earthwork, foundations, groundwater, pavement, quality control testing, and other geotechnical related aspects of the project. A summary of our conclusions is presented in the following section of this report. More complete descriptions and findings of our field and laboratory testing are presented in the rest of the report. The scope of services did not include any environmental site assessments (ESAs) for the presence or absence of wetland or hazardous or toxic materials in the soil, air, surface water, or groundwater at this site. SUMMARY The subsurface conditions encountered during our exploration and our geotechnical engineering evaluations and recommendations are summarized in the following paragraphs. This summary should not be considered apart from the entire text of this report. This report should be read and evaluated in its entirety prior to using our engineering recommendations for the preparation of design or construction documents. Details of our findings and recommendations are provided in subsequent sections of this report and in the attached figures. 1. Four (4) exploratory borings were drilled to evaluate soil conditions. The subsurface profile varies slightly among the boring locations. At borings B-1 and B-2 (southeast area of site) the subsurface profile consisted of 5 to 6 feet of dark grayish brown, light gray, light yellowish brown, medium grayish brown, and medium yellowish olive-brown highly plastic clay and gravel with some sand content (CH and GC classifications), overlying a massive stratum of light gray, light yellowish brown, and light olive-brown highly plastic clay ( Del Rio Cay ) to a depth of at least 30 feet. At boring B-3 the surface stratum (upper 6 feet) of dark brown and medium yellowish brown clay only contained trace gravel content and was underlain by the massive highly plastic Del Rio Clay. At a 4 th boring location the surface stratum (8 feet thick) of dark brownish gray and medium yellowish brown clay was only moderately plastic (CL) beyond a depth of 2 feet. Groundwater was not 1

4 encountered during the drilling operation in October The maximum depth of exploration was 30 feet. 2. The Del Rio Clay can be susceptible to significant swelling and shrinkage potential. The TxDOT PVR site index was calculated to range between 2 ½ inches to 3 ¾ inches due to the plasticity and soil profile (gradation). Potential vertical soil movement (design PVR) however was calculated to be over 7 inches at the surface if no soil improvement is performed and notable changes in moisture content occur within an active zone 15 feet deep. The design PVR under a lightly to moderately loaded foundation slab was calculated to be 5 ½ inches to 7 inches if no soil improvement is performed and notable changes in moisture content occur post-construction within a 15-ft deep active zone. 3. Based on the available soil information, proposed construction, and assumed structural loads, the project team can consider two foundation options: Option A: The approximately 9,100 square-foot building can be constructed on a structurally supported slab cast on void boxes and constructed on deep concrete belled drilled piers. Recommendations concerning the design and construction of the drilled piers are presented in this report. Recommendations concerning a driven steel pipe pile alternative to concrete drilled piers can be provided upon request. Option B: Perform significant soil improvement and construct the 3-story building on a ground-supported stiffened slab foundation system (foundation slab). The building must be designed to accommodate some differential soil movement. Various options for soil improvement and foundation slab design are presented in this report. 4. Based on a finished floor elevation assumed to be close to existing grade at the upslope side of the building, we assume 4 inches to 40 inches of fill will be required to reach planned slab subgrade elevation across the footprint before consideration of any soil improvement. Recommendations concerning earthwork and pavement thickness design are also included in this report. 5. Surface drainage should be designed, constructed, and subsequently not adversely altered by the Owner, to provide rapid removal of water runoff away from all sides of the building and away from the edges of pavement or flatwork. 2

5 SITE LOCATION AND CONDITIONS The project site is a 1.23-acre lot located on the east side of the MoPac Expressway northbound frontage road (Burnet Road) and the south side of Grand Blvd., in the north area of Austin, Travis County, Texas (Figure 1 and Figure 2). The site was wooded across the northern area and contained wild shrubs across the central and southern areas. An existing concrete driveway ramp is present in the southwest corner. The underbrush was cleared from parts of the central and south areas by the Owner to provide access to a drill rig in the non-wooded areas. The USGS topographic map shows no indication of any potentially backfilled pre-existing pond, quarry pit, or landfill at the site at the time the map was made (see graphic). An old creek valley is aligned northwest to southeast across the north end of the site. The USGS map presents the original alignment of Burnet Road, which is now under the MoPac Expressway mainlanes. The pond in the old USGS map is still present in LANDFILL LITERATURE REVIEW The City of Austin 2004 Supplemental Assessment: Landfills in the Vicinity of Austin, Texas, and the 2002 CAPCO (Capital Area Planning Council; now the Capital Area Council of Governments) Closed and Abandoned Landfill Inventory report (and the 2010 update) for Travis County were reviewed and there were no small unpermitted landfills (dumps) identified at the subject property. A City of Austin Certification of Compliance form is provided as Figure 12. 3

6 PROPOSED DEVELOPMENT AND CONSTRUCTION The proposed development includes a 3-story, approximately 9,100 square-foot, hotel building with associated parking lot paving. A site plan was provided to Capital Geotechnical Services and was used for the boring location plan (Figure 4). Information concerning structural loads was not provided to Capital Geotechnical Services. We have assumed that the building will consist of wood framing and structural loads will not exceed 75,000 lbs for any column loads and 3,000 lbs per foot for wall loads. Information concerning planned finished floor (FF) elevation and existing topographic ground surface elevation data was not provided to Capital Geotechnical Services by the time of this report. We have therefore assumed that planned finished floor elevation will be close to, but just above, existing grade on the upslope side of the building (i.e. FF elevation 8 inches above upslope grade). Based on a cursory observation of the site, there appears to be approximately 3 feet of ground surface elevation difference across the planned building footprint area. Therefore we assume 4 inches to 40 inches of fill will be required to reach planned slab subgrade elevation before consideration of soil improvement. We assume minor cut and fill grading will be required to reach planned pavement subgrade elevation and to accomplish final grades for drainage design purposes. If the proposed construction varies from what is described in this report, Capital Geotechnical Services must be contacted to determine if revisions to our recommendations are required. GEOLOGY AND SOIL MAPPING INFORMATION According to the USDA Natural Resources Conservation Service shallow soil mapping information, the shallow soils (upper 5 feet) of the project site may be a member of the Heiden Clay soil series. This soil generally classifies according to the USCS as fat clay (CH). According to the survey, the soil is commonly dark grayish brown and is commonly mapped above the Del Rio Clay formation. According to available geology mapping information by the U.T. Bureau of Economic Geology, the site is located in the Balcones Escarpment (fault zone) geologic physiographic province and consists of a clay sedimentary deposit categorized as the Del Rio Clay geologic formation. The local area is faulted and a limestone rock sedimentary deposit categorized as the Georgetown Limestone formation might be present along the west area of the site. A geology map is provided in Figure 3. 4

7 SUBSURFACE EXPLORATION Partial site mowing was performed in the non-wooded areas to remove tall underbrush. Four (4) exploratory borings were drilled to evaluate soil conditions. The borings drilled in this exploration were located in the field by Capital Geotechnical Services by measurements from existing structures and site features such as the southeast property corner, the eastern property line, and the fire hydrant at the northwest corner. The boring locations were selected to be along the east edge of the building area due to the potential presence of a fault line and limestone rock formation in the west area of the site. The presence of clay had to be determined to avoid potential significant design errors if only limestone rock was exposed in borings on the west side of the building. The borings were drilled on October 9, 2015, to a depth of 30 feet in the building area at the approximate locations indicated in Figure 4. Drilling was performed using a truck-mounted drill rig equipped with 4-inch diameter continuous flight solid stem augers, a Shelby tube sampler, and a split-spoon sampler. A hammer weighing 140 pounds falling 30 inches was used to drive the split-spoon sampler. Boreholes were backfilled with available auger cuttings. The soil samples were delivered to our laboratory where they were visually classified by a Geotechnical Engineer and selected samples were subjected to laboratory testing. Detailed boring logs are provided as Figures 5 to 8. LABORATORY TESTING Representative soil samples were selected and tested to assist the visual classifications and to determine pertinent engineering and physical characteristics. Tests were performed in general accordance with applicable ASTM standards. Results of the laboratory tests are included on the boring logs. Specialized testing to determine the presence of chemicals in soil samples (e.g., sulfates, chlorides) was not requested. A Geotechnical Engineer classified each soil sample on the basis of texture and plasticity in accordance with the Unified Soil Classification System (USCS). The USCS group symbols for each soil type are indicated in parentheses following the soil descriptions on the boring logs. Expansive properties of 4 samples of clay soil were evaluated by performing swell tests. The test consists of placing a remolded specimen in a rigid ring at the as-sampled moisture content, applying a light seating load, allowing the sample to absorb water, and measuring the vertical heave of the sample while not allowing horizontal (lateral) strain. The results of such testing are used by the Geotechnical Engineer to help properly evaluate the clay mineralogy and the shrinkswell behavior of the clay soil. 5

8 Soil samples that remain after testing will be kept for 3 weeks after the date of this report. Samples will then be discarded unless we receive instructions regarding their disposition. SUBSURFACE CONDITIONS Information from the exploratory borings indicates that the soil stratigraphy may generally consist of 4 distinguishable strata above a depth of 30 feet. The characteristics of these strata are summarized in the following paragraphs. Stratum A: Dark to Medium Clays with Variable Gravel Content The upper 5 to 6 feet of soil in the building area appears to consist of dark grayish brown, dark brown, medium yellowish brown, light gray, light yellowish brown, medium yellowish olive-brown, and medium grayish brown, highly plastic clay with trace gravel and trace sand (CH) and clayey gravel with sand (GC). The darker colored soil was generally within the upper 2 feet. The gravelly soils were encountered at B-1 and B-2. SPT N-values ranged between 13 blows per foot (bpf) and 37 bpf for the 8 tests performed exclusively in this stratum. Two samples of the finer fraction of the soils were tested to determine plasticity (Atterberg limits) and yielded a liquid limit (LL) of 59% and 61%, and a plasticity index (PI) of 40 and 41. One remolded specimen was subjected to swell testing and exhibited 26.2% vertical swell (Figure 11) from an initially hard and moderate moisture condition, indicating the soil has relatively high shrinkage and swelling potential. Stratum A2: Yellowish Brown Lean Clay At boring B-4 exclusively, a stratum of light to medium yellowish brown lean clay (CL) (moderately plastic clay) was evident from a depth of approximately 2 feet to a depth of at least 8 feet. This soil is slightly different from the shallow soils encountered in the building area but might simply be of the Del Rio Clay geologic formation that frequently includes clay minerology and gradation that produce a lean clay classification. One sample was tested to determine plasticity and yielded a LL of 44% and a PI of 29. Stratum B: Del Rio Clay Beyond a depth of 5 to 6 feet in the building area the soils consisted of light gray, light yellowish brown, and light olive-brown highly plastic clay (CH) to a depth of at least 30 feet. The soil included trace white gypsum, trace black mottling, some varved structure with medium gray lenses, and trace orange-brown color. The clay was very stiff to hard, exhibiting SPT N-values ranging between 23 bpf to 79 bpf for the 16 tests performed in this stratum. Five samples were tested to determine plasticity and yielded a LL of 57%, 58%, 64%, 65%, and 66%, and a PI of 37, 39, 40, 43, and 45. Three remolded specimens were subjected to swell testing and exhibited 28.5%, 28.6%, and 32.9% vertical swell from an initially hard condition and moderate moisture condition, indicating the soil is susceptible to significant shrinkage and swelling movement. 6

9 Stratum D: Hard Pale Silty Clay At boring B-1 exclusively, a stratum of dry to moist, very hard, pale grayish brown lean clay (CL) was encountered starting at a depth of approximately 22 feet and extended to a depth of at least 30 feet. Some fine sand content was present in the deeper sample. SPT results were 50/5 and 50/4, indicating the soil was very hard. One sample was tested to determine plasticity and yielded a LL of 34% and a PI of 19. The above descriptions are of a generalized nature to highlight the major soil stratification features and soil characteristics. The boring logs provided in the Appendix should be reviewed for specific information at each location. The stratification of the soil represents our interpretation of the subsurface conditions at the boring locations based on observations of the soil samples by a Geotechnical Engineer. Variations from the conditions shown on the boring logs could occur in areas in between borings or in areas around the borings. The stratification lines shown in the boring logs represent approximate boundaries between soil types and condition, and the transitions may be gradual rather than distinct. It is sometimes difficult to identify changes in stratification within narrow limits. It may also be difficult to distinguish between fill and discolored natural soil deposits if foreign substances are not present. Groundwater was not encountered in our exploratory borings at the time of drilling. Moisture contents were relatively low, indicating that groundwater was not present. Groundwater, however, can be temporary instead of perennial. Although groundwater was not encountered during the drilling and sampling operation, our experience requires us to emphasize that groundwater can still appear later (e.g. during construction of drilled shafts). The Owner, General Contractor, and drilling subcontractor should not be surprised if groundwater appears and requires temporary mitigation measures. Groundwater may develop after periods of rain and can develop after construction in response to landscaping irrigation or changes to nearby drainage conditions. Perched groundwater will most likely appear within fissures in the clayey soils. POTENTIAL MOVEMENT OF THE CLAY SOILS The clay soils within the zone of seasonal moisture change (or within a potential active zone) will experience changes in condition due to changes in environmental conditions (rainfall quantities and frequency; temperature; evaporation; tree roots) and man-made conditions (leaking water lines; irrigation; poor drainage) that affect the moisture content of the clay soils. The clay soil may harden, shrink, and crack when subjected to drying, swell when subjected to wetting, and soften when subjected to saturation. The TxDOT Potential Vertical Rise (PVR) index (Tex-124-E) considering existing conditions and existing overburden pressure was calculated to be between 2 ½ inches and 3 ¾ inches based on the plasticity of the soil and the soil profile (gradation). It was assumed that the clay would be 7

10 in an initially dry condition as defined by the method at the time of construction and that the thickness of the active zone is 15 feet. Note that the TxDOT PVR method assumes limited wetting occurs and should only be used as an index tool for comparing sites. The TxDOT PVR value should not be considered an estimate of maximum potential vertical heave. Using reasonable estimates of relatively dry and relatively moist suction profiles or moisture content profiles and physical properties of the clay soil, the swelling potential of the clay soils within the active zone (assumed to be 15 feet deep) may be 7 inches or more at the surface under new flatwork if the moisture content changes between a relatively dry condition and a relatively moist condition near the surface, tapering to negligible change at a depth of 15 feet. The design PVR does not consider extreme moisture change conditions (i.e. 200-year to 500-year drought, rainfall, or groundwater event, etc.) but does consider significant potential changes due to manmade and environmental conditions. Under a light to moderate foundation slab load, a design PVR of 5 ¾ inches to 7 inches was calculated considering the same potential changes in moisture content within the active zone. The potential amount of total and differential heave or shrinkage is difficult to accurately predict because it will depend on the extent of impervious cover, seasonal changes in climate conditions, drainage conditions, presence of leaking water pipes, groundwater conditions, landscape watering, vegetation planting, thickness of clay soil affected, and varying physical characteristics and mineralogy of the clay soils. The PVR is not a static value because it depends on how the soil behavior and the boundary conditions are modeled such as what changes in moisture content to consider and what initial moisture condition to consider at the time of construction. Deep-seated swell movements can also occur if swelling of the deeper clay soils is caused by water sources other than those that affect moisture content variations near the surface (notable groundwater development; leaking nearby water main; leaking deep sewer pipe; etc). SITE PREPARATION AND EARTHWORK The primary geotechnical concern that will influence foundation or slab performance at this site is the presence of expansive clay soils. We believe that the impact of swelling and shrinking soils can be mitigated with proper planning, engineering design, and construction quality control as discussed in this report. Soil Improvement in the Building Area The potential soil movement due to shrinkage and swelling can be reduced by using soil improvement techniques to change the characteristics and properties of the subgrade soils. Options for soil improvement include: 8

11 Option 1: Removal of a certain thickness of existing clay soil and replacement with properly compacted select fill (structural fill). Option 2: Pre-swelling and modification of clay soil by water and chemical pressure injection (i.e. electro chemical injection, acid treatment injection, or ionic stabilizer injection ; or potassium chloride injection). A deep perimeter moisture-evaporation barrier might be required depending on the results of the quality control testing of the injection operation. A cap of properly compacted select fill will also be required to provide durably stiff subgrade support immediately under the foundation slab. Option 1: Removal and Replacement The thickness of removal and replacement will be selected by the Owner, Architect, and the Structural Engineer since multiple factors affect how much vertical movement can be tolerated by the structure (type of cosmetics used, flexibility of framing detailing and cosmetics, aversion to risk, tolerance to cosmetic cracking and functional distress, stiffness of framing to resist wind loads, rigidity of slab, design deflection tolerance, etc). Design parameters for various thickness of soil improvement are provided in this report. Select fill should extend at least 5 feet beyond the perimeter of the building. Select fill extending beyond the building footprint should be capped in landscaped areas with an 18-inch thick clay soil to limit infiltration of surface water into the pad fill. Option 2: Water and Chemical Pressure Injection Water and chemical pressure injection is performed by a specialty subcontractor. The purpose of the water and chemical pressure injection is to pre-swell the existing clay soil and modify the soil characteristics. The depth of treatment should be 12 feet and the treatment should extend horizontally at least 5 feet beyond the perimeter of the slab footprint area. The equipment is typically similar to a tracked dozer equipped with a custom injection rod frame and system. Injection treatment will require a follow-up investigation to determine if the method produced the desired pre-swelling and modifications to the physical properties of the clay soil. The quality or extent of the modification will partially depend on the extent of cracking and fissures within the clay strata. The low permeability of the clay soil and the potential lack of sufficient cracks will cause the method to not produce a homogeneous modification of the clay soil. Quality control (QC) testing is necessary to achieve good quality results. 9

12 Completion of the pre-swelling aspect of the injection improvement operation is achieved when the desired moisture condition is reached. We do not propose any method-based specifications, only end-result based specifications. After performance of the injection procedure, drilling and sampling will be required to obtain soil samples. The target moisture condition can be associated with stiffness and swell potential. Moisture content, pocket penetrometer, and swell tests will have to be performed to measure the success of the pre-swelling injection operation. Pocket penetrometer test results should be between 1.0 tsf and 3.5 tsf after a successful injection operation. The vertical swell of a post-injection sample should not exceed 2% if a remolded specimen or 1% if an undisturbed sample. Atterberg limits tests and shrink-swell tests will have to be performed to determine if the chemical compounds changed the physical properties of the clay soil. Capital Geotechnical Services should be retained to inspect the injection operation to document means and methods, and the follow-up QC testing should be performed by Capital Geotechnical Services. The recommended design PVR after a successful injection operation is 1 ½ inches unless the chemical modification aspect is suspected of yielded poor results. If the quality of the chemical modification is suspect, deep vertical moisture-evaporation barriers must be installed. Note that water and chemical pressure injection will produce a soft subgrade. The construction schedule must allow for at least 2 weeks of curing time in the cool season (when no rainfall is forecast) or 1 week during the summer season after completion of the injection operation to permit the shallow treated clay soils to dry out and stiffen to support construction traffic and to permit the proper installation of the first lift of new fill. Stripping and Clearing All of the grass topsoil (soil with high organic content), tree roots and root bulbs, vegetation, and deleterious forest materials (downwood, litter, duff) must be removed from the proposed building and pavement areas at the start of construction. The stripped organic materials and organic-rich soils must be stockpiled separate from excavated soil that will be re-used as minor grading fill. Stripping should be observed and documented to record that unsuitable materials were removed prior to placement of fill, slab, or pavement materials. Backfilling of Buried Utilities Water and sewer lines are typically constructed beneath paved parking lots. Compaction of trench backfill or lack thereof can have a significant effect on the performance of the pavement. Trench backfill should be placed in lifts not exceeding six (6) inches in loose lift thickness if using lightweight compaction equipment (walk-behind or remote controlled rollers, mechanical tampers, vibratory plate compactors, boom-mounted trench rollers), and eight (8) inches if using heavy 10

13 trench rollers. Onsite clay soil backfill should be moisture conditioned to between +2% and +5% above optimum. All other backfill soils should be moisture conditioned to between -1 and +3 percentage points of optimum, and compacted to achieve a relative compaction of 95% or higher based on the Standard Proctor method (ASTM D 698). The placement and compaction of the backfill should be observed, tested, and documented by a Capital Geotechnical Materials Technician. Utility trenches within clay soils, backfilled with clean sand or gravel can function as postconstruction conduits for water below the building or pavement. This can result in swelling of clay soils affected by the water along the trench and result in development of cracking and heaving in the pavement or building and slab along the trench alignment. Capital Geotechnical Services recommends using fine-grained backfill such as on-site trench cuttings or imported low to medium plasticity clay (CL) or clayey sand (SC) to backfill utility trenches. The backfill must not be densely compacted under the building slab (i.e. allow some soil compressibility within the trench). An alternative is to surround the trench with a geosynthetic geomembrane between the backfill and the surrounding clay soil and design the trench system to drain water to an acceptable outfall area or stormwater sewer system. Alternatively, concrete cut-off collars or clay plugs should be included in the trench design to prevent water from entering sections of trench beneath slab and pavement areas. Utility trenches within clay soils under a structurally supported slab and backfilled with clean sand or gravel can result in development of heaving of pipes and fixtures near the trench as the clay under the trench swells. Although sleeves through the slab can permit movement, the fixtures connected to the pipes cannot tolerate notable movement. Recommendations for plumbing installation when using a slab cast on void boxes are provided later in this report. Fill Placement Select fill that is imported to the site for use under a foundation slab or pavement should be classified according to the Unified Soil Classification System (USCS) as SM-SC, SC, GM-GC, or GC, and should meet the following criteria: Percent passing the #4 sieve: 50% to 80% (20% to 50% gravel) Percent passing the #200 sieve: 20% to 45% PI of soil passing the #40 sieve: 6 to 19 Maximum size of gravel or rock fragments: 3 inches in any dimension 11

14 If a soil improvement excavation is performed, the project team should consider extending the excavation and subsequent fill pad horizontally more than 5 feet from the edge of the building where deemed necessary to include flatwork. Note that joint faulting or crack faulting can impact ADA compliance associated with tripping hazards. Select fill should be placed in horizontal loose lifts of not more than 6 to 8 inches in thickness depending on the size and weight of the compaction equipment. Select fill should be moisture treated and compacted to achieve a minimum relative compaction of 98% based on the maximum dry unit weight as determined by the Standard Proctor method (ASTM D 698). Moisture content of select fill material should be within -1 and +3 percentage points of the optimum moisture content at the time of compaction (-1% to +3%). Some wetting or drying might be required to produce the necessary moisture content at the time of compaction. The performance of slabs and pavement placed on new fill material is influenced by the quality of the compaction and materials selection of the fill material. Capital Geotechnical Services should be retained to perform quality control testing and inspection during selection, placement, and compaction of the fill material. Appropriate laboratory tests such as Proctor moisture-density tests should be performed on samples of fill material and pavement base course material. Field moisture-density tests and visual observation of lift thickness and material types should be performed during compaction operations to verify that the construction satisfies material and compaction requirements. In-place moisture-density tests and lift thickness checks must be performed on every lift of fill. Fill materials should not be placed on soils that have been recently subjected to precipitation or saturation. All wet soils should be removed, or reworked, or stabilized, or allowed to dry prior to continuation of fill placement operations. Fill soils must be free of wood debris (organics) such as large branches, thick roots, and wood chips since over time these organic materials will decay, causing localized settlement or creating voids. Water entering voids can eventually lead to collapse of the void and settlement under pavement or under a slab. Boulders and cobbles must be removed from the fill mass during placement. Soil around the edges of such stones cannot be properly compacted, and unfilled voids might be created due to bridging of soil over adjacent boulders or cobbles. Loose soil can compress when wetted, and soil above voids can migrate into the void space, causing settlement. If any problems are encountered during the earthwork operations, or if newly exposed soil and site conditions are different from those encountered during our subsurface exploration, the 12

15 Geotechnical Engineer must be notified immediately to determine the effect on recommendations expressed in this report. If construction is performed during winter or spring seasons when the occurrence of rainfall is more frequent, to limit effects of wet weather, the building pad or pavement area can be initially graded high or left crowned to protect the slab or pavement subgrade. The additional soil can be removed when slab or pavement construction can begin. Certain construction practices can reduce the magnitude of problems associated with moisture content increases of subgrade soil for pavement, slabs, and areas to receive compacted fill. If rainfall appears imminent, the contractor should seal exposed subgrade areas at the end of the work day with a smooth drum roller to reduce the potential for infiltration of water into the subgrade. Pavement base course should preferably consist of well graded aggregate and not open graded aggregate, but should conform to any locally developed guidelines. Site grading should be continuously evaluated to assure that surface runoff will drain away from pavement, slab, and fill areas. In pavement areas, final grading of the subgrade must be carefully controlled so that low spots in the subgrade that could trap water in the base course (asphalt pavement) or under a concrete joint are eliminated. FOUNDATIONS Based on the subsurface conditions encountered and our experience with similar construction, the project team can consider two foundation options: Option A: The approximately 9,100 square-foot building can be constructed on a structurally supported slab cast on void boxes and constructed on deep concrete belled drilled piers. An alternative to concrete belled piers is to use driven steel pipe piles. Option B: Perform significant soil improvement and construct the 3-story building on a ground-supported stiffened slab foundation system (foundation slab). The building must be designed to accommodate some differential soil movement. Various options for soil improvement and foundation slab design are presented in this report. Recommendations concerning the design and construction of the foundations are presented in the following paragraphs. The Owner, in consultation with the design team, should decide on the level of performance desired and the relative economics of constructing either a shallow or deep foundation system. 13

16 Drilled Pier Option: 1. Based on the assumed maximum structural loads and on the soil conditions encountered, the 3-story wood-framed building can be supported by belled concrete drilled piers. Piers should have a shaft diameter of 12 inches or larger and must be adequately belled and penetrate deep enough to provide significant uplift force resistance against swelling clay soil in contact with the pier. 2. Piers can be designed to apply a maximum allowable bearing pressure of 12,000 psf if ¾ to 1 inch of settlement is deemed acceptable, subject to approval of bearing conditions at the time of construction. We assume a lower bearing pressure will be required for the 3- story wood framed structure, therefore the anticipated settlement will be less than ¾ inch. Skin friction should not be considered when using moderate depth belled piers. The structural design of the piers, including the amount and type of reinforcing steel and the strength and mix design of the concrete will be determined by the project Structural Engineer. The project team can refer to ACI for recommendations concerning writing specifications for drilled pier construction. 3. Since belling in hard clay is difficult, if there is any uncertainty about the capability of the belling tool and drilling equipment to open the belling tool fully, or if there is any uncertainty about the drilling subcontractor performing an adequate number of belling tool runs to form a complete bell (i.e. time consuming), then the design capacity should consider a reduced bell diameter for design purposes (i.e. use a 30-inch diameter bell if a 36-inch diameter is specified, or a 45-inch diameter if a 54-inch belling tool is specified). If piers can be constructed with a heavy truck-mounted drill, then a full bell diameter can be achieved in the field with notable effort (multiple belling tool runs; may add water). 4. The center-to-center spacing should be 3 bell diameters or larger. Closer spacing will require reductions in uplift capacity and end bearing capacity due to the combined influence on a zone of bearing material by more than one pier. If piers are closer than 3 diameters center-to-center, then the capacity should be reduced to a fraction of the recommended values for a stand-alone pier. The reduction factor will vary from 0.50 (piers edge-to- edge) to 1.0 (piers at two diameter edge-to-edge spacing). Interpolation can be used for pier spacing between zero and two diameters edge-to-edge. 5. The potential uplift force anticipated from swelling of the clay soils in the zone of seasonal moisture change or a reasonable potential active zone can be approximated as 105 D kips if the clay soils are in a relatively dry condition at the time of construction, where D is the 14

17 diameter of the pier in feet. The depth of the active zone is assumed to be 15 feet. Note that no factor has been applied to potential uplift force (i.e. no load factor or LFRD design). Piers should be sufficiently reinforced to resist tensile stresses associated with swelling of the surrounding clay. 6. The diameter of the bell should be three times the diameter of the straight shaft to resist uplift forces associated with the swelling of the upper soils and to reduce the risk of caving during construction of the bells. Uplift resistance is calculated from empirical models and the contribution to uplift resistance is likely influenced by the weight of the soil above the bell, the shear strength of the soil above the bell, the dead weight of the pier, and downward structural axial load (dead load DL ). Belled piers will provide uplift resistance against swelling clay and against wind shear loads and the uplift capacity can be estimated to be: 12 shaft / 36 bell, embedded 21 feet below grade: 78 kips + DL applied at top of pier 12 shaft / 30 as-built bell, embedded 21 feet: 65 kips+ DL applied at top of pier 12 shaft / 36 bell, embedded 22 feet below grade: 94 kips + DL applied at top of pier 12 shaft / 30 as-built bell, embedded 22 feet: 72 kips+ DL applied at top of pier 12 shaft / 36 bell, embedded 23 feet: 105 kips+ DL applied at top of pier 12 shaft / 30 as-built bell, embedded 23 feet: 75 kips+ DL applied at top of pier 18 shaft / 54 bell, embedded 21 feet below grade: 106 kips + DL applied at top of pier 18 shaft / 54 bell, embedded 22 feet below grade: 129 kips + DL applied at top of pier 18 shaft / 45 bell, embedded 22 feet below grade: 109 kips + DL applied at top of pier 18 shaft / 54 bell, embedded 23 feet below grade: 153 kips + DL applied at top of pier 18 shaft / 45 bell, embedded 23 feet below grade: 128 kips + DL applied at top of pier Note that no factor of safety has been applied to uplift resistance values (i.e. ASD design), therefore a deeper penetration can be considered. 7. A minimum void of 10 inches should exist beneath the grade level beams between piers to accommodate future swelling of the clay subgrade soil and prevent the application of uplift forces on the grade beams and on the piers. The void concentrates the dead loads onto the piers. The voids can be created using cardboard forms (void boxes). The soils below the grade beams should be graded to drain away from the piers (grade beam trench and void space down to middle of trench between piers). 8. A dry method of construction may be adequate to construct open shafts. In the event of rain or water seepage into the shaft, no more than 5 inches of water should be present at 15

18 the bottom of the shaft when concrete placement begins because of the risk of washing out cement in the bottom portion of the pier. Loose soil or debris should not be present at the bottom of the shaft when concrete placement begins. Poor cleaning of compressible cuttings at the bottom can lead to significant settlement. 9. Concrete should be placed the same day the shaft drilling is completed to limit changes in the shaft bottom and shaft sidewalls that can reduce mobilized capacity and to reduce the risk of bell cave-in. 10. To reduce the potential for arching within the shaft or casing, Capital Geotechnical recommends using a concrete mix with a slump of 5 inches to 7 inches. If the concrete has a slump that is less than or equal to 7 inches, the upper 5 feet of concrete should be vibrated to assure proper consolidation in that region. If the slump is greater than 7 inches, the concrete should not be vibrated because of the potential to segregate cement and aggregates. 11. Mushroom tops must not be produced or left in place after the concrete placement. Heaving of clay soil against protruding concrete (enlarged pier top) can produce notable uplift force that is not considered in the design of the piers. 12. A tremie pipe can be used to place concrete to prevent segregation of concrete ingredients and to prevent moving the reinforcing steel cage. A free-fall method might allow the concrete to strike reinforcing steel, casing, or shaft sidewalls, causing segregation and undesirable concrete strength properties. A free-fall method is acceptable if the concrete is directed through a hopper and falls down the center of the shaft without striking the sides of the shaft or the reinforcing steel cage. 13. The contractor can refer to ACI for ACI recommendations concerning concrete pier construction. 14. The performance of the foundation system is highly dependent on the quality of the installation. Therefore, Capital Geotechnical Services should be retained to document the drilling conditions encountered, the cleaning of the bottom of the shaft, the type of bearing material, the depth and diameter of pier, and the size, number, configuration, and grade of steel reinforcement. 15. Concrete material should be sampled and tested for compressive strength, and placement operations should be monitored to record concrete slump, temperature, and age at time of placement. Detailed concrete batch tickets should be provided by the supplier to permit review and documentation of water-cement ratios and cement content. 16

19 16. Horizontal forces (lateral loads) can be resisted by a combination of the soils around the piers and the stiffness of the piers. Capital Geotechnical Services can assist the Structural Engineer with lateral load analysis by providing the soil-related design parameter values if the method of analysis is indicated to us. 17. A sulfate resistant concrete mix should be used due to historically high sulfate concentrations in the Del Rio clay and clay-shale. We recognize that Type 5 cement may not be readily available. Concrete made with cement that meets ASTM C 150 Type 2 requirements, 25 percent Class F fly ash, and a maximum water-cementitious material ratio of 0.40 can be used to provide notable resistance. The fly-ash should meet ASTM C 618 Class F requirements. 18. Belled piers may be difficult to install if infiltrating groundwater is encountered that can collapse the bell. The installation of the first belled piers must be carefully observed and if notable groundwater seepage is encountered, each shaft must be continuously dewatered (pumped) while waiting for the concrete to be placed (i.e. do not allow groundwater to build up inside shaft notably above lip at base of bell). This may cause a slowdown in production as concrete delivery may need to be scattered throughout the day. 19. In expansive clay soils, variations in wetting and drying with depth on opposite sides of a pier will induce changes in bending moments and shear forces in the pier. This condition should be considered when analyzing the design of a slender pier. Stiffened Slab Option: 1. The building structure can be supported on a rigid, monolithically-cast, grid-type grade beam and slab foundation system (foundation slab) if significant soil improvement is performed. When placed on expansive soils, subgrade improvement must be performed to reduce potential soil and foundation movement to levels acceptable to the Owner, Architect, Structural Engineer, and General Contractor. 2. The rigidity of a stiffened slab will limit the effects of differential soil movement caused by swelling and shrinkage of clay soils and compression of soils due to structural loads. However, discernible cracking in brittle construction materials may still occur. This type of slab should be designed with perimeter grade beams and interior stiffening grade beams adequate to provide sufficient rigidity to the slab element. The foundation slab can be designed considering an allowable bearing pressure of 2,500 psf across the grade beam contact area if all grade beams are placed on properly compacted select fill. 17

20 3. Perimeter grade beams should extend at least 18 inches below final adjacent exterior grade and have a minimum width of 10 inches. The grade beam width and depth will be determined and detailed by the project Structural Engineer. The grade beam details must specify minimum beam height and minimum beam penetration below exterior grade (ground surface). 4. Floor coverings (carpet, tile, wood, laminate, vinyl) can be damaged or subject to mold growth by moisture penetrating the slab, therefore a moisture vapor barrier (i.e. 10 mil thick geosynthetic geomembrane) should be placed on top of the select fill and properly sealed to limit the migration of moisture to and through the slab, and to serve as a separator between the fill (potentially high friction) and concrete slab. The moisture barrier can be placed after the grade beams are formed. We recommend lapping the sheets of vapor barrier 12 inches and taping the joints/laps. Since many field crews do not force membranes down to make continuous contact with the trench walls and bottom to maintain proper rectangular beam cross section, if a single sheet of geomembrane is placed across a trench, we recommend cutting the membrane at the bottom of the grade beam trench to prevent the poured cross section area from being reduced (prevent bridging at bottom corners), and installing a separate strip of vapor barrier along the bottom to overlap the cut membrane on either side of the trench. 5. The foundation slab can be post-tensioned or conventionally reinforced. The foundation slab should be designed using the PTI, WRI, or BRAB soil-related design parameter values provided in the subsequent paragraphs. 6. Guidelines for the design of a conventionally reinforced foundation slab are provided by resources such as the Wire Reinforcement Institute (WRI), the International Building Code (IBC), the International Residential Code (IRC), the 1968 FHA BRAB report, and ACI 360R. 7. We recommend the parameter values in Table 1 when designing a conventionally reinforced stiffened slab using traditional BRAB or WRI guidelines. We do not recommend designing and constructing a foundation slab on soil conditions with a design PVR greater than 1 ½ inches. Parameter values for a design PVR greater than 1 ½ inches are provided for illustration purposes only or at the exclusive risk of the Owner. The building structure must be designed to accommodate the potential vertical soil and slab movement (i.e. a stiff slab does not prevent heave; increased slab stiffness attempts to limit the effects on deflection to tolerable levels). The acceptable design deflection value will be determined by the Structural Engineer. 18

21 Table 1: Soil Improvement Condition Undercut 4 feet and replace with compacted select fill * Undercut 5 feet and replace with compacted select fill * Undercut 6 feet and replace with compacted select fill * Undercut 7 feet and replace with compacted select fill * Undercut 8 feet and replace with compacted select fill * Undercut 9 feet and replace with compacted select fill * Water and chemical inject to 12 feet and install a minimum 3-ft thick cap of compacted select fill ** Design PVR Design PI BRAB Support Index C 1-C WRI Cantilever Length 4 inches ¼ feet 3 inches feet 2 ¼ inches ¾ feet 1 ¾ inches ¾ feet 1 ¼ inches ½ feet 1 inch feet 1 ½ inches feet *: Under-cut is from existing grade. Clay must be replaced with properly compacted select fill. **: If quality control test results are deemed inadequate, an 8-ft deep vertical moisture-evaporation barrier must be installed around the building to protect the pre-swelled and treated clay soils. lc For foundation slabs designed using the BRAB or WRI type methods, long term deflection of flexural beams resulting from creep and shrinkage of concrete under sustained loading can be determined using ACI , as recommended in the Texas Section ASCE 2007 Recommended Practice for the Design of Residential Foundations. 8. Guidelines for the design of post-tensioned slab-on-grade can be found in the PTI manual Design of Post-tensioned Slabs-on-ground (2 nd Edition 1996 or 3 rd Edition 2004) and the PTI manual Standard Requirements for Design and Analysis of Shallow Post-Tensioned Concrete Foundations on Expansive Soils (2012). We recommend the soil-related parameter values in Table 2 if using a PTI method of design. We do not recommend designing and constructing a foundation slab on soil conditions with a design PVR greater than 1 ½ inches. Parameter values for a design PVR greater than 1 ½ inches are provided for illustration purposes only. The building structure must be designed to accommodate the potential vertical soil and slab movement (i.e. a stiff slab does not prevent heave; increased slab stiffness attempts to limit the effects on deflection to tolerable levels). The acceptable design deflection value will be determined by the Structural Engineer. 19

22 Soil Improvement Condition Undercut 4 feet and replace with compacted select fill * Undercut 5 feet and replace with compacted select fill * Undercut 6 feet and replace with compacted select fill * Undercut 7 feet and replace with compacted select fill * Undercut 8 feet and replace with compacted select fill * Undercut 9 feet and replace with compacted select fill * Water and chemical inject to 12 feet and install a minimum 3-ft thick cap of compacted select fill ** Design PVR Table 2 PTI Differential Movement (ym) Center Lift Edge Lift Edge Moisture Variation Distance (em) Center Lift Edge Lift 4 inches 2 ¾ inches 4 inches 5 feet 3 feet 3 inches 2 inches 3 inches 5 feet 3 feet 2 ¼ inches 1 ½ inches 2 ¼ inches 5 feet 3 feet 1 ¾ inches 1 ¼ inches 1 ¾ inches 5 feet 3 feet 1 ¼ inches 1 inch 1 ¼ inches 5 feet 3 feet 1 inch 1 inch 1 inch 5 feet 3 feet 1 ½ inches 1 ½ inches 1 inch 5 feet 3 feet *: Under-cut is from existing grade. Undercut clay must be replaced with properly compacted select fill. **: If quality control test results are deemed inadequate, an 8-ft deep vertical moisture-evaporation barrier must be installed around the building to protect the pre-swelled and treated clay soils. The vertical modulus of elasticity (E s) of immediate subgrade under slab for use in determination of the PTI beta parameter value can be selected to be 125 tsf (1,736 psi). The PTI partition load slab stress coefficient (C p) (3 rd Edition PTI manual) can be selected to be 1.10 for k s = 180 pci (compacted select fill). 9. Although the ground-supported foundation slab can be designed for vertical soil movement greater than 1 inch, the cosmetic elements of the building might not be able to tolerate the associated slab deflection. The building occupants might perceive excessive movement when they see cracking in brittle elements such as drywall, hard tile, and exterior brittle veneer (brick, stucco, stone masonry). The acceptable design slab deflection must therefore be carefully selected. The foundation slab can be designed for a PVR greater than 1 inch if an acceptable slab deflection can be achieved by the design. Potential tilting and angular distortion, however, cannot be avoided, and the effects are uncertain. The Owner must compare the risks of tilting and associated consequences, with the costs of more robust soil improvement associated with a lower risk of tilt and angular distortion. 20

23 10. Joints (for contraction and expansion crack control) should be designed and placed in various portions of the structure (i.e. drywall control joints for long wall spans, above doorways, in stairway walls, along long ceiling spans, etc). Properly planned placement of these joints will assist in controlling the degree and location of material cracking that normally occurs due to soil movements, initial wood shrinkage, expansion and shrinkage of residential construction materials from changes in humidity and temperature, and strain in framing from slab tilting, storm wind loads, and storm or man-made vibrations. 11. If the slab will be post-tensioned, the project team may consider requiring that the general contractor use a subcontractor installer who is PTI certified to help ensure the quality of the construction. 12. Exposure to the environment may weaken the soils at the grade beam bearing level if the foundation excavations remain open for an extended duration. Foundation slab concrete should be placed within 2 weeks of the completion of trench excavations and the moisture barrier should be installed before any notable rainfall event. If the bearing soils are softened by surface water intrusion or disturbance, the softened soils must be removed from the foundation excavation bottom prior to concrete placement. 13. Grade beam dimensions and reinforcing steel should be observed and documented asbuilt ( pre-pour inspection by the Structural Engineer; or by the Geotechnical Engineer if needed). 14. Prior to installation of reinforcing steel (or tendons) and the moisture-vapor barrier, Capital Geotechnical Services should be retained to observe and test the grade beam subgrade to determine if the foundations are being placed on suitable materials and to document that loose material has been removed. Dynamic Cone Penetrometer (DCP) tests can be performed to help evaluate subgrade condition. In areas where the subgrade is soft or loose, the soil should be removed and foundations lowered to bear on firm soil or foundation subgrade elevations can be restored using flowable fill approved by the Structural Engineer. 15. Concrete material should be sampled and tested for compressive strength, and placement operations should be monitored to record concrete slump, temperature, and age at time of placement. Concrete batch tickets should be provided by the supplier and collected by the General Contractor to permit inspection and documentation of water-cement ratio, cement content, and other mix design ingredients. 21

24 16. We recommend that a floor flatness survey be performed within 2 weeks after the concrete is poured to document the initial elevation profile condition of the slab. Such information will be useful if future soil and slab movement is suspected and must be compared with the initial elevation differences. Driven Steel Pipe Piles: Driven steel pipe piles can be considered in lieu of belled concrete piers to support a structurally supported concrete slab cast on void boxes. Pipe piles are typically 8-inch outside diameter elements installed to a depth great enough to provide adequate uplift resistance against swelling clay soil in contact with the pile. Capital Geotechnical Services can provide an addendum to this report upon request addressing the design of steel pipe piles if piles will be seriously considered. STRUCTURALLY SUPPORTED SLAB (IF USED) A minimum 10-inch void should be included beneath the uniform thickness portions of the slab to prevent swelling clay from inducing uplift pressures on the slab and associated piers. A void space should also be included beneath the grade beams, but a low permeability backfill (clay soil) must be used along the perimeter of the building in unpaved areas to limit water infiltration and accumulation in these voids. If carton forms are used, installation must be performed with care to assure that the void boxes are not allowed to become wet or crushed before and during concrete placement and finishing operations. Cardboard forms that have been damaged by rain must be replaced or allowed to dry and have their capacity verified before placement of concrete. Masonite boards can be applied on top of the carton forms to reduce the risk of crushing. Regional carton form suppliers include: Surevoid: Savway: VoidForm Products, Inc.: Soil retainer strips (i.e. Motzblock Sureretainer ) can be used to prevent subsequent soil backfill from displacing the void box. 22

25 To prevent potential tripping hazards, access and entry slabs by doors should be designed with care since the exterior flatwork might heave with the clay soils. The access and entry slabs can be structurally supported on drilled piers if the project team does not want any risk of joint faulting between the doorways and the exterior slabs. Doweling can alternatively be considered to prevent joint faulting but are prone to cracking the flatwork if differential movement occurs. A hinged toe-beam detail (over void space) can be used as a transition slab between a piersupported structural slab and any adjacent concrete flatwork. Capital Geotechnical Services should be retained to review construction plans and specifications to review details if a toe-beam transition element is used. Based on previous experience, we recommend that roof gutter drain downspouts not be allowed to discharge near void boxes or within nearby perimeter backfill. As part of the final punch-list inspection for the project, we recommend including an inspection to verify that roof drains were properly constructed. Due to the eventual degradation of the void boxes, a bonding moisture barrier composite with notable peel adhesion properties should be used (i.e. Barrier-Bac VBC mil) as the moisture barrier in lieu of typical smooth thin geomembrane products. SEISMIC DESIGN The subject site is located in a region of low seismicity. The region has relatively low spectral response acceleration and can be assigned to Seismic Design Category A according to ASCE 7-05 and Section 1613 of the 2012 IBC guidelines. The subject site can be categorized as a Class D site for determination of design soil shear wave velocities. PAVEMENT THICKNESS DESIGN Estimates of traffic loads and volumes were not provided to Capital Geotechnical. Capital Geotechnical has therefore assumed a daily traffic volume of 319 vehicle trips per day. This value was estimated using the ITE (Institute of Transportation Engineers) average trip generation rate of 4.90 vehicle trips per day per room for an all suites hotel land use. We understand there will be approximately 65 units in the hotel. Information on planned pavement surface grades was not provided to Capital Geotechnical Services at the time of this report. We assume minor fill or excavation may be required to reach planned pavement subgrade elevation across the site. Excavated clay can be re-used as fill 23

26 material for the pavement areas since subsequent soil improvement is expected. Options for pavement thickness design are presented below. Option A: Concrete Pavement w/ Lime Stabilization 6.0 inches jointed reinforced concrete pavement (JRCP) 4.0 inches crushed limestone base material 6.0 inches lime stabilized clay subgrade Water and chemically treated clay to a depth of 6 feet below planned pavement surface Concrete pavement should be at least 7.0 inches thick at the ramp to Grand Avenue. Concrete pavement thickness can be reduced to 5.0 inches along strips of parking lot spaces where there is no potential for heavy vehicles (i.e. delivery trucks; charter busses) to park temporarily. Option B: Asphaltic Pavement w/ Lime Stabilization 2.0 inches hot-mix asphalt (HMA) Type D 8.0 inches crushed stone flexible base Grade 1 Type A 6.0 inches lime stabilized clay subgrade Water and chemically treated clay to a depth of 6 feet below planned pavement surface Option C: Asphaltic Pavement w/ Geogrid 2.0 inches hot-mix asphalt (HMA) Type D 10.0 inches crushed stone flexible base Grade 1 Type A Geosynthetic Geogrid Tensar TX5 Water and chemically treated clay to a depth of 6 feet below planned pavement surface The designs are based on the following parameters or assumptions: - Average daily traffic (ADT): 319, with 50% lane distribution, with 0% annual growth, and 2.82% trucks of all sizes (9 trucks per day) (small, medium, and large trucks) kip ESALs (based on an average equivalency factor of 0.65 for trucks and busses, and for cars, SUVs, and pickup trucks) 43,179 over a 20 year period. - HMA Structural Coefficient: Flexible base Structural Coefficient: Lime stabilized clay Structural Coefficient: AASHTO Terminal Serviceability Index value: Analysis Period: 20 years (20 years to first significant rehabilitation). - Design resilient modulus of subgrade soil: 4,500 psi (untreated CH soil) 24

27 If the assumptions concerning traffic volume and loads are not reasonably correct, Capital Geotechnical should be notified so that we can revise our recommendations if necessary. Geometric pavement design should conform to any locally developed guidelines. Pavement thickness sections are developed using methods that consider the structural capacity of the pavement section. Although they account for some loss of serviceability due to swelling of expansive clays, they do not consider or model the cracking that develops that is damaging to the aesthetics of the pavement and they do not adequately model the loss of serviceability (bumps) that develops from cracks and differential vertical movements under the pavement. Lime stabilizing the upper layer of the clay or placing geogrid alone will not stop cracking and in fact will still allow significant amounts of cracks to form if the clay soils have sufficient swelling potential at the time of construction (hard and dry clay). We have therefore included a soil improvement option to reduce the potential soil heave under pavement by performing water and chemical pressure injection to a depth of at least 6 feet in the pavement areas. Another option for deep soil improvement includes removal of several feet of clay and replacement with properly compacted select fill with adequate fines content. It is difficult to quantify the benefits of any of the soil improvement (injection; removal and replacement) and immediate subgrade improvement (lime stabilization; geogrid) alternatives. Even with these efforts, some cracking should be expected because of the high potential for vertical movements of the underlying untreated clay soils. Pavement design is a subjective analysis that involves a tradeoff between performance and cost. The more robust and expensive the subgrade treatment and pavement section, the better the long term performance. The thinner and cheaper the pavement section and lack of attention to subgrade treatment, the more the pavement performance will be poor. Our recommended alternatives offer a balance between the two. The Owner and project team can choose options based on costs and tolerance to cracking, joint faulting, crack faulting, changes to surface runoff profile, potential tripping hazards, and other effects of constructing pavement on expansive clay soils. If curb and gutter is used, the detail must include reinforcing steel. Expansive clay soils that heave curb elements can cause severe separation cracking in curb and gutter. Reinforcing steel will limit crack widths and the associated aesthetic damage. 25

28 CONCRETE PAVEMENT COMMENTARY Concrete paving should be used in front of any dumpster pads such that the truck is supported on concrete pavement while loading and unloading the dumpster, and must be used for the ramp to Burnet Road at the north area of the site. Jointed reinforced concrete pavement (JRCP) can be considered to provide a more durable pavement system. Relative to HMA, the disadvantages of concrete paving may be its initial higher cost, susceptibility to joint faulting (affects ride quality), the larger amount of effort required to install future utility trenches (open cut), and the cost of maintenance efforts such as joint cleaning, joint sealing, and grinding. The advantages of concrete paving may include less frequent maintenance efforts, more durable ride quality, no deterioration caused by oil leaks, good light reflectivity that enhances pedestrian and vehicle safety at night and in rainstorms, and relatively good skid resistance. Concrete pavement design should conform to recognized design methods such as the ACI Manual of Concrete Practice, ACI 330R-01: Guide for Design and Construction of Concrete Parking Lots. Stabilization of fine-grained soil under concrete is recommended to provide long term stiff subgrade under concrete. Otherwise, as moisture content increases in soil under concrete occur over time, the untreated fine-grained soil will lose stiffness and lead to forced displacement of soil along edges and through cracks or joints with cycles of heavy vehicle loads (garbage trucks, beverage trucks, delivery trucks, etc..), and lead to slab deflection and cracking in those areas and possible joint faulting between panels. Joint patterns should be carefully designed to avoid irregular shapes and to provide a sufficient number of joints to control cracking associated with concrete expansion and contraction. Capital Geotechnical recommends that joint spacing not exceed 12 feet for any panel if the tolerance to shrinkage cracking will be low. Larger joint spacing can be considered by the Owner at the Owner s risk. As reported by the FHWA and SHRP, in relatively warm and dry climates like central Texas, short joint spacing is generally desired to reduce the effects of climate. The greater the joint spacing, the greater the occurrence of transverse cracking. Joint layout and detailing should be included on the site civil plans by the project Civil Engineer, or a joint plan can be submitted by the General Contractor during the submittal process. Concrete pavement must include steel reinforcement to limit shrinkage cracking, limit the width of transverse cracks, and limit long term deterioration common in cracked unreinforced concrete pavement. In the Austin area, concrete parking lot pavement is commonly designed to 26

29 have #3 steel reinforcement bars at 18-inch spacing in both directions. Alternatively, the project team can use the drag formula described in ACI 330R. Steel reinforcement must ideally be interrupted at the contraction joints (not passed into adjacent panel) except between perimeter panels and the next row of interior panels where alternating bars can cross the joint to serve as tie-bars. At other joint locations, if steel is placed through (under) contraction joints, then the pavement becomes a CRCP (continuously reinforced concrete pavement) and becomes more susceptible to shrinkage cracking, punchouts, and spalling. Note that steel reinforcement should have at least 2 inches of cover. Ideally, the reinforcement should be placed 2 inches below top of pavement (ACI 330R-2.8.1; ACI R.4.6). If irregular shaped panels (neither square nor rectangular) are planned in some areas of the parking lot, these panels should be reinforced regardless of the joint spacing. Construction joints may have to be formed if necessary during construction and should line up with a planned contraction joint. Dowels can be used to transfer load between concrete panels, to reduce the chance of joint faulting, and to limit deflections and damage to panel edges when supporting high volume truck loads. Minimum 24-inch long, 3/4-inch diameter smooth steel dowels, spaced 18 inches apart should be placed between panels. Dowels are typically placed in the middle of the vertical pavement section and must be properly horizontally aligned. Reinforcement, dowel, and joint details should be in accordance with the American Concrete Institute (ACI) or Portland Cement Association (PCA) guidelines. Curb-and-gutter concrete elements must be tied to the concrete pavement using tie-bars wherever there is a downward slope behind the curbline (i.e. slope to a detention pond). Clay slopes will creep downhill over time, causing severe separation cracking between the curb and the concrete pavement unless the two elements are tied together. PAVEMENT MAINTENANCE Flexible pavements are generally designed by geotechnical engineers to provide a 20-year service life before requiring an extensive rehabilitation, and only if proper maintenance is performed. The actual service life of a pavement until full reconstruction is actually performed by the Owner, however, is commonly 40 to 60 years. Regular maintenance can help extend the design 20-year service life. 27

30 Depending on the moisture content fluctuations within the subgrade, the flexible pavement may develop cracks or separations prematurely. Periodic crack sealing, fog seals, and slurry seals are to be expected and must be performed to maintain the service life and maintain the quality of the pavement by preventing water from infiltrating into the subgrade and by maintaining the quality of the surface. The 20-year service life assumes that the Owner will perform at a minimum an evaluation every two (2) years and perform crack sealing as necessary. It is also assumed that a thick asphalt seal coat or slurry coat will be placed as needed but at least three times during the 20 year service life. A primary cause for deterioration of hot mix asphalt pavement is oxidative aging that results in brittle HMA. Preventative maintenance (crack sealing, fog seals, slurry seals, and chip seals) will provide a protective seal or rejuvenate the asphalt binder to extend the life of the HMA. If concrete pavement is used, the Owner should anticipate performing a crack and joint cleaning and sealing operation at least twice during the first 20 years of service (e.g. every 7 years). Diamond grinding can be considered at 8 to 10 year intervals if pavement smoothness needs to be restored (re-leveling areas that exhibit joint faulting or other irregularities) and there are no issues with drainage, inadequate doweling (load transfer), structural integrity, weak subgrade with an inadequate pavement section design, D-cracking, and reactive aggregates, since such issues would have to be addressed (repaired) before spending time, money, and effort on grinding to restore levelness. PAVEMENT MATERIAL RECOMMENDATIONS AND TESTING Selection, transportation, placement, and compaction of pavement materials should be performed in accordance with locally developed guidelines (e.g. City of Austin Standard Specifications, Series 200 and 300). Subgrade Preparation 1. Pavement subgrade must be clear of organic matter. Soil improvement should be performed as recommended in this report. 2. Pavement subgrades that have local depressions resulting from uneven cut grading or filling or from equipment traffic (ruts) can lead to ponding of water within the flexible base layer in that area and subsequent premature loss of subgrade support. Forming and maintaining a subgrade that is level, smooth, and constructed to required grade is 28

31 important to produce proper drainage of the base course layer above the less permeable soil subgrade. The General Contractor and the earthwork or paving subcontractors must inspect the subgrade for any depressions before placing the first lift of flexible base course. 3. The contractor should have a mix design performed using the actual site soils and the stabilizing agent (lime, fly ash, cement). Scheduling should allow two weeks for the mix design (e.g. lime series) to be completed prior to construction. 4. Stabilizing agents (lime, fly ash, cement) must come from the same source as used in the mix design. If a new source is selected, particularly for lime, a new mix design is required. 5. High calcium quicklime shall conform to the requirements of ASTM C977 and C Lime stabilization design and construction should conform to local, state or federal government guidelines. Examples include: City of Austin Standard Specifications Series 200 Item 203S; TxDOT Specification Item 260; U.S. DOT FHWA Lime in Soil Stabilization, Publication FHWA-HI The basic procedure for lime stabilization is listed below: 1. Spread lime (either hydrated lime slurry or dry quicklime) 2. Slake (add water) if quicklime is used 3. Mix 4. Compact 5. Mellow 6. Remix 7. Final compaction 8. Cure Water must be applied periodically to keep the moisture content of the treated soil above optimum. Water is a key ingredient for the chemical reactions and the mixture must not be allowed to have insufficient water. Stabilization should extend horizontally 1 foot or more beyond the edge of the curb and gutter. 9. Item 203S of the City of Austin Standard Specifications addresses the construction of lime stabilized soil. Moisture content of the soil-lime mixture should be between the optimum 29

32 moisture content and 4 percentage points above optimum moisture content at the time of compaction. The moisture content must be maintained until pavement is placed. 10. Inspection of lime stabilized clay (if applicable) should include documentation of observations of the method of mixing, the uniformity of mixing, time period between lime application, mixing, and placement, and measurements of relative compaction and moisture content at the time of compaction. Atterberg limits tests should be performed to assure that the PI of the lime stabilized mixture is below 20 during the mellowing period. Phenolphthalein alcohol indicators can be used to determine the depth of subgrade that was actually treated. 11. Stabilized clay should be left undisturbed to mellow for at least two days after completion of the scarifying, lime placement, mixing, and sealing operation, or until the PI is reduced to below 20. Occasional water sprinkling may be required to keep the surface of the lime stabilized soil damp. Once mellowing is complete a final mixing should be performed followed by compaction. In-place moisture-density tests should be performed to confirm proper construction. The compacted stabilized clay should be left undisturbed and allowed to cure for a minimum of two days or until trucks can be supported without deflecting the subgrade. The surface should be kept moist during final curing and be kept moist until placement of the overlying pavement material. Alternatively a bituminous seal coat can be applied to protect the stabilized material from drying due to evaporation of moisture. 12. Clay stabilized with dry quicklime should be left undisturbed and allowed to cure for a minimum of four days after the final scarifying and compaction operation has been completed. 13. Of locally available geogrid we recommend the Tensar TX5 because it is ideally suited to the desired function of limiting cracking under swelling and shrinkage conditions and limiting cracking under soft subgrade conditions. A biaxial geogrid or an approximate equivalent from another manufacturer approved by Capital Geotechnical may also be considered but must be submitted for approval. Biaxial geogrid should meet the requirements of TxDOT DMS-6270: Biaxial Geogrid for Environmental Cracking. Geogrid must be installed per manufacturer requirements. Sheets of geogrid must overlap at least 18 inches because of the lack of restraint associated with the edge of a sheet. Overlaps of geogrid should be installed with attention being given to which direction the earth moving equipment will be pushing the overlying soil; i.e. use a shingle type overlap pattern in one direction to avoid displacing or lifting a geogrid at the overlaps during fill placement. If construction is performed when the subgrade soils are relatively moist (soft), a geotextile can be installed to serve as a filter fabric to maintain separation of the finer-grained 30

33 subgrade soil and the base material during installation of the geogrid and base course. Installation of geogrid and base on moist soft subgrade can be difficult if not properly performed, and the use of a geotextile separator can facilitate the process. 14. The subgrade should be scarified to the required depth and mixed with the stabilizing agent at the specified concentration until a uniform blend of soil, stabilizing agent, and water is achieved. Flexible Base Course 1. Flexible base material should be selected, placed, and compacted in accordance with Series 200, Section 210S, of the City of Austin Standard Specifications. Placement should not start until the subgrade is properly prepared and inspected. 2. Flexible base course should extend horizontally to at least the outside edge of the curband-gutter. 3. Flexible base should be placed in maximum 6-inch lifts and should be compacted to achieve a relative compaction of 100% or higher if using the maximum dry density determined by the Tex-113-E method, or 95% or higher if using the ASTM D 1557 Proctor method. Moisture content of the flexible base course material should be within two percentage points of the optimum moisture content at the time of compaction. Section 210S.5 of Series 200 of the City of Austin Standard Specifications addresses compaction of flexible base course. 4. Flexible base course should be tested during placement to document thickness, moisture content, and density at the time of compaction. 5. Crushed recycled concrete can only be considered if the recycled concrete was not contaminated by calcium sulfate industrial by-products. Hot Mix Asphalt 1. Hot mix asphalt should be selected, placed, and compacted in accordance with Item 340 of the City of Austin Standard Specifications. Hot mix asphalt surface course can be a TxDOT Type D gradation ( fine surface mix) for parking lots. Item 340 addresses specific material ingredient properties and gradations, as well as production and placement of HMA. 31

34 2. A prime coat should be applied on the underlying flexible base. 3. HMA paving should only be performed when the air temperature is above 40 degrees Fahrenheit. 4. Hot mix asphalt should be compacted to achieve a relative compaction between 92% to 96% of maximum theoretical density. 5. Inspection of hot mix asphalt should include placement temperature and thickness during installation. 6. The surface must be sealed with a finish roller before the mix cools to F. Concrete Pavement The critical factors affecting the performance of concrete pavement are the strength and quality of the concrete, proper placement of reinforcing steel for crack control, proper jointing for crack control, and the uniformity of the subgrade. A. For rigid pavement, concrete mixing, batching, forming, placing, finishing, and curing should generally conform to the guidelines described in the City of Austin Standard Specifications Series 300 Item 360: Concrete Pavement. Placement should not start until the subgrade is properly prepared and inspected. B. Concrete should consist of a minimum 500 psi flexural strength concrete at 28 day age. To achieve this flexural strength, a mix with a 28-day compressive strength of 3,500 psi or 4,000 psi may be required (i.e. do not order 3,000 psi concrete). C. Curing and protection procedures should be implemented to protect the pavement from moisture loss, rapid temperature change, and physical disturbance. D. Concrete should be sampled and field tested by a representative of Capital Geotechnical. E. Curing protection and procedures must be implemented to protect the concrete from moisture loss, rapid temperature change, freezing, and physical disturbance. F. All joints should be properly sealed with a backer rod and approved joint sealant. 32

35 SURFACE DRAINAGE, VEGETATION, AND UTILITY CONNECTIONS Performance of foundation slabs, pavement, and flatwork is influenced by changes in subgrade moisture conditions. We recommend the following precautions be implemented during construction: A. Utility structures that connect to the building should be designed to be flexible enough to tolerate some differential soil movement. Water supply pipes and sanitary sewer pipes beneath the slab should be placed in long sections with as few joints (leak-prone) as possible and should be of durable size and material. Utilities that penetrate the foundation slab should be designed with either some degree of flexibility or with sleeves in order to prevent damage or leaking should vertical movement occur (i.e. shower or bathtub drain). Water supply and sanitary sewer systems should be leak tested after installation. Telescoping joint or swivel joint pipe fittings can be considered. If a structurally supported slab is used, water lines should preferably be run above the slab within the framework. Sanitary sewer lines should preferably be hung in a trench along the pipe alignment using pipe hangers and wire tied to the horizontal rebar of the slab. The trench depth must be adequate to maintain the required void space (i.e. 8 inches) beneath the pipe. B. The ground surface, pavement, and flatwork around the building should be sloped away from the building to provide positive drainage away from the building perimeter. A minimum drop of 6 inches over the first 10 feet from the edge of the foundation is recommended (IBC 2012: ). C. Roof drains should be designed and placed to discharge stormwater at least five feet away from the building unless pavement abuts the edge of the building at the discharge location. Roof drain downspouts should also be concentrated on the downslope side of the building. D. If concrete root barriers are not installed, trees or deep-rooted bushes should not be planted or allowed to exist adjacent to the building within a distance equal to half of their mature height because of the root penetration and moisture demand that will dry the underlying clay soils. Cracks in surrounding pavement or sidewalks should be routinely sealed to prevent surface water from infiltrating into the subsurface clay soil. Trees should also not be planted near pavement or flatwork unless a root barrier is installed. E. Plants placed close to the foundation should be limited to those with low moisture requirements (do not encourage high rates of irrigation). 33

36 F. Air conditioner condensation outlet pipes should preferably on the downslope side of the building or into a controlled drainage system. G. If shrubs must be placed adjacent to the building, the landscape beds or planters should not be recessed (place at grade or elevate above grade and drain properly to prevent ponding adjacent to the foundation slab). H. If an exterior sprinkler system is installed to water landscaping, the sprinkler lines should not be placed within 5 feet of the edge of the foundation. Instead the lines should be placed so that sprinkler heads with sufficient capacity are used and direct water toward the structure from 5 feet away. I. Leak tests should be periodically performed on water supply, sprinkler, and sewer systems to determine if a leak exists. Any leaking pipes should be repaired as soon as possible to stop the increase in moisture content in the underlying clay soils. The water supply system can be easily checked by monitoring the water meter when no water is being used. J. Landscape islands in parking lot pavement are sources of water infiltration into adjacent pavement subgrade and base material. Islands should consist of self-contained planters (geomembrane liner or concrete cutoff elements), or drains should be installed to collect excess rainwater and discharge to the storm sewer system. Weep holes can be drilled through the curb to help prevent ponding of water behind the curbline and limit water infiltration into the subgrade under the pavement. POST-TENSIONING (IF USED) Post-tensioning cables (tendons) and accessories need to be accurately placed, protected, and correctly installed. Utility penetrations through the slab must be planned in conjunction with the placement of post-tensioning cables. The Structural Engineer, or the Geotechnical Engineer if needed, should be retained to perform a pre-pour inspection to observe and document grade beam dimensions and proper cable installation. Pulling (tensioning) of cables should be performed by experienced personnel because of the danger involved during the pulling and lock-off operation. Cable ends must be properly covered or coated to prevent corrosion that can allow long term relaxation and reduction of design strength, and potential excessive movement in isolated areas of the slab. Tendon tails should not be cut until the tensioning (stressing) test data is approved by the project Structural Engineer. The posttensioning stressing operation should be observed by the Structural Engineer (or by the 34

37 Geotechnical Engineer if needed) to document proper construction. Observations should include obtaining a copy of the calibration sheet correlating force and hydraulic pressure of the jack being used. Each tendon elongation should be measured and compared to specification requirements. Results can then be provided to the project Structural Engineer for approval. LIMITATIONS This report is subject to the limitations and assumptions presented in the report. Should conditions change or if assumptions are not accurate, we must be contacted to review our recommendations. Borings were spaced to obtain a reasonable indication of subsurface conditions. The data from the borings is only accurate at the exact boring locations. Variations in the subsurface conditions not indicated by our borings are possible. The recommendations in this report were developed considering conditions exposed in the exploratory borings and our understanding of the type of structure planned. We believe that the geotechnical services for this project were performed with a level of skill and care ordinarily used by geotechnical engineers practicing in this area at this time. No warranty, express or implied, is made. Capital Geotechnical Services should be retained to review plans and specifications related to geotechnical elements of the construction to check that our recommendations have been properly interpreted. Capital Geotechnical Services cannot be responsible for incorrect interpretations of our recommendations, particularly if we are not retained to review plans and specifications. This report is valid until site conditions change due to disturbance (cut and fill grading) or changes to nearby drainage conditions, or for 3 years from the date of this report, whichever occurs first. Beyond this expiration date, Capital Geotechnical Services shall not accept any liability associated with the engineering recommendations in the report, particularly if the site conditions have changed. If this report is desired for use for design purposes beyond this expiration date, we recommend drilling additional borings so that we can verify the subsurface condtions and validate the recommendations in this report. 35

38 INSPECTIONS Capital Geotechnical should be retained to perform the field observations, field testing, and laboratory testing recommended in this report (i.e. City of Austin Special Inspections ) because of our familiarity with the project and site conditions. The performance of foundations and pavement is primarily controlled by the quality of the construction. To prevent misinterpretation of our recommendations, and to document proper construction, Capital Geotechnical should be retained to perform quality control (QC) testing, inspection, and documentation during earthwork and during construction of the foundations and pavement. Quality control (QC) inspections by Capital Geotechnical Services can include (as applicable depending on design): Sampling and lab testing of proposed fill material to check and document classification. Inspection of soil improvement excavation or soil improvement injection operation. Testing of compacted fill, pavement base material, or lime stabilized clay subgrade in-place to check and document proper compaction and moisture-conditioning. Inspection and documentation of drilled shaft construction. Pre-pour inspection to check and document grade beam dimensions, void box installation (if applicable), reinforcing steel installation, and moisture vapor barrier installation (if not performed by Structural Engineer). Pre-pour inspection of post-tension cable installation (if not performed by Structural Engineer). Concrete sampling and testing to document as-built condition of wet concrete and to document that the supplier provided an adquate mixture to the site. Post-tension cable stressing inspection (if not performed by Structural Engineer). Pre-pour inspection of concrete pavement contruction (reinforcing steel, joint layout, joint doweling, thickness). 36

39 Site Area Vicinity Map Hotel at Burnet Rd (MoPac) Austin Travis County, Texas Prepared By: NFK Base Map By: City of Austin Capital Geotechnical Services PLLC Austin, Texas Scale: - Date: October 2015 Project #: Figure #: 1

40 Subject Lot Local Lot Plan Hotel at Burnet Rd (MoPac) Austin Travis County, Texas Prepared By: NFK Base Plan By: Travis County Capital Geotechnical Services PLLC Austin, Texas Scale: - Date: October 2015 Project #: Figure #: 2

41 Old Burnet Rd (now under MoPac mainlaines) Site Area Kdr : Clay sedimentary deposit categorized as the Del Rio Clay geologic formation. Kgt : Limestone rock and marly limestone sedimentary deposit categorized as the Georgetown Limestone geologic formation. Geology Map Hotel at Burnet Rd (MoPac) Austin Travis County, Texas Prepared By: NFK Base Map By: U.T. Bureau of Econ. G. Capital Geotechnical Services PLLC Austin, Texas Scale: - Date: October 2015 Project #: Figure #: 3