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HomeMy WebLinkAboutATC Report of Geotechnical Investigation - Lindsay Meadows Subdivision W....pdfIV AV 0 A Tkc ENVIRONMENTAL• GEOTECHNICAL BUILDING SCIENCES • MATERIALS TESTING 7606 Whitehall Executive Center Drive. Suite 800 Charlotte, NC 28273 Tel: 704-529-3200 Fax:704-529-3272 www.atcassociates.com REPORT OF GEOTECHNICAL EXPLORATION Lindsay Meadows Subdivision Waxhaw, North Carolina ATC Project No. 199CAR1808 Prepared For: Mr. Hamilton Stolpen American Homes 4 Rent 18805 W. Catawba Avenue, Suite 102 Cornelius, NC 28031 Prepared By: ATC Associates of North Carolina, P.C. 7606 Whitehall Executive Center Drive, Suite 800 Charlotte, North Carolina 28273 July 3, 2018 IF AV Tc ENVIRONMENTAL• GEOTECHNICAL BUILDING SCIENCES • MATERIALS TESTING July 3, 2017 Mr. Hamilton Stolpen American Homes 4 Rent 18805 W. Catawba Avenue, Suite 102 Cornelius, NC 28031 Subject: Report of Geotechnical Exploration Lindsay Meadows Subdivision Waxhaw, North Carolina Project No. 199CAR1808 Dear Mr. Stolpen: 7606 Whitehall Executive Center Drive, Suite 800 Charlotte, NC 28273 Telephone 704-236-1259 Fax 704-529-3272 www.atceroupservices.com ATC Associates (ATC) is pleased to submit this report providing engineering analysis for the proposed single family development in Waxhaw, North Carolina. This report, which details the results of our geotechnical exploration for the referenced project, summarizes the project information provided to us, describes the site and subsurface conditions encountered, and details our geotechnical recommendations for the project. The Appendix contains a Boring Location Plan and Soil Boring Logs. We appreciate the opportunity to be of service to you for this phase of the project. If you have any questions concerning this report, please call us. Respectfully Submitted, ATC SSOCIATES OF NORTH CAROLINA, P.C. Brian Carpenter, P.E. Project Engineer r �/�/ Le�teetettgFt;?r Joseph G. Schold, P.E. fa SEAL Reg. NC No. 21736 Principal Geotechnical Engineer o� Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision TABLE OF CONTENTS 1.0 INTR OD UC TION.................................................................................................................... 2 1.1 Project Information...................................................................................................................2 1.2 Purpose and Scope of Exploration...........................................................................................2 2.0 EXPLORATION PROCEDURES AND FINDINGS............................................................. 4 2.1 Exploration Procedures............................................................................................................4 2.2 Site Geology................................................................................................................................4 2.3.3 Groundwater Conditions............................................................................................................7 2.4 Laboratory Testing....................................................................................................................7 2.4.1 Soil Classification.......................................................................................................................7 2.4.2 Moisture Contents.......................................................................................................................7 3.0 FOUNDATION SUPPORT AND RECOMMENDATIONS................................................. 8 3.1 Site Development Considerations and Recommendations.....................................................8 3.2 Shallow Foundation Design Recommendations......................................................................9 3.3 Floor Slabs..................................................................................................................................9 3.4 Slope Stability..........................................................................................................................10 3.5 Groundwater Conditions and Control..................................................................................10 3.6 Retaining/Below Grade Walls................................................................................................10 4.0 SITE PREPARATION........................................................................................................... 14 4.2 Wet Weather Construction.....................................................................................................16 5.0 CONSTRUCTION CONSIDERATIONS............................................................................. 18 6.0 GENERAL AND LIMITATIONS......................................................................................... 19 APPENDIX.................................................................................................................................. 20 APPENDIX Important Information About Your Geotechnical Report Soil Test Boring Location Plan Test Boring Logs Reference Notes for Boring Logs ATC Project No. 199CAR1808 i Report of Geotechnical Exploration Lindsay Meadows Subdivision 1.0 INTRODUCTION 1.1 Project Information July 3, 2017 The property consists of one parcel totaling 17.385 acres located on the south side of Kensington Drive, east of Waxhaw-Marvin Road in the northern part of Waxhaw, North Carolina. The property is located along Kensington Drive in Waxhaw, Union County, North Carolina. According to information obtained from the Union County Geographic Information System (GIS), the property is comprised of one parcel identified as Parcel Number 06192007. The surrounding area is mostly residential with vacant wooded areas. The vicinity of the subject property is characterized by residential use to the north and south, with undeveloped land to the west and east and part of the Union County Waste Water Treatment Plant to the east. Local topography slopes to the south towards Twelve Mile Creek, which runs along the southern property boundary. The property is currently mainly vacant heavily wooded land, with cleared areas in the northern part along Kensington Drive. It is our understanding construction at the site will consist of numerous single and two-story residential structures, MSE retaining walls, utility infrastructure, and parking facilities and drives. A summary of the anticipated site construction is provided below. Project Details Single and Two Story Above -Grade Residential Structures Wood Framing and Masonry Block Estimated Design Column Loads Less than 20 - 40 Kips Estimated Wall Loads 2 to 6 kips per foot Approximate Maximum Mass Excavation Cut and Fill Depths Less than 10 feet Design Traffic Loads Light to Medium Duty 1.2 Purpose and Scope of Exploration The purpose of this exploration was to obtain subsurface data at the project site to provide geotechnical engineering recommendations for the project. Services performed under this agreement included the drilling of the soil test boring and preparation of a geotechnical engineering report. The subsurface investigation data obtained for this study and related plans are presented for the proposed single family residential structures, associated utilities, and parking facilities and drives. Scope of Services Summary Description of the site and presentation of subsurface test boring data, including Boring Location Plan and Soil test Boring Logs. Depths, thicknesses, and composition of soil strata that will be impacted by the planned site construction. ATC Project No. 199CAR1808 2 Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision Depth of topsoil encountered at the site. Recommendations pertaining to site development including site preparation, earthwork construction, unsuitable soils, groundwater control, excavation slopes, and difficult excavation. Depth and presence of rock on -site and recommendations regarding rip -ability and blast -ability of the rock. Recommendations regarding the on -site use of any rock encountered on site. Depths to encountered groundwater and soil strata that could affect the proposed construction. Recommendations for control of groundwater in design and during construction. Recommendations for foundation support of the proposed structures, including allowable bearing pressures, and design parameters for use by other design professionals. Soil design parameters are included for design to resist lateral loads and overturning. Recommendations for floor slab support. Recommendations regarding the suitability of the on -site cut soils with regard to use on site for general grading, retaining wall backfill, pavement construction, utility backfill, etc. Laboratory testing of on -site including in -situ moisture contents, gradations, and Atterberg Limit tests. Recommendation for the design and construction of light and heavy duty pavements. Recommendations regarding the suitability of the on -site cut soils with regard to use on site for general grading, retaining wall backfill, pavement construction, and utility backfill. Comments and recommendations regarding geotechnical construction considerations related to preparation of the construction plans and specifications. Our scope of services did not include recommendations for unsupported excavation slopes, stormwater management, erosion control, detailed cost or quantity estimates, final plan and specification documents, and construction observations and testing. Any statements in this report regarding odors, colors, or unusual or suspicious items or conditions are strictly for the information of the client. ATC Project No. 199CAR1808 3 Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision 2.0 EXPLORATION PROCEDURES AND FINDINGS 2.1 Exploration Procedures ATC performed eighteen soil test borings, designated B-01 through B-21. The Standard Penetration Testing (SPT) borings extended to depths of 20 feet below the existing ground surface. The referenced boring locations were established in the field by an ATC engineer by measuring distances and estimating right angles from existing site features shown on a conceptual site plan provided by your office. All soil sampling and standard penetration testing (SPT) were in general accordance with ASTM standard D 1586. The borings were advanced by hollow -stem rotary drilling techniques. At regular intervals, soil samples were obtained with a standard 1.4-inch I.D., 2.0-inch O.D., split -barrel sampler. The sampler was first seated 6 inches and then driven an additional foot with blows of a 140-pound hammer falling 30 inches. The number of blows required to drive the sampler the final foot was recorded and is designated the "standard penetration resistance." Because the sampler may be damaged by driving it a foot into very dense soils, it is driven a few inches into such materials and the penetration resistance is expressed as the number of hammer blows versus the depth of penetration, e.g. 100/3", 50/1", etc. Penetration resistance, when properly evaluated, is an index of the soil's strength, density, and foundation support capability. Representative portions of the soil samples obtained with the split -barrel sampler were sealed in plastic bags and transported to our laboratory. In the laboratory, they were examined by a geotechnical engineer, classified in general accordance with the Unified Soil Classification System (USCS), and assigned laboratory testing. The soil descriptions and classifications are based on visual examination and should be considered approximate. Test Boring Records that present soil descriptions and graphically depict penetration resistance and observed groundwater levels are included in the report Appendix. Occasionally, boreholes will collapse preventing water level measurements. Groundwater levels were measured in the boreholes at the completion of drilling operations. The groundwater elevations are indicated herein and on the Boring Logs in the Appendix. 2.2 Site Geology According to the USGS Topographic 7.5-Minute Series Catawba NE, South Carolina quadrangle map, dated 2014, and the Waxhaw, North Carolina quadrangle map, dated 2013, the property is located in an area with an approximate elevation range from 490 feet above mean sea level (MSL) along the creek in the southern part of the property to 550 feet above MSL in the northern part of the property. The property slopes to the south towards Twelve Mile Creek, which runs along the southern property boundary. According to the Geologic Map of North Carolina, the property is located in the Piedmont Physiographic Province, and the rock type beneath the site consists of metavolcanic tuffs and flow rock. The shallow subsurface in most areas of the Piedmont contains residual soil overburden, including structure -free residuum, saprolite, and partially weathered rock (PWR) that derive from in -place weathering of the crystalline bedrock. In areas near creeks and rivers, alluvium derived from weathered residual soil is often present and such material may be present near drainages at the property. Saprolite and PWR typically contain some relict structures from the original rock material. Depth to rock ranges from ground surface at occasional outcrops to depths of up to 100 feet in areas of easily weathered rock. ATC Project No. 199CAR1808 4 Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision According to information obtained from the United States Department of Agriculture (USDA) Soil Conservation Service (SCS) Web -Based Soil Survey, the property is primarily underlain by Tarrus gravelly silty clay loam and Chewacla silt loam. Tarrus gravelly silty clay is well drained and located on hillslopes on ridges. A typical soil profile consists of gravelly silty clay loam to 6 inches below ground surface (bgs), silty clay from 6 to 45 inches bgs, and weathered bedrock from 45 to 80 inches bgs. Permeability is very low to high, and the available water capacity is low. Chewacla silt loam is somewhat poorly drained and located on floodplains. A typical soil profile consists of silt loam to 4 inches bgs, silty clay loam from 4 to 26 inches bgs, loam from 26 to 38 inches bgs, clay loam from 38 to 60 inches bgs, and loam from 60 to 80 inches bgs. Permeability is moderately high to high, and the available water capacity is high. 2.3 Subsurface Conditions The procedures used for boring advancement and sample classification are included in the Appendix. The subsurface materials encountered were classified using the USCS. The soil test boring logs, which detail the subsurface conditions encountered in the borings, are included in the Appendix. The field portion of ATC's geotechnical exploration consisted of fifteen soil test borings to depths of 5.5 to 15 feet below the existing ground surface elevations. Three generalized subsurface strata were encountered within the termination depths and the soil strata are summarized as follows: Approximate Maximum Depth to Materials Encountered Consistency / Relative Description Bottom of Stratum (ft.) Density Stratum A — 0 to 13.5 feet Reddish brown and brown lean SPT Blow counts of 12 to 73 Residuum Soils CLAY and elastic SILT (CL and bpf MH) Stratum B — 0 to 15+ feet White, brown, and silty SAND SPT Blow counts of 22 bpf to Residuum Soils (SM) 50 blows for 6-inches of penetration Stratum C — 4.5 to 20+ feet Sampled as white brown, SPT Blow counts of 50/6" to Partially Weathered brown, and tan silty sand 50/0" Rock 2.3.1 Topsoil Topsoil depths encountered at the site ranged from approximately 6 to 12 inches in depths. Due to the heavy vegetation and potential water features on site, we expect topsoil depths to be higher in some areas of the site. 2.3.2 Residual Soils The residual soils encountered at the site consisted of stiff to hard sandy low and high plasticity SILTS (ML and MH) and lean CLAYS (CL) in the near surface soils. Underlying the fat clays, the borings encountered medium dense to very dense silty SANDS (SM). ATC Project No. 199CAR1808 5 Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision 2.3.3 Partially Weathered Rock (PWR) Weathered bedrock materials encountered during the drilling operations are summarized in the Table below. Boring No. Approximate Depth to Surface of PWR (ft.) Auger Refusal Depth, ft. B-01 5.5+ 5.5 B-01A 6+ 6 B-02 6 — 11 11 B-02A 9+ 9 B-03 10 - 14 14 B-04 3.5 — 10.5 10.5 B-04A 13+ 13 B-05 2.5 — 7.5 7.5 B-05A 7+ 7 B-06 13.5 — 15 Terminated at 15 feet B-07 4-15 Terminated at 15 feet B-08 2.5 —10 10 B-08A 9+ 9 B-09 13.5+ 13.5 B-10 2.5 — 13.7 13.7 B-11 Not Encountered NA B-12 7.5 —12 12 B-13 1-6 6 B-13A 5+ 5 B-14 2.5-5 5 B-14A 6-9 9 B-15 3-7 7 B-15A 7+ 7 ATC Project No. 199CAR1808 6 Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision 2.3.3 Groundwater Conditions Groundwater was not encountered during drilling operations. Generally, seasonal and yearly fluctuations of the water table should be expected with variations in precipitation, surface runoff, evaporation, pumping, and other similar factors. 2.4 Laboratory Testing 2.4.1 Soil Classification Soil classifications provide a general guide to the engineering properties of various soil types and enable the engineer to apply past experience to current problems. In our explorations, samples obtained during drilling operations are observed in our laboratory and visually classified by an engineer. The soils are classified according to consistency (based on number of blows from standard penetration tests), color and texture. These classification descriptions are included on our Test Boring Records. The classification system discussed above is primarily qualitative; laboratory testing is generally performed for detailed soil classification. Using the test results, the soils were visually classified according to the USCS (ASTM D 2487). This classification system and the in -place physical soil properties provide an index for estimating the soil's behavior. The soil classification and physical properties obtained are presented in this report. The results of the Atterberg Limit testing is provided below. Laboratory Test Results 2.4.2 Moisture Contents The moisture content is the ratio expressed as a percentage of the weight of water in a given mass of soil to the weight of the solid particles. This test was conducted in general accordance with ASTM D 2216. The test results are presented on the Boring Logs in the Appendix. ATC Project No. 199CAR1808 Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision 3.0 FOUNDATION SUPPORT AND RECOMMENDATIONS Soil data obtained during this subsurface exploration have been used to estimate the shearing strength and deformation characteristics for the subsurface soils encountered at the site. These parameters have been used as guidelines for foundation system design and to estimate potential settlement due to the anticipated site construction and foundation loading. The engineering analysis based on these parameters was performed in accordance with generally accepted engineering principles and practices. 3.1 Site Development Considerations and Recommendations A grading plan was not available for review during preparation of this report, therefore we have assumed cuts at the site to be less than 5 feet in depth. Additional evaluation of the site may be performed by ATC after review of the site grading plans. Based on the laboratory testing performed, the site contains some near surface high plasticity "elastic" SILTS and lean CLAYS (CL). These soils were generally encountered in the upper 4 to 6 feet of the subsurface profile. The plasticity of the elastic SILT soils was moderately high (PI's above 50 percent) making the near surface elastic SILT's marginally suitable for use with the upper 3 feet below the proposed building foundations. These soils may be very difficult to work with in wet and cool periods and these soils will also become unstable when exposed to wet weather and/or heavy construction traffic like that associated with mass clearing and grading operations. Therefore, undercut excavation, mechanical drying, and/or chemical stabilization should be expected during and at the completion of the grading operations. If the soils are stable, as determined by the geotechnical staff based on evaluation by proofrolling and DCP testing, they may remain in -place as bearing materials for fill placement. However, again the use of these soils within two feet of the foundation bearing elements is not recommended due to the potential for shrink/swell and/or excessive foundation settlement due to soil softening. Given the results of the soil test borings as noted in the Table on page 6 of this report and the general geology of the site, weathered rock is expected across the site at relatively shallow depths. It is also expected that the rock surface maybe highly variable in depth. For the weathered rock materials encountered, we expect these materials to be excavatable in mass cutting and filling operations using standard to large sized construction equipment. For trench rock excavations, rock hammers may be required above the noted "Auger Refusal" depths. For excavations below the "Auger Refusal" depths, blasting may be required. We recommend performing a series of Test Pit excavations at the site, in projected "deep cut" areas of the site prior to the commencement of the site construction in order to help determine the "excavatability" of the weathered rock materials. ATC Project No. 199CAR1808 8 Report of Geotechnical Exploration Lindsay Meadows Subdivision 3.2 Shallow Foundation Design Recommendations July 3, 2017 Based on the anticipated site conditions, it appears the planned residential structures may be constructed using shallow foundation systems. Based on the site findings, the proposed structures may be supported on shallow foundations bearing on competent soils and may be proportioned based on an allowable net soil bearing pressure of 2,000 pounds per square foot (psf). The presented allowable bearing capacity includes a factor of safety of at least 3.0. Description Columns Walls Net allowable soil bearing pressure' 2,000 psf 2,000 psf Minimum dimensions 30 inches 18 inches Minimum protective embedment 18 inches 18 inches Approximate total settlement <1 inches <1/2 inches over 50 feet The recommended net allowable soil bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. This bearing capacity assumes that any fill or soft soils, as noted herein and as encountered, will be undercut and replaced with compacted engineered fill in accordance with the recommendations provided herein. The extent of any required site undercutting should be determined in the field by experienced geotechnical personnel based on site conditions at the time of construction. Resistance to lateral loads for shallow foundations will likely be provided by frictional resistance between the base of the concrete footings and the underlying structural fill. We recommend that an ultimate friction factor of 0.45 be used for the design. Additional resistance to lateral loads will be provided by passive pressure of the granular backfill adjacent to the perimeter of the footings. A passive resistance modeled by an equivalent fluid unit pressure unit weight of 300 pcf may be used for soil against the edge of the footing. This is an ultimate value. All backfill placed against the edge of the footings must be properly compacted as indicted herein and the upper 18 inches of soils be not be included in the passive pressure calculations. 3.3 Floor Slabs For ground -level floor slabs placed at the site, we recommend the floor slabs be supported on low plasticity residual soils or engineered fill with a minimum of a 6-inch layer of compacted Aggregate Base Course material (ABC) or a 4-inch layer of washed stone (NC DOT No. 57 or 67 gradation), as well as a vapor barrier, should be provided beneath all building floor slabs to provide a capillary break and to help prevent a damp slab condition. ATC Project No. 199CAR1808 9 Report of Geotechnical Exploration Lindsay Meadows Subdivision 3.4 Slope Stability July 3, 2017 Our exploration did not include a detailed analysis of slope stability for any temporary or permanent condition. We recommend temporary slopes no steeper than 1.0(H):1.0(V) and permanent slopes no steeper than 2.0(H):1.0(V) for construction in existing natural soils or new structural fill placed in accordance with our recommendations. In building areas, minimum top of slope setbacks of 10 feet and 5 feet are recommended, respectively. Slopes should be protected from erosion, and surface runoff should be diverted away from slopes. For erosion protection, a protective cover of grass or other vegetation should be established on permanent soil slopes as soon as possible. 3.5 Groundwater Conditions and Control Based on the site conditions, we do not anticipate that groundwater will be encountered during construction operations in low areas of the site, deep utility cuts, or in the area of the encountered water features. The seasonal conditions will also influence the groundwater conditions at the site. The contractor is responsible to assure adequate groundwater control is in -place and functioning prior to the start of any work then allowing all work to be performed in a dry (free from flowing or standing water) condition. The contractor is responsible to establish the means and methods of groundwater control and to include all such items in his bid and scope of work. In order to prevent adverse effects of groundwater to exposed subgrade materials, it has been our experience that groundwater levels when lowered and maintained at a depth of at least 3 feet below the limits of subgrade excavation and undercutting elevation typically provide a stable working platform. Additionally, the dewatering system should be in -place and functioning sufficiently prior to beginning earthwork construction within the area. Inadequate dewatering may cause the subgrade to destabilize under loads from earthwork equipment and be problematic in placement and compaction of fill soils. Rainwater and runoff that accumulate in footing excavations can be pumped out of small dug sumps. Groundwater levels are subject to seasonal, climatic and other variations and may be different at other times and locations than those stated in this report. A site drainage scheme should be implemented and maintained at all times by the contractor to redirect all off site drainage away from the limits of construction. Ponding or standing water may result in softening of soils that will require additional remedial work to facilitate construction. Installation of utilities below the water table will be problematic, requiring dewatering, if it is encountered. The contractor should be required to control this water such that the utilities can be constructed in the "dry". The utility joints should be covered with a drainage fabric such as Mirafi 180N, or equivalent, which should extend at least 12 inches beyond each side of the joint. 3.6 Seasonal High Groundwater Table Based on the results of the borings performed on site and the groundwater conditions encountered and the review of the site topographical data, we estimate a Seasonal High Groundwater Table Elevation of 495 to 500 feet MSL. ATC Project No. 199CAR1808 10 Report of Geotechnical Exploration Lindsay Meadows Subdivision 3.7 Retaining/Below Grade Walls July 3, 2017 Earth pressures on walls below grade are influenced by structural design of the walls, conditions of wall restraint, methods of construction and/or compaction, and the strength of the materials being restrained. The most common conditions assumed for earth retaining wall design are the active and at -rest conditions. Active conditions apply to relatively flexible earth retention structures, such as freestanding walls, where some movement and rotation may occur to mobilize soil shear strength. Walls which are rigidly restrained, such as basement, tunnel, or loading dock walls, should be designed for the at -rest condition. A third condition, the passive state, represents the maximum possible pressure when a structure is pushed against the soil, and is used in wall foundation design to help resist active or at -rest pressures. Because significant wall movements are required to develop the passive pressure, the total calculated passive pressure should be reduced by one-half for design purposes. Based on previous experience with similar soils and construction, we recommend the following earth pressure coefficients and equivalent fluid pressures for design of reinforced concrete retaining or below grade walls on this project: Earth Pressure Conditions Coefficient Recommended Equivalent Fluid Pressure, (Pcf) Active (Ka) 0.36 43 At -Rest (Ka) 0.53 64 Passive (Kp) 2.77 166 A moist soil unit weight of 120 pounds per cubic foot (pcf) should be used for design calculations. Our recommendations assume that the ground surface above the wall is level. A coefficient of friction value between soil and concrete of 0.35 is recommended. An allowable bearing pressure of 2,000 psf may be used for footings designed to bear on competent existing fill materials, residual soils, or new structural fills. The recommended equivalent fluid pressures assume that constantly functioning drainage systems are installed between walls and soil backfill to prevent the accidental buildup of hydrostatic pressures and lateral stresses in excess of those stated. If a functioning drainage system is not installed, then lateral earth pressures should be determined using the buoyant weight of the soil (approximately 58 pcf). Hydrostatic pressures calculated with the unit weight of water (62.4 pcf) should be added to these earth pressures to obtain the total stresses for design. Tractors and other heavy equipment should not operate within 10 feet of below grade walls to prevent lateral pressures in excess of those cited. If foundations or other surcharge loadings are located a short distance outside below grade walls, they may also exert appreciable additional lateral pressures that must be considered in design. ATC Project No. 199CAR1808 11 Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision These retaining wall/below grade wall recommendations should not be correlated with soil parameters for use in mechanically stabilized earth (MSE) wall design. We recommend that soil parameters for any MSE retaining wall design be established through appropriate laboratory testing by the wall designer. 3.8 Pavement Design and Construction Based upon our evaluation and analyses, the on -site soils should be acceptable for construction and support of a flexible (crushed gravel base) type pavement section after proper subgrade preparation as discussed in the Site and Subgrade Preparation section of this report, provided that adequate drainage controls are implemented. The subgrade should be compacted to a minimum depth of 12 inches to at least 95 percent of the Standard Proctor maximum dry density (ASTM D-698). Any fill utilized to establish the desired subgrade elevation should consist of approved structural fill uniformly compacted to a minimum density of 95 percent of the soil Standard Proctor maximum dry density (ASTM D-698). Base material should meet NCDOT requirements, including compaction to 100 percent of its maximum dry density as determined by the Modified Proctor Test (ASTM D-1557). To avoid rutting, traffic should not be allowed on the subgrade before the base is placed. As a guideline for pavement design, we recommend that the Aggregate Base Course (ABC) and crushed concrete base materials be a minimum of 8-inches in thickness. The following flexible pavement recommendations are based on an assumed California Bearing Ratio (CBR) value of 3 to 5. This value assumes the subgrade is prepared as discussed in this report. Flexible Pavement Structural Sections The following pavement designs are based upon the design methods described in the "AASHTO Guide for Design of Pavement Structures 1993" published by the American Association of State Highway and Transportation Officials (AASHTO). These designs present the recommended range of 18-kip-equivalent single axle loads for the "standard duty" and "heavy duty" pavement sections presented. Pavement Flexible Pavement Structural Sections Duty (15-year Design) Standard 1.5-inches Surface Course 8-inches of Compacted Aggregate Base 2.0-inches Intermediate Course Course (ABC) Heavy 1.5-inches Surface Course 8-inches of Compacted Aggregate Base 3.5-inches Intermediate Course Course (ABC) ATC Project No. 199CAR1808 12 Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision Concrete Pavement Structural Sections As an alternate to the above flexible pavement design, a rigid concrete pavement design could be used. It is recommended that the concrete pavement incorporate the following design criteria. Design Parameters Value Minimum Concrete Compressive Strength (psi) 4,000 psi at 28-days Minimum Concrete Modulus of Elasticity (psi) 3,600,000 Effective Modulus of Subgrade Reaction (pci) 150 Load Transfer Coefficient 3.8 Drainage Coefficient 1.0 Soil Subgrade CBR 3 to 5 The subgrade should be prepared to achieve a minimum California Bearing Ratio (CBR) of 3 to 5 to a depth of at least 12 inches below the concrete base elevation. The subgrade soils should be compacted to at least 95 percent of the Standard Proctor maximum dry density (ASTM D-698). The following pavement designs are based upon the design methods described in the "AASHTO Guide for Design of Pavement Structures 1993" published by the American Association of State Highway and Transportation Officials (AASHTO). These designs present the recommended range of 18-kip-equivalent single axle loads (ESALs) for the "standard duty" and "heavy duty" pavement sections presented below. Pavement Duty Rigid Pavement Structural Sections (15-year Design) Standard 6-inches Concrete 6-inches Crushed Aggregate Base Course (ABC) 4,000 psi (28 days) Heavy 7-inches Concrete 6-inches Crushed Aggregate Base Course (ABC) 4,000 psi (28 days) Dumpster Pads 8-inches Concrete 6-inches Crushed Aggregate Base Course (ABC) 4,000 psi (28 days) The above designs are based on assumed traffic volumes. If actual traffic volume and loading characteristics are provided at a later date, some modification to these designs may be required. ATC Project No. 199CAR1808 13 Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision The ABC should be compacted to at least 100% of the Modified Proctor (D-1557) maximum dry density. Based on our review of the minimum pavement design criteria and the pavement design procedures, the pavement structural sections presented appear to satisfy the minimum pavement design criteria. It is suggested that a rigid pavement be utilized in such areas as the dumpster locations, and in any other areas where dumpster trucks or other large vehicles load, back up, and turn around. 4.0 SITE PREPARATION 4.1 Compacted Fill Recommendations If organic laden soils are encountered at the site, the soils are general unsuitable for use in structural areas of the site. These soils also contains moderate to high plasticity SILTs (MH) that are marginally suitable for use as engineered fill on site. These soils are suitable for use in the planned parking areas and drives, if the soils are at moisture contents which will allow the soils to be compacted to at least 95 percent of the maximum dry density. Fill materials used to replace potential undercut areas, pipe backfill, or establish finished grades should meet the following criteria and should be generally free of deleterious materials and rock fragments larger than 6 inches in diameter. Fill materials should also be at moisture content that allows for the proper placement and compaction of the materials per the requirements provided herein. Fill materials to be used as backfill materials should be tested, prior to use, in order to determine the soils suitability and compaction characteristics. Fill Type USCS Classification Acceptable Locations for Placement On -site soils and residual low plasticity soils including silts, clays, and sands On -site soils and residual moderate to high plasticity soils including silts and clays M L, C L, SC, S P CH and MH with LL>60 and 13I<30 Acceptable fill material at all locations and elevations Acceptable as fill in pavement areas at least 2 feet below subgrade Imported Soils ML, CL, SM, SP, GW with LL<50 and Acceptable in all locations and uses PI<20 Fill materials should be free of large rock (greater than 6 inches in largest dimension) and organic materials (less than 3 percent by weight). The use of larger rock or asphalt fragments in structural fill must be carefully monitored and tested by the Geotechnical Engineer and/or his authorized representative. We recommend that the grading contractor have equipment on site during earthwork for both drying and wetting of fill soils. We expect that the on -site residual soils and some of the existing fill soils will be suitable for use as structural fill on the project. Fill materials should be tested to verify their suitability. We recommend that all fill materials have a dry unit weight of at least 95 pcf. ATC Project No. 199CAR1808 14 Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision Compacted fill should be placed in lifts of 8 inches or less loose measure. In confined areas such as utility trenches, portable compaction equipment and thin lifts of 3 to 4 inches may be required to achieve specified degrees of compaction. We recommend that structural fill be compacted to at least 95 percent of the Standard Proctor (ASTM D-698) maximum dry density. The upper 12 inches beneath slabs and pavements should be compacted to at least 98 percent of the same criteria. Moisture content of the fill at the time of compaction should be maintained within a range of +\- 3% of the optimum moisture as determined by the Proctor test. In excavated areas, the upper 12 inches of soils intended to support pavements should be scarified and recompacted to at least 98 percent of the Standard Proctor maximum dry density. All fill material should be placed in horizontal lifts and adequately keyed into stripped and scarified subgrade soils. All new fills should also be benched into any existing slopes. During fill placement, an ATC soils technician should determine the degree of compaction and compliance with the project specifications by performing field density tests. At least one field density test should be made per 5,000 square feet of pavement area for each one -foot thickness of compacted soil. The testing frequency should be increased in confined areas. Any areas that do not meet the compaction specifications for density and moisture should be reworked to achieve compliance. The suitability of the on -site soils for reuse as structural fill must be confirmed by careful visual examination by the Geotechnical Engineer and/or his authorized representative and by the results of laboratory tests performed on proposed soil samples. We recommend that all materials be placed and compacted using the following criteria: • Soil fill should be placed in lifts of uniform thickness. The lift thickness should not exceed that which can be properly compacted throughout its entire depth with the equipment available, usually not more than 8 inches for clay soils and not more than 10 inches for granular soils for area fills. In confined areas such as utility trenches where only small and light compaction equipment can be used, lifts of 3 to 4 inches may be required to achieve the specified degree of compaction. • All fill should be properly keyed into stripped and scarified subgrades. The upper 1 foot of materials in planned cut areas or in areas which do not receive more than one foot of new fill should be scarified and recompacted using the guidelines outlined in this report section. • Fill should not be placed on frozen or saturated subgrades. • Fills should be placed and compacted to at least 95 percent of the Standard Proctor maximum dry density (ASTM Method D-698). Fills placed within 12 inches of slab or pavement levels should be placed and compacted to at least 95 percent of Standard Proctor maximum dry density. • A minimum of at least 2 tests per lift is recommended in the planned building area. For utility trenches, density tests should be taken every 50 linear feet for each fill layer placed. Any areas not meeting the compaction specifications should be recompacted to achieve compliance. ATC Project No. 199CAR1808 15 Report of Geotechnical Exploration Lindsay Meadows Subdivision July 3, 2017 • The soils should be placed within 3 percent of the optimum moisture content as determined by the Standard Proctor test. Aeration is often necessary to bring fill materials to the required moisture condition during wet and rainy periods. During dry periods, water may need to be added to bring the soils, especially granular soils, up to the proper moisture content to achieve proper compaction. Clay soils may require aeration prior to compaction even during dry periods. • Compacted fills should extend horizontally outside of planned paved areas at least 5 feet before sloping. • Temporary slopes should be regularly evaluated for indications of movements during the construction. 4.2 Wet Weather Construction Site grading that occurs during traditional wet weather periods will be problematic at this site. Extensive undercutting of saturated soils and chemical drying may be required if unfavorable weather conditions occur during fill placement operations at the site. Although specific recommendations would be made at the time of construction, the following guidelines are provided. • Saturated surface soils are difficult to dry by mechanical and/or chemical methods depending on the season and the soil type. Consequently, consideration should be given to removal and wasting of saturated surface soils at the site. • Lime or cement can be an effective in drying of soils that are typically about 4 to 8 percent wet of their optimum moisture content. We expect chemical drying will be required during periods of wet weather construction. • The on -site soils are sensitive to excessive moisture. These soils types may require undercutting and chemical drying if subjected to inclement weather conditions. • Disturbed or uncompacted soils will more readily absorb and hold water. Disturbed or uncompacted soils should be kept to a minimum area. Special attention and detail should be given to "sealing -off" or compaction with a sooth drummed roller of disturbed areas prior to wet weather periods. The contractor should also provide cut ditches to channel surface water runoff from the construction areas. The site should also be graded to prevent ponding of water on the site. Pumping should be performed in a timely manner in areas where water has collected. ATC Project No. 199CAR1808 16 Report of Geotechnical Exploration Lindsay Meadows Subdivision 4.3 Rock Excavation July 3, 2017 The site grading plan was not reviewed as part of this investigation. Assuming significant cuts are not planned for the site, we anticipate rock excavations will be required based on the borings performed. In addition, for "deeper" utility or stormwater excavations planned for the site, some rock materials may be encountered. ATC should review site grading plans prior to the site bidding to perform an additional evaluation of the anticipated site conditions and the potential for encountering rock. If rock is encountered, difficult excavation criteria are discussed below for your reference. In mass excavations for general site work, dense soils and partially weathered rock can usually be removed by ripping with a single -tooth ripper attached to a large crawler tractor or by breaking it out with a large front-end loader. In confined excavations such as foundations, utility trenches, removal of partially weathered rock typically requires use of large backhoes, pneumatic spades, or light blasting. Excavated rock and partially weathered rock is generally unsuitable for use as structural fill. The definition of rock can be a source of conflict during construction. The following definitions have been incorporated into specifications on other projects and are provided for your general guidance: General Excavation Rip Rock - Any material that cannot be removed by scrapers, loaders, pans, bulldozers, or graders; and requires the use of a single -tooth ripper mounted on a crawler tractor having a minimum draw bar pull rated at not less than 56,000 pounds (Caterpillar D-8T or equivalent). Blast Rock - Any material which cannot be excavated with a single -tooth ripper mounted on a crawler tractor having a minimum draw bar pull rated at not less than 56,000 pounds (Caterpillar D-8T or equivalent) or by a Caterpillar 977 front-end loader or equivalent; and occupying an original volume of at least one (1) cubic yard. Trench Excavation Blast Rock - Any material which cannot be excavated with a backhoe having a bucket curling force rated at not less than 25,700 pounds (Caterpillar Model 320D or equivalent) and occupying an original volume of at least one-half (1/2) cubic yard. ATC Project No. 199CAR1808 17 Report of Geotechnical Exploration July 3, 2017 Lindsay Meadows Subdivision 5.0 CONSTRUCTION CONSIDERATIONS If encountered, groundwater should be maintained at least about 3 feet below the final bottom of footing subgrade for the final subgrade observations and during placement of the foundation concrete. Should significant groundwater be encountered during construction, the geotechnical engineer should be contacted immediately to determine its effect on the design of the foundation. Where reinforcing steel is to be placed in the foundation, observations should be provided to ascertain that proper chairs or supports are provided and the reinforcing is properly positioned. Field observations and testing should also be provided for the earthwork construction for this project. As applicable, appropriate laboratory tests should be conducted on samples of the compacted backfill material, and field density tests should be conducted during the earthwork construction to ascertain that fill material and compaction requirements are being satisfied. Field observations and testing should also be provided by our field engineer and/or technician personnel under supervision of our geotechnical engineer assigned to this project. We cannot be responsible for the interpretation or implementation, by others, of recommendations given herein. Before beginning construction, the owner and contractor should become familiar with applicable local, state, and federal regulations, including the current OSHA Excavation and Trench Safety Standards. Construction site safety generally is the sole responsibility of the contractor, who should also be solely responsible for the means, methods, and sequencing of construction operations. We are providing this information solely as a service to our clients. Under no circumstances should the information provided herein be interpreted to mean that ATC Associates is assuming responsibility for construction site safety or the contractor's activities. This responsibility is not being implied and should not be inferred. ATC Project No. 199CAR1808 18 Report of Geotechnical Exploration Lindsay Meadows Subdivision 6.0 GENERAL AND LIMITATIONS July 3, 2017 Recommendations contained in this report are based on data obtained from the test boring performed at the locations shown on the Boring Location Plan in the Appendix. This report does not reflect any variations, which may occur beyond the test boring. This report has been prepared for the exclusive use of American Homes 4 Rent, to aid in the evaluation of this site and to assist their office and other design professionals in the design of this project. It is intended for use with regard to the specific project described herein. Any substantial changes in the design loading, site grading and estimated foundation depths, or location of the proposed structure, should be brought to our attention so that we may determine any effect on our recommendations given herein. This report should be made available to bidders prior to submitting their proposals and to the successful contractor and subcontractors for their information only, and to supply them with information relative to the subsurface investigation, and laboratory tests, etc. The opinions and conclusions expressed in this report are those of the geotechnical engineer and represent his interpretation of the subsurface conditions based on tests and results of analysis and studies he has conducted for design. This report has been prepared in accordance with generally accepted principles of geotechnical engineering practice and no other warranties are included, either expressed or implied, as to the professional services provided under the terms of our agreement. ATC Project No. 199CAR1808 19 Report of Geotechnical Exploration Brookhaven Subdivision November 8 2016 APPENDIX Important Information About Your Geotechnical Report Test Boring Location Plan Soil Test Boring Logs Reference Notes for Boring Logs ATC Project No. 199CAR1612 20