Geotechnical Engineering Report

Transcription

1 Geotechnical Engineering Report Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Project No Revised Prepared for: Gunn Memorial Public Library Yanceyville, North Carolina Prepared by: Terracon Consultants, Inc. Greensboro, North Carolina

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3 TABLE OF CONTENTS PAGE EXECUTIVE SUMMARY... i 1.0 INTRODUCTION PROJECT INFORMATION Project Description Site Location and Description SUBSURFACE CONDITIONS Site Geology Typical Profile Groundwater RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION Geotechnical Considerations Earthwork Site Preparation Material Types Compaction Requirements Utility Trench Backfill Grading and Drainage Earthwork Construction Considerations Foundation Recommendations Foundation Design Recommendations Seismic Considerations Floor Slabs Design Recommendations Floor Slab Construction Considerations Pavements Subgrade Preparation Design Considerations Estimates of Minimum Pavement Thickness Pavement Drainage Pavement Maintenance GENERAL COMMENTS...12 APPENDIX A FIELD EXPLORATION Exhibit A-1 Site Location Plan Exhibit A-2 Boring Location Plan Exhibit A-3 Field Exploration / Laboratory Description Exhibits A-4 to A-11 Boring Logs APPENDIX B LABORATORY TESTING Exhibit B-1 Atterberg Limits APPENDIX C SUPPORTING DOCUMENTS Exhibit C-1 General Notes Exhibit C-2 Unified Soil Classification Responsive Resourceful Reliable

4 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No EXECUTIVE SUMMARY Terracon has completed the geotechnical engineering report for the Caswell County Public Library project to be located in Yanceyville, North Carolina. Seven (7) soil test borings were performed in the area of the proposed building and pavement areas. Based on the information obtained from our subsurface exploration, the following geotechnical considerations were identified: Existing fill soils were encountered in borings B-3, B-3-A, and B-7 to depths ranging from 1.5 to 3 feet below the existing surface. The fill consists of medium stiff fat clay and loose silty sand. The majority of the fill appears to be placed in an uncontrolled manner. Isolated areas of more compressible material may be present at other locations and may require removal and replacement. Based on the encountered subsurface conditions throughout the site, we do not believe the refusal material in borings B-3 to be bedrock. The refusal in B-3 is likely debris or a utility. We recommend performing test pits, before construction or at the start of construction, in the vicinity of borings B-3 to determine the cause of the refusal. Based on our site visit and information pertaining to the site, settlement related distress was not observed in the existing building in the area of the proposed development. There is an inherent risk of structure settlement from compressible fill or unsuitable material within or buried by the fill that may not be discovered. This risk of unforeseen conditions cannot be eliminated without completely removing the existing fill within the building pad, parking and driveway areas. These risks can be reduced by performing adequate testing and evaluation during construction. This evaluation should begin with proofrolling areas at grade or to be filled upon. Care should be taken during any excavation adjacent the existing building to not undermine foundations for the existing building. If excavation is required in the area of existing footings, recommendations for underpinning can be provided if needed. Groundwater and difficult excavations are not anticipated to impact grading operations. Most of the near surface soils are fat clays (plastic soils). After grading, some plastic soils may be encountered at proposed bearing elevations for buildings, at floor slab subgrade elevations and at roadway subgrades. Treatment of foundation and slabs bearing in the clayey material is discussed herein. A net allowable bearing pressure of up to 2,000 pounds per square foot can be used for building foundation design. Responsive Resourceful Reliable i

5 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No We anticipate that unstable plastic soils may be present at or near planned pavement subgrade elevations. We recommend earthwork be performed during the summer to possibly reduce the instability of these subgrade plastic soils. Considering such, we recommend that contingencies be placed in the project budget for additional ABC stone (6 to 12 inches) and geogrid (BX-1100) for at least 50 percent of the pavement areas. At the time of constructions, the determination can be made as to what areas, if any, will require stabilization. The geotechnical engineer should be retained during the construction phase of the project to observe earthwork and to perform necessary tests and observations during subgrade preparation; proofrolling; placement and compaction of controlled compacted fills; backfilling of excavations into the completed subgrade, and just prior to construction of foundations. This summary should be used in conjunction with the entire report for design purposes. It should be recognized that details were not included or fully developed in this section, and the report must be read in its entirety for a comprehensive understanding of the items contained herein. The section titled GENERAL COMMENTS should be read for an understanding of the report limitations. Responsive Resourceful Reliable ii

6 GEOTECHNICAL ENGINEERING REPORT CASWELL COUNTY PUBLIC LIBRARY YANCEYVILLE, NORTH CAROLINA Terracon Project No June 15, INTRODUCTION Terracon has completed the geotechnical engineering report for the proposed Caswell County Public Library project to be located in Yanceyville, North Carolina. Seven (7) soil test borings were performed across the site. The purpose of these services is to provide information and geotechnical engineering recommendations relative to: subsurface soil conditions foundation design and construction groundwater conditions pavements site preparation / earthwork floor slab design and construction 2.0 PROJECT INFORMATION 2.1 Project Description ITEM Proposed construction Finished floor elevation (assumed) Grading DESCRIPTION The proposed project consists of renovation of existing library facility and new construction of a single-story library addition, approximately 7,582 square feet in area and constructed using steel framing composed of metal studs and brick veneer with a slab-on-grade floor. We anticipate that column, wall, and floor loads will be less than 150 kips per column, 3 kips per linear foot and 300 pounds per square foot, respectively. Unknown. We anticipate maximum cut and fill depths of less than 3 feet. 2.2 Site Location and Description ITEM Location Existing improvements Current ground cover Existing topography DESCRIPTION, Yanceyville, North Carolina. Existing single-story building with asphalt driveway and parking lots. Asphalt pavement and grass. Based on google maps aerial the site appears to be relatively flat. Responsive Resourceful Reliable 1

7 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No If any of the project information outlined above is inconsistent with the proposed construction, or if the design changes, Terracon requests the opportunity to review our recommendations. 3.0 SUBSURFACE CONDITIONS 3.1 Site Geology Piedmont Geology: The project site is located in the Piedmont Physiographic Province, an area underlain by ancient igneous and metamorphic rocks. The residual soils in this area are the product of in-place chemical weathering of rock. The typical residual soil profile consists of clayey soils near the surface where soil weathering is more advanced, underlain by sandy silts / silty sands that generally become harder / denser with depth to the top of parent bedrock. In residual materials the transition from soil to rock occurs gradually over a vertical distance ranging from a few feet to tens of feet. This transitional zone is termed partially weathered rock which is defined for engineering purposes as residual material that can be drilled with soil drilling methods and exhibits standard penetration test values in excess of 100 blows per foot. According to the 1985 Geologic Map of North Carolina, the bedrock under the site is Granitic Rock from the Permian/Pennsylvanian period. 3.2 Typical Profile Based on the results of the borings, subsurface conditions on the project site can be generalized as follows: Approximately 6 to 8 inches of asphalt pavement was encountered in borings B-1 through B-6. Underlying the asphalt pavement, approximately 4 to 7 inches of aggregate base course (ABC stone) was encountered. Approximately up to 4 to 5 inches of topsoil was encountered in borings B-5 and B-6. Beneath the surficial material, existing fill and residual material was encountered in each boring. Existing fill soils were encountered in borings B-3, B-3-A, and B-7 to depths ranging from 1.5 to 3 feet below the existing surface. The fill consists of medium stiff fat clay and loose silty sand. The majority of the fill appears to be placed in an uncontrolled manner. Isolated areas of more compressible material may be present at other locations and may require removal and replacement. In boring B-3, an unknown object or material caused auger refusal. The residual material at the site generally consists of zones of fat clay (CH), lean clay (CL), elastic silts (MH), sandy silts (ML), clayey sands (SC) and silty sands (SM). Most of the surface clays are moderately to highly plastic. The silts and clays were soft to stiff and sands were loose to very dense. Responsive Resourceful Reliable 2

8 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No Partially weathered rock was encountered in borings B-4 and B-5 at depths ranging from 8 to 18 feet below existing ground surface. Auger refusal materials, which we interpret to likely represent the top of rock were encountered in borings B-4 and B-5 at depths ranging from 9.7 to 19.5 feet below existing ground surface. For a detailed description of the conditions encountered in the borings, refer to the boring logs in Appendix A of this report. Stratification boundaries on the boring logs represent the approximate location of changes in soil types; in-situ, the transition between materials may be gradual. 3.3 Groundwater The boreholes were observed for the presence and level of groundwater while drilling and after the short period they were allowed to remain open. Groundwater was not observed in the borings at the time of observation. Groundwater level fluctuations can occur due to seasonal variations in the amount of rainfall, runoff and other factors not evident at the time the borings were performed. Therefore, groundwater levels during construction or at other times in the life of the structure may be higher or lower than the levels indicated on the boring logs. We do not expect the groundwater level to have a significant effect on the design and construction of the project, except possibly near the drainage feature for construction of the retaining wall. 4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION 4.1 Geotechnical Considerations Existing fill soils were encountered in borings B-3, B-3-A, and B-7 to depths ranging from 1.5 to 3 feet below the existing surface. The fill consists of medium stiff fat clay and loose silty sand. The majority of the fill appears to be placed in an uncontrolled manner. Isolated areas of more compressible material may be present at other locations and may require removal and replacement. Based on the encountered subsurface conditions throughout the site, we do not believe the refusal material in borings B-3 to be bedrock. The refusal in B-3 is likely debris or a utility. We recommend performing test pits, before construction or at the start of construction, in the vicinity of borings B-3 to determine the cause of the refusal. This risk of unforeseen conditions cannot be eliminated without completely removing the existing fill within the building pad, parking and driveway areas. These risks can be reduced by performing adequate testing and evaluation during construction. This evaluation should begin with proofrolling areas at grade or to be filled upon. Care should be taken during any excavation adjacent the existing building to not undermine foundations for the existing building. If excavation is required in the area of existing footings, recommendations for underpinning can be provided if needed. Responsive Resourceful Reliable 3

9 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No Most of the near surface soils are fat clays (plastic soils). After grading, some plastic soils may be encountered at proposed bearing elevations for buildings, at floor slab subgrade elevations and at roadway subgrades. Treatment of foundation and slabs bearing in the clayey material is discussed herein. We anticipate that unstable plastic soils may be present at or near planned pavement subgrade elevations. We recommend earthwork be performed during the summer to possibly reduce the instability of these subgrade plastic soils. Considering such, we recommend that contingencies be placed in the project budget for additional ABC stone (6 to 12 inches) and geogrid (BX-1100) for at least 50 percent of the pavement areas. At the time of constructions, the determination can be made as to what areas, if any, will require stabilization. The geotechnical engineer should be retained during the construction phase of the project to observe earthwork and to perform necessary tests and observations during subgrade preparation; proofrolling; placement and compaction of controlled compacted fills; backfilling of excavations into the completed subgrade, and just prior to construction of foundations. 4.2 Earthwork Site Preparation Based on our laboratory testing and soil classification, the current natural moisture content of the on-site, near-surface soil is near the soil s plastic limit. When the moisture content of soil reaches or exceeds its plastic limit, instability of the soil subgrade can be expected, especially under construction traffic. To help minimize soil disturbance and undercut potential, we recommend that positive site drainage be insisted upon during the project. The use of trucked equipment, in lieu of rubber tired vehicles, should also be considered. Site preparation should begin by removing the existing trees, undergrowth, and existing asphalt from the site. After the existing vegetation is removed, the site should be grubbed and the topsoil stripped and stockpiled for use in revegetating landscape areas or disposed of off-site. Based on the borings, we expect 3 to 4 inches of topsoil and 3 to 3.5 inches of asphalt will require removal. Existing aggregate base course material may be left in place, if desired, to help protect the site subgrades during the site preparation activities. Actual stripping depths may vary and should be evaluated by a Terracon representative at the time of construction. After the materials are removed, the subgrade soils should be evaluated visually for plasticity. High plasticity soils are not desirable at or near subgrades because of their potential to shrink and swell due to changes in moisture content. These soils may be used as fill in non-structural areas provided they are not placed within 1.5 feet of pavement subgrade and can be properly compacted. If existing highly plastic, CH and MH soils are present at building subgrade elevation, these should be undercut at least 12 inches and replaced with low to non-plastic soil material. Responsive Resourceful Reliable 4

10 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No After site stripping and plasticity evaluation, we recommend proofrolling in areas to receive fill or at the subgrade elevation to detect soft or loose soils. Proofrolling should be performed with a loaded, tandem-axle dump truck or similar rubber-tired construction equipment with a minimum gross weight of 20 tons. A representative of the geotechnical engineer should observe the proofrolling to identify areas of unstable or unsuitable subgrades. Proofrolling operations should be performed after a suitable period of dry weather to avoid degrading an otherwise acceptable subgrade Material Types Engineered fill should meet the following material property requirements: Fill Type 1 USCS Classification Acceptable Location for Placement Imported Low- to Moderate- Plasticity Soil Sand / Gravel with less than 15% fines (silt and clay) On-site soils On-site soils CL, ML, SC or SM GW/GP, SW/SP 2 SM, ML, SC, CL CH, MH All locations and elevations. NCDOT CABC (crushed aggregate base course) may be used beneath pavements. 2 NCDOT No. 57 (washed, crushed stone) may be used as a capillary break beneath floor slabs. 2 Generally suitable when placed at appropriate moisture content. Use at depths greater than 3 feet from planned building finished grades. 1. Controlled, compacted fill should consist of approved materials that are free of organic matter and debris. A sample of each material type should be submitted to the geotechnical engineer for evaluation. 2. Clean sand (less than 15% silt and clay) should not be used as general site fill in building and pavement areas to reduce risk of perched water developing in the surface fill as water infiltrating the sand fill becomes trapped above the less permeable clay located near the ground surface Compaction Requirements Item Fill Lift Thickness Compaction Requirements 1 Moisture Content Description 9-inches or less in loose thickness (4 to 6 lifts when handoperated equipment is used) Minimum of 95% of the materials standard Proctor maximum dry density (ASTM D698) Within the range of -3% to +3% of optimum moisture content as determined by the standard Proctor test at the time of placement and compaction 1. Engineered fill should be tested for moisture content and compaction during placement. If in-place density tests indicate the specified moisture or compaction limits have not been met, the area represented by the tests should be reworked and retested as required until the specified moisture and compaction requirements are achieved. Responsive Resourceful Reliable 5

11 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No Utility Trench Backfill All trench excavations should be made with sufficient working space to permit construction including backfill placement and compaction. If utility trenches are backfilled with relatively clean granular material, they should be capped with at least 18 inches of cohesive fill in non-pavement areas to reduce the infiltration and conveyance of surface water through the trench backfill. Utility trenches are a common source of water infiltration and migration. All utility trenches that penetrate beneath the building should be effectively sealed to restrict water intrusion and flow through the trenches that could migrate below the building. We recommend constructing an effective clay trench plug that extends at least 5 feet out from the face of the building exterior. The plug material should consist of clay compacted at a water content at or above the soils optimum water content. The clay fill should be placed to completely surround the utility line and be compacted in accordance with recommendations in this report. Some of the on-site soils encountered in utility trenches will likely include fat clays that will generally not be suitable for trench backfill in structural areas. If the fat clays are to be used in nonstructural areas, these soils will likely require drying Grading and Drainage During construction, grades should be sloped to promote runoff away from the construction area. Final grades should be sloped away from the structure on all sides to prevent ponding of water. If gutters / downspouts do not discharge directly onto pavement, they should not discharge directly adjacent to the building in landscaped areas. This can be accomplished through the use of splash-blocks, downspout extensions, and flexible pipes that are designed to attach to the end of the downspout if necessary. Flexible pipe should only be used if it is daylighted in such a manner that it gravity-drains collected water. Splash-blocks should also be considered below hose bibs and water spigots. Paved surfaces which adjoin the building should be sealed with caulking or other sealant to prevent moisture infiltration at the building envelope; maintenance should be performed as necessary to maintain the seal Earthwork Construction Considerations Although the exposed subgrade is anticipated to be relatively stable upon initial exposure, unstable subgrade conditions could develop during general construction operations, particularly if the soils are wetted and/or subjected to repetitive construction traffic. The use of light construction equipment would aid in reducing subgrade disturbance. Should unstable subgrade conditions develop, stabilization measures will need to be employed. Upon completion of filling and grading, care should be taken to maintain the subgrade moisture content prior to construction of floor slabs and pavements. Construction traffic over the completed subgrade should be avoided to the extent practical. The site should also be graded to prevent ponding of surface water on the prepared subgrades or in excavations. If the Responsive Resourceful Reliable 6

12 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No subgrade should become frozen, desiccated, saturated, or disturbed, the affected material should be removed or these materials should be scarified, moisture conditioned, and recompacted prior to floor slab and pavement construction. All temporary excavations should be sloped or braced as required by Occupational Health and Safety Administration (OSHA) regulations to provide stability and safe working conditions. The geotechnical engineer should be retained during the construction phase of the project to observe earthwork and to perform necessary tests and observations during subgrade preparation; proof-rolling; placement and compaction of controlled compacted fills; backfilling of excavations into the completed subgrade, and just prior to construction of building floor slabs. 4.3 Foundation Recommendations In our opinion, the proposed building can be supported by a shallow, spread footing foundation system consisting of shallow foundations bearing on residual soil, approved existing fill or new controlled fill. Design recommendations for foundation systems are presented in the following table and paragraphs Foundation Design Recommendations Description Net allowable bearing pressure 1 Minimum embedment below lowest adjacent finished grade 2 Approximate total settlement 3 Estimated differential settlement 3 Value 2,000 psf 18 inches Less than 1 inch Less than 3/4 inch over 40 feet 1. The recommended net allowable bearing pressure is the pressure in excess of the minimum surrounding overburden pressure at the footing base elevation. 2. In areas of plastic soil, the footing excavations should be extended to a depth of at least 3 feet below finished grades and backfilled with non-plastic material. 3. The actual magnitude of settlement that will occur beneath the foundation slab depends upon the variations within the subsurface soil profile, the structural loading conditions and the quality of the foundation excavation. The estimated total and differential settlements listed assume that the foundation related earthwork and the foundation design are completed in accordance with our recommendations. Due to the plastic surface soils, we recommend the perimeter foundations be extended to a depth of at least 3 feet below finished grades and backfilled with non-plastic material. A representative of the geotechnical engineer should be retained at the time of foundation construction to examine the bearing conditions in the foundation excavations. A combination of hand auger borings, dynamic cone penetrometer (DCP) testing, and probing should be performed as appropriate to confirm the suitability of the foundation bearing materials for the Responsive Resourceful Reliable 7

13 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No design bearing pressure. Soft, loose, or otherwise unsuitable materials should be overexcavated and replaced with compacted soil fill. The base of all foundation excavations should be free of water and loose soil prior to placing concrete. Concrete should be placed soon after excavating to reduce bearing soil disturbance. Should the soils at bearing level become excessively disturbed or saturated, the affected soil should be removed prior to placing concrete. 4.4 Seismic Considerations Code Used Site Classification 2005 ASCE 7 (ref IBC) C Ss = S1 = Fa = 1.2 Fv = 1.7 SDS = SD1 = Floor Slabs Design Recommendations Item Floor slab support Modulus of subgrade reaction (k) Stone Base Course 1 Description Approved/prepared site soils or new engineered fill 100 pounds per square inch per inch (psi/in) for point loading conditions. At least 4 inches of crushed stone (NCDOT CABC or No. 57) 1. The floor slab design should include a capillary break, comprised of free-draining, compacted, granular material, at least 4 inches thick and can be considered as part of the low volume change zone. Free-draining granular material should have less than 5 percent fines (material passing the #200 sieve). Other design considerations such as cold temperatures and condensation development could warrant more extensive design provisions. For the floor slabs partially bearing on highly plastic soils, we recommend that the soils be undercut at least 12 inches and replaced with low to non-plastic material or stone Floor Slab Construction Considerations On most project sites, the site grading is generally accomplished early in the construction phase. However as construction proceeds, the floor slab subgrade may be disturbed due to utility excavations, construction traffic, desiccation, rainfall, etc. As a result, the floor slab subgrade may not be suitable for placement of base rock and concrete and corrective action will be required. Responsive Resourceful Reliable 8

14 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No We recommend the area underlying the floor slab be rough graded and then thoroughly proofrolled with a loaded tandem axle dump truck prior to final grading and placement of base rock. Particular attention should be paid to high traffic areas that were rutted and disturbed earlier and to areas where backfilled trenches are located. Areas where unsuitable conditions are located should be repaired by removing and replacing the affected material with properly compacted fill. All floor slab subgrade areas should be moisture conditioned and properly compacted to the recommendations in this report immediately prior to placement of the base rock and concrete. 4.6 Pavements Subgrade Preparation On most project sites, the site grading is accomplished relatively early in the construction phase. Fills are placed and compacted in a uniform manner. However, as construction proceeds, excavations are made into these areas, rainfall and surface water saturates some areas, heavy traffic from concrete trucks and other delivery vehicles disturbs the subgrade and many surface irregularities are filled in with loose soils to improve trafficability temporarily. As a result, the pavement subgrades, initially prepared early in the project, should be carefully evaluated as the time for pavement construction approaches. We recommend the moisture content and density of the top 9 inches of the subgrade be evaluated and the pavement subgrades be proofrolled within two days prior to commencement of actual paving operations. Areas not in compliance with the required ranges of moisture or density should be moisture conditioned and recompacted. Particular attention should be paid to high traffic areas that were rutted and disturbed earlier and to areas where backfilled trenches are located. Areas where unsuitable conditions are located should be repaired by removing and replacing the materials with properly compacted fills. As previously stated, some of the near surface soils are highly plastic clays. It is not desirable to have these plastic soils at subgrade for pavements and the presence of these soils at subgrade would likely affect the pavement service life. When dry, these soils should proofroll successfully; however, over time, these soils may get wet due to infiltration through cracks in the pavement or water migration through the base course. We recommend that contingencies be placed in the project budget for additional ABC stone (6 to 12 inches) and geogrid (BX-1100) for at least 50 percent of the pavement areas. At the time of constructions, the determination can be made as to what areas, if any, will require stabilization. Responsive Resourceful Reliable 9

15 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No Utilizing geogrid can help extend the pavement service life if used in areas of high plasticity soils and unstable areas. If a significant precipitation event occurs after the evaluation or if the surface becomes disturbed, the subgrade should be reviewed by qualified personnel immediately prior to paving. The subgrade should be in its finished form at the time of the final review Design Considerations Traffic patterns and anticipated loading conditions were not available at the time that this report was prepared. However, we anticipate that traffic loads will be produced primarily by automobile, light truck traffic and a weekly dumpster truck visit. The thickness of pavements subjected to heavy truck traffic have not been considered. Expansive soils are present at this site. This report provides recommendations to help mitigate the effects of soil shrinkage and expansion. However, even if these recommendations are followed some pavement distress could still occur. It is, therefore, important to minimize moisture changes in the subgrade both during construction and during the life of the pavement to reduce shrink/swell movements. Pavement performance is affected by its surroundings. In addition to providing preventive maintenance, the civil engineer should consider the following recommendations in the design and layout of pavements: Final grade adjacent to parking lots and drives should slope down from pavement edges at a minimum 2%; The subgrade and the pavement surface should have a minimum ¼ inch per foot slope to promote proper surface drainage; Install pavement drainage surrounding areas anticipated for frequent wetting (e.g., garden centers, wash racks); Install joint sealant and seal cracks immediately; Seal all landscaped areas in, or adjacent to pavements to reduce moisture migration to subgrade soils; Place compacted, low permeability backfill against the exterior side of curb and gutter; and, Place curb, gutter and/or sidewalk directly on clay subgrade soils rather than on unbound granular base course materials. Responsive Resourceful Reliable 10

16 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No Estimates of Minimum Pavement Thickness Pavement Type Rigid Material Portland Cement Concrete (4,000 psi) Crushed Aggregate Base Course (NCDOT CABC Type 1 or Type 2) Layer Thickness (inches) Light Duty Heavy Duty Flexible (Superpave) Note: * - Placed in two, 1.5-inch lifts. Asphalt Surface (NCDOT SF-9.5A) Asphalt Binder (NCDOT I-19.0B) or (S9.5B) Crushed Aggregate Base Course (NCDOT CABC Type 1 or Type 2) 3* The placement of a partial pavement thickness for use during construction is not suggested without a detailed pavement analysis incorporating construction traffic. In addition, we should be contacted to confirm the traffic assumptions outlined above. If the actual traffic varies from the assumptions outlined above, modification of the pavement section thickness will be required. Recommendations for pavement construction presented depend upon compliance with recommended material specifications. To assess compliance, observation and testing should be performed under the direction of the geotechnical engineer. Asphalt concrete aggregates and base course materials should conform to the North Carolina Department of Transportation (NCDOT) "Standard Specifications for Roads and Structures. Concrete pavement should be air-entrained and have a minimum compressive strength of 4,000 psi after 28 days of laboratory curing per ASTM C-31. The performance of all pavements can be enhanced by minimizing excess moisture which can reach the subgrade soils. The following recommendations should be considered a minimum: site grading at a minimum 2 percent grade away from the pavements; subgrade and pavement surface with a minimum 1/4 inch per foot slope to promote proper surface drainage; and installation of joint sealant to seal cracks immediately. Seal all landscaped areas in, or adjacent to pavements to reduce moisture migration to subgrade soils; Place compacted, low permeability backfill against the exterior side of curb and gutter; and, Responsive Resourceful Reliable 11

17 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No Place curb, gutter and/or sidewalk directly on low permeability subgrade soils rather than on unbound granular base course materials Pavement Drainage Pavements should be sloped to provide rapid drainage of surface water. Water allowed to pond on or adjacent to the pavements could saturate the subgrade and contribute to premature pavement deterioration. In addition, the pavement subgrade should be graded to provide positive drainage within the granular base section. Appropriate sub-drainage or connection to a suitable daylight outlet should be provided to remove water from the granular subbase Pavement Maintenance The pavement sections provided in this report represent minimum recommended thicknesses and, as such, periodic maintenance should be anticipated. Therefore preventive maintenance should be planned and provided for through an on-going pavement management program. Maintenance activities are intended to slow the rate of pavement deterioration, and to preserve the pavement investment. Maintenance consists of both localized maintenance (e.g., crack and joint sealing and patching) and global maintenance (e.g., surface sealing). Preventive maintenance is usually the first priority when implementing a pavement maintenance program. Additional engineering observation is recommended to determine the type and extent of a cost effective program. Even with periodic maintenance, some movements and related cracking may still occur and repairs may be required. 5.0 GENERAL COMMENTS Terracon should be retained to review the final design plans and specifications so comments can be made regarding interpretation and implementation of our geotechnical recommendations in the design and specifications. Terracon also should be retained to provide observation and testing services during grading, excavation, foundation construction and other earth-related construction phases of the project. The analysis and recommendations presented in this report are based upon the data obtained from the borings performed at the indicated locations and from other information discussed in this report. This report does not reflect variations that may occur across the site, or due to the modifying effects of weather. The nature and extent of such variations may not become evident until during or after construction. If variations appear, we should be immediately notified so that further evaluation and supplemental recommendations can be provided. The scope of services for this project does not include either specifically or by implication any environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the potential for such contamination or pollution, other studies should be undertaken. Responsive Resourceful Reliable 12

18 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No This report has been prepared for the exclusive use of our client for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranties, either express or implied, are intended or made. Site safety, excavation support, and dewatering requirements are the responsibility of others. In the event that changes in the nature, design, or location of the project as outlined in this report are planned, the conclusions and recommendations contained in this report shall not be considered valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this report in writing. Responsive Resourceful Reliable 13

19 APPENDIX A FIELD EXPLORATION

20 SITE TOPOGRAPHIC MAP IMAGE COURTESY OF THE U.S. GEOLOGICAL SURVEY QUADRANGLES INCLUDE: YANCEYVILLE, NC (1/1/2002). DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES Project Manager: L. Akins Drawn by: L. Akins Checked by: L. Akins Approved by: J. Hoskins Project No Scale: 1 =2,000 File Name: Date: 5/23/ W Friendly Ave Ste G Greensboro, NC SITE LOCATION Caswell County Public Library Yanceyville, NC Exhibit A-1

21 AERIAL PHOTOGRAPHY PROVIDED BY MICROSOFT BING MAPS DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION PURPOSES Project Manager: L. Akins Drawn by: L. Akins Checked by: L. Akins Approved by: J. Hoskins Project No Scale: N.T.S. File Name: Date: 5/23/ W Friendly Ave Ste G Greensboro, NC EXPLORATION PLAN Caswell County Public Library Yanceyville, NC Exhibit A-2

22 Geotechnical Engineering Report - Revised Caswell County Public Library Yanceyville, North Carolina June 15, 2017 Terracon Project No Field Exploration The boring locations were established in the field by measuring from existing site features and estimating right angles. The locations of the borings should be considered accurate only to the degree implied by the means and methods used to define them. The borings were drilled by Mobile-57 truck-mounted drill rig equipped with hollow stem augers. Samples of the soil encountered in the borings were obtained using the split barrel sampling procedures. In the split-barrel sampling procedure, the number of blows required to advance a standard 2-inch O.D. split-barrel sampler the last 12 inches of the typical total 18-inch penetration by means of a 140-pound safety hammer with a free fall of 30 inches, is the standard penetration resistance value (SPT-N). This value is used to estimate the in-situ relative density of cohesionless soils and consistency of cohesive soils. Soil samples were taken at 2.5-foot intervals above a depth of 10 feet and at 5-foot intervals below 10 feet. The samples were tagged for identification, sealed to reduce moisture loss, and taken to our laboratory for further examination, testing, and classification. Information provided on the boring logs attached to this report includes soil descriptions, consistency evaluations, boring depths, sampling intervals, and groundwater conditions. The borings were backfilled with auger cuttings prior to the drill crew leaving the site. A field log of each boring was prepared by the drill crew. These logs included visual classifications of the materials encountered during drilling as well as the driller s interpretation of the subsurface conditions between samples. Final boring logs included with this report represent the engineer's interpretation of the field logs and include modifications based on laboratory observation of the samples. Descriptive classifications of the soils indicated on the boring logs are in accordance with the enclosed General Notes and the Unified Soil Classification System. Also shown are estimated Unified Soil Classification Symbols. A brief description of this classification system is attached to this report. Responsive Resourceful Reliable Exhibit A-3

23 PROJECT: Caswell County Public Library BORING LOG NO. B-1 Gunn Memorial Public Library CLIENT: Page 1 of 1 SITE: GRAPHIC LOG Yanceyville, NC LOCATION See Exhibit A-2 Latitude: Longitude: DEPTH TOPSOIL, 6" Topsoil 0.5 RESIDUAL - FAT CLAY (CH), with sand, tan brown, soft, wet Rhonda Griffin DEPTH (Ft.) WATER LEVEL OBSERVATIONS SAMPLE TYPE FIELD TEST RESULTS WATER CONTENT (%) ATTERBERG LIMITS LL-PL-PI THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL CASWELL COUNTY PU.GPJ TERRACON_DATATEMPLATE.GDT 6/8/ SILTY SAND (SM), trace mica, tan brown, medium dense, moist PARTIALLY WEATHERED ROCK - SILTY SAND (SM), with quartz fragments, tan white, moist 13.0 PARTIALLY WEATHERED ROCK - SILTY SAND (SM), tan brown, moist 14.8 Boring Terminated at 14.8 Feet Stratification lines are approximate. In-situ, the transition may be gradual. Advancement Method: Hollow Stem Auger Abandonment Method: WATER LEVEL OBSERVATIONS At completion of drilling: dry See Exhibit A-3 for description of field procedures. See Appendix B for description of laboratory procedures and additional data (if any). See Appendix C for explanation of symbols and abbreviations W Friendly Ave Ste G Greensboro, NC Hammer Type: Automatic Notes: 5 10 Boring Started: 5/22/2017 Drill Rig: Mobile B-57 Project No.: N= N= N=17 50/5" /3" 50/3" Boring Completed: 5/22/2017 Driller: M. Hartley Exhibit: A-4

24 PROJECT: Caswell County Public Library BORING LOG NO. B-2 Gunn Memorial Public Library CLIENT: Page 1 of 1 SITE: GRAPHIC LOG Yanceyville, NC LOCATION See Exhibit A-2 Latitude: Longitude: DEPTH TOPSOIL, 7" Topsoil 0.6 RESIDUAL - FAT CLAY (CH), with sand, tan brown, soft, wet Rhonda Griffin DEPTH (Ft.) WATER LEVEL OBSERVATIONS SAMPLE TYPE FIELD TEST RESULTS WATER CONTENT (%) ATTERBERG LIMITS LL-PL-PI THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL CASWELL COUNTY PU.GPJ TERRACON_DATATEMPLATE.GDT 6/8/ SILTY SAND (SM), with quartz fragments, tan brown, medium dense, moist PARTIALLY WEATHERED ROCK - SILTY SAND (SM), with quartz fragments, tan white, moist SILTY SAND (SM), tan, dense, moist PARTIALLY WEATHERED ROCK - SILTY SAND (SM), with quartz fragments, tan white, moist 14.7 Boring Terminated at 14.7 Feet Stratification lines are approximate. In-situ, the transition may be gradual. Advancement Method: Hollow Stem Auger Abandonment Method: WATER LEVEL OBSERVATIONS At completion of drilling: dry See Exhibit A-3 for description of field procedures. See Appendix B for description of laboratory procedures and additional data (if any). See Appendix C for explanation of symbols and abbreviations W Friendly Ave Ste G Greensboro, NC Hammer Type: Automatic Notes: 5 10 Boring Started: 5/22/2017 Drill Rig: Mobile B-57 Project No.: N= N= /1" 50/1" N= /2" 50/2" Boring Completed: 5/22/2017 Driller: M. Hartley Exhibit: A-5

25 PROJECT: Caswell County Public Library BORING LOG NO. B-3 Gunn Memorial Public Library CLIENT: Page 1 of 1 THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL CASWELL COUNTY PU.GPJ TERRACON_DATATEMPLATE.GDT 6/8/17 SITE: GRAPHIC LOG DEPTH 0.3 ASPHALT, 3" Asphalt 0.7 AGGREGATE BASE COURSE, 5" ABC Stone FILL - SILTY SAND (SM), trace clay and concrete fragments, dark gray, wet to moist 1.8 Yanceyville, NC LOCATION See Exhibit A-2 Latitude: Longitude: Auger Refusal at 1.8 Feet Stratification lines are approximate. In-situ, the transition may be gradual. Advancement Method: Hollow Stem Auger Abandonment Method: WATER LEVEL OBSERVATIONS At completion of drilling: dry Rhonda Griffin See Exhibit A-3 for description of field procedures. See Appendix B for description of laboratory procedures and additional data (if any). See Appendix C for explanation of symbols and abbreviations W Friendly Ave Ste G Greensboro, NC Hammer Type: Automatic Notes: DEPTH (Ft.) WATER LEVEL OBSERVATIONS Boring Started: 5/22/2017 Drill Rig: Mobile B-57 Project No.: SAMPLE TYPE FIELD TEST RESULTS 3-50/3" 50/3" Boring Completed: 5/22/2017 Driller: M. Hartley Exhibit: WATER CONTENT (%) A-6 ATTERBERG LIMITS LL-PL-PI

26 PROJECT: Caswell County Public Library BORING LOG NO. B-3-A Gunn Memorial Public Library CLIENT: Page 1 of 1 THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL CASWELL COUNTY PU.GPJ TERRACON_DATATEMPLATE.GDT 6/8/17 SITE: GRAPHIC LOG DEPTH 0.3 ASPHALT, 3" Asphalt 0.7 AGGREGATE BASE COURSE, 5" ABC Stone FILL - SILTY SAND (SM), with clay, brown, loose, moist Yanceyville, NC LOCATION See Exhibit A-2 Latitude: Longitude: RESIDUAL - FAT CLAY (CH), trace sand, tan, medium stiff, moist SILTY SAND (SM), witth quartz fragments, tan white, medium dense, moist SANDY SILT (ML), tan brown, very stiff, moist 13.0 SILTY SAND (SM), tan, dense, moist 15.0 Boring Terminated at 15 Feet Stratification lines are approximate. In-situ, the transition may be gradual. Advancement Method: Hollow Stem Auger Abandonment Method: WATER LEVEL OBSERVATIONS At completion of drilling: dry Rhonda Griffin See Exhibit A-3 for description of field procedures. See Appendix B for description of laboratory procedures and additional data (if any). See Appendix C for explanation of symbols and abbreviations W Friendly Ave Ste G Greensboro, NC Hammer Type: Automatic Notes: DEPTH (Ft.) WATER LEVEL OBSERVATIONS Boring Started: 5/22/2017 Drill Rig: Mobile B-57 Project No.: SAMPLE TYPE FIELD TEST RESULTS N= N= N= N= N=32 Boring Completed: 5/22/2017 Driller: M. Hartley Exhibit: WATER CONTENT (%) A-7 ATTERBERG LIMITS LL-PL-PI

27 PROJECT: Caswell County Public Library BORING LOG NO. B-4 Gunn Memorial Public Library CLIENT: Page 1 of 1 THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL CASWELL COUNTY PU.GPJ TERRACON_DATATEMPLATE.GDT 6/8/17 SITE: GRAPHIC LOG DEPTH 0.3 ASPHALT, 3.5" Asphalt AGGREGATE BASE COURSE, 9" ABC Stone 1.0 RESIDUAL - CLAYEY SAND (SC), orange brown, loose, wet Yanceyville, NC LOCATION See Exhibit A-2 Latitude: Longitude: FAT CLAY (CH), with sand, tan orange, stiff, moist SILTY SAND (SM), with quartz fragments, tan, dense, moist PARTIALLY WEATHERED ROCK - SILTY SAND (SM), with quartz fragments, tan, moist Auger Refusal at 9.7 Feet Stratification lines are approximate. In-situ, the transition may be gradual. Advancement Method: Hollow Stem Auger Abandonment Method: WATER LEVEL OBSERVATIONS At completion of drilling: dry Rhonda Griffin See Exhibit A-3 for description of field procedures. See Appendix B for description of laboratory procedures and additional data (if any). See Appendix C for explanation of symbols and abbreviations W Friendly Ave Ste G Greensboro, NC Hammer Type: Automatic Notes: DEPTH (Ft.) 5 WATER LEVEL OBSERVATIONS Boring Started: 5/22/2017 Drill Rig: Mobile B-57 Project No.: SAMPLE TYPE FIELD TEST RESULTS N= N= N= /5" 50/5" 50/0" Boring Completed: 5/22/2017 Driller: M. Hartley Exhibit: WATER CONTENT (%) A-8 ATTERBERG LIMITS LL-PL-PI

28 PROJECT: Caswell County Public Library BORING LOG NO. B-5 Gunn Memorial Public Library CLIENT: Page 1 of 2 SITE: GRAPHIC LOG Yanceyville, NC LOCATION See Exhibit A-2 Latitude: Longitude: DEPTH 0.4 TOPSOIL, 5" Topsoil RESIDUAL - SANDY FAT CLAY (CH), tan orange, soft, wet Rhonda Griffin DEPTH (Ft.) WATER LEVEL OBSERVATIONS SAMPLE TYPE FIELD TEST RESULTS WATER CONTENT (%) ATTERBERG LIMITS LL-PL-PI THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL CASWELL COUNTY PU.GPJ TERRACON_DATATEMPLATE.GDT 6/8/ SILTY SAND (SM), tan brown, dense, moist SILTY SAND (SM), with quartz fragments, tan brown, medium dense to very dense, wet to moist Stratification lines are approximate. In-situ, the transition may be gradual. Advancement Method: Hollow Stem Auger Abandonment Method: WATER LEVEL OBSERVATIONS At completion of drilling: dry See Exhibit A-3 for description of field procedures. See Appendix B for description of laboratory procedures and additional data (if any). See Appendix C for explanation of symbols and abbreviations W Friendly Ave Ste G Greensboro, NC Hammer Type: Automatic Notes: Boring Started: 5/22/2017 Drill Rig: Mobile B-57 Project No.: N= N= N= N= N=85 Driller: M. Hartley Boring Completed: 5/22/2017 Exhibit: A-9

29 PROJECT: Caswell County Public Library BORING LOG NO. B-5 Gunn Memorial Public Library CLIENT: Page 2 of 2 THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL CASWELL COUNTY PU.GPJ TERRACON_DATATEMPLATE.GDT 6/8/17 SITE: GRAPHIC LOG DEPTH SILTY SAND (SM), with quartz fragments, tan brown, medium dense to very dense, wet to moist (continued) 18.0 Yanceyville, NC LOCATION See Exhibit A-2 Latitude: Longitude: PARTIALLY WEATHERED ROCK - SILTY SAND (SM), with rock fragments and mica, tan brown, moist 19.5 Auger Refusal at 19.5 Feet Stratification lines are approximate. In-situ, the transition may be gradual. Advancement Method: Hollow Stem Auger Abandonment Method: WATER LEVEL OBSERVATIONS At completion of drilling: dry Rhonda Griffin See Exhibit A-3 for description of field procedures. See Appendix B for description of laboratory procedures and additional data (if any). See Appendix C for explanation of symbols and abbreviations W Friendly Ave Ste G Greensboro, NC Hammer Type: Automatic Notes: DEPTH (Ft.) WATER LEVEL OBSERVATIONS Boring Started: 5/22/2017 Drill Rig: Mobile B-57 Project No.: SAMPLE TYPE FIELD TEST RESULTS 10-50/1" 50/1" Boring Completed: 5/22/2017 Driller: M. Hartley Exhibit: WATER CONTENT (%) A-9 ATTERBERG LIMITS LL-PL-PI

30 PROJECT: Caswell County Public Library BORING LOG NO. B-6 Gunn Memorial Public Library CLIENT: Page 1 of 1 SITE: GRAPHIC LOG Yanceyville, NC LOCATION See Exhibit A-2 Latitude: Longitude: DEPTH 0.3 TOPSOIL, 3" Topsoil RESIDUAL - LEAN CLAY (CL), with sand, tan orange, medium stiff, wet Rhonda Griffin DEPTH (Ft.) WATER LEVEL OBSERVATIONS SAMPLE TYPE FIELD TEST RESULTS WATER CONTENT (%) ATTERBERG LIMITS LL-PL-PI THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL CASWELL COUNTY PU.GPJ TERRACON_DATATEMPLATE.GDT 6/8/ SANDY SILT (ML), trace clay, orange brown, medium stiff, wet SILTY SAND (SM), tan orange, medium dense, moist 10.0 Boring Terminated at 10 Feet Stratification lines are approximate. In-situ, the transition may be gradual. Advancement Method: Hollow Stem Auger Abandonment Method: WATER LEVEL OBSERVATIONS At completion of drilling: dry See Exhibit A-3 for description of field procedures. See Appendix B for description of laboratory procedures and additional data (if any). See Appendix C for explanation of symbols and abbreviations W Friendly Ave Ste G Greensboro, NC 5 10 Hammer Type: Automatic Notes: Boring Started: 5/22/2017 Drill Rig: Mobile B-57 Project No.: N= N= N= N=10 Driller: M. Hartley Boring Completed: 5/22/2017 Exhibit: A-10

31 PROJECT: Caswell County Public Library BORING LOG NO. B-7 Gunn Memorial Public Library CLIENT: Page 1 of 1 SITE: GRAPHIC LOG Yanceyville, NC LOCATION See Exhibit A-2 Latitude: Longitude: DEPTH 0.3 TOPSOIL, 3" Topsoil FILL - FAT CLAY (CH), with sand, tan orange, medium stiff, wet Rhonda Griffin DEPTH (Ft.) WATER LEVEL OBSERVATIONS SAMPLE TYPE FIELD TEST RESULTS WATER CONTENT (%) ATTERBERG LIMITS LL-PL-PI THIS BORING LOG IS NOT VALID IF SEPARATED FROM ORIGINAL REPORT. GEO SMART LOG-NO WELL CASWELL COUNTY PU.GPJ TERRACON_DATATEMPLATE.GDT 6/8/ RESIDUAL - CLAYEY SAND (SC), orange brown, loose to medium dense, wet to moist ELASTIC SILT (MH), trace sand, red orange, stiff, moist 10.0 Boring Terminated at 10 Feet Stratification lines are approximate. In-situ, the transition may be gradual. Advancement Method: Hollow Stem Auger Abandonment Method: WATER LEVEL OBSERVATIONS At completion of drilling: dry See Exhibit A-3 for description of field procedures. See Appendix B for description of laboratory procedures and additional data (if any). See Appendix C for explanation of symbols and abbreviations W Friendly Ave Ste G Greensboro, NC 5 10 Hammer Type: Automatic Notes: Boring Started: 5/22/2017 Drill Rig: Mobile B-57 Project No.: N= N= N= N=10 Boring Completed: 5/22/2017 Driller: M. Hartley Exhibit: A-11

32 APPENDIX B LABORATORY TESTING

33 ATTERBERG LIMITS RESULTS ASTM D LABORATORY TESTS ARE NOT VALID IF SEPARATED FROM ORIGINAL REPORT. ATTERBERG LIMITS CASWELL COUNTY PU.GPJ TERRACON_DATATEMPLATE.GDT 6/2/17 P L A S T I C I T Y I N D E X "U" Line CL or OL CH or OH "A" Line MH or OH CL-ML ML or OL LIQUID LIMIT Boring ID Depth LL PL PI Fines USCS Description B-5 B PROJECT: Caswell County Public Library SITE: Yanceyville, NC CH CL 7327 W Friendly Ave Ste G Greensboro, NC SANDY FAT CLAY LEAN CLAY with SAND PROJECT NUMBER: CLIENT: Gunn Memorial Public Library EXHIBIT: B-1

34 APPENDIX C SUPPORTING DOCUMENTS

35

36 UNIFIED SOIL CLASSIFICATION SYSTEM Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests A Coarse Grained Soils: More than 50% retained on No. 200 sieve Fine-Grained Soils: 50% or more passes the No. 200 sieve Gravels: More than 50% of coarse fraction retained on No. 4 sieve Sands: 50% or more of coarse fraction passes No. 4 sieve Silts and Clays: Liquid limit less than 50 Silts and Clays: Liquid limit 50 or more Group Symbol Soil Classification Group Name B Clean Gravels: Cu 4 and 1 Cc 3 E GW Well-graded gravel F Less than 5% fines C Cu 4 and/or 1 Cc 3 E GP Poorly graded gravel F Gravels with Fines: Fines classify as ML or MH GM Silty gravel F,G,H More than 12% fines C Fines classify as CL or CH GC Clayey gravel F,G,H Clean Sands: Cu 6 and 1 Cc 3 E SW Well-graded sand I Less than 5% fines D Cu 6 and/or 1 Cc 3 E SP Poorly graded sand I Sands with Fines: Fines classify as ML or MH SM Silty sand G,H,I More than 12% fines D Fines classify as CL or CH SC Clayey sand G,H,I Inorganic: Organic: Inorganic: Organic: PI PI Liquid limit - oven dried Liquid limit - not dried Liquid limit - oven dried Liquid limit - not dried J J CL ML 0.75 OL CH MH 0.75 OH Highly organic soils: Primarily organic matter, dark in color, and organic odor PT Peat Lean clay K,L,M Silt K,L,M Organic clay K,L,M,N Organic silt K,L,M,O Fat clay K,L,M Elastic Silt K,L,M Organic clay K,L,M,P Organic silt K,L,M,Q A Based on the material passing the 3-inch (75-mm) sieve B If field sample C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorly graded gravel with silt, GP-GC poorly graded gravel with clay. D Sands with 5 to 12% fines require dual symbols: SW-SM well-graded sand with silt, SW-SC well-graded sand with clay, SP-SM poorly graded sand with silt, SP-SC poorly graded sand with clay E Cu = D 60/D 10 Cc = D (D ) 2 x D 60 F If soil contains G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM. H I If soil contains J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay. K whichever is predominant. L If soil contains group name. M If soil contains 30% plus No. 200, predominantly gravel, add N PI O PI P PI plots on or above Q Exhibit C-2