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HomeMy WebLinkAboutHARMONY RIDGE PUD - Filed SER-SUBSURFACE EXPLORATION REPORTSUBSURFACE EXPLORATION REPORT HARMONY RIDGE P.U.D. FORT COLLINS, COLORADO EEC PROJECT NO. 1972027 2J EARTH ENGINEERING CONSULTANTS, INC. EEC EARTH ENGINEERING CONSULTANTS, INC. May 5, 1997 Positive Environments, Inc. P.O. Box 98 Fort Collins, Colorado 80522 Attn: Mr. Joe Vansant Re: Subsurface Exploration Report Harmony Ridge P.U.D. Fort Collins, Colorado EEC Project No. 1972027 Mr. Vansant: Enclosed, herewith, are the results of the subsurface exploration you requested for the referenced project. In summary, the subsurface materials encountered in the on -site borings consisted of granular and essentially granular soils overlying weathered claystone bedrock. The depth to the bedrock was generally on the order of 10 feet or greater; however, was encountered as shallow as 5'/2 feet in one boring. Based on the materials observed at the test boring locations, it is our opinion that most of the proposed residential structures could be supported on conventional footing foundations bearing in the natural granular and essentially granular soils. Care will be necessary in areas of shallow claystone bedrock to see that footing foundations are not supported on or immediately above those moderately to highly expansive materials. In this area, overexcavation and backfill techniques with the use of footing foundations or the use of drilled caisson foundations could be considered for foundation support. Geotechnical recommendations concerning design and construction of foundations and support of floor slabs and pavements are presented in the attached report. CENTRE FOR ADVANCED TECHNOLOGY 2301 RESEARCH BOULEVARD, SUITE 104 FORT COLLINS, COLORADO 80526 970) 224- 1 522 (FAx) 224-4564 Earth Engineering Consultants, Inc. EEC Project No. 1972027 May 5, 1997 Page 2 We appreciate the opportunity to be of service to you on this project. If you have any questions concerning this report, or if we can be of further service to you in any other way, please do not hesitate to contact us. Very truly yours. Earth Engineering Consultants, Inc. Lester L. Litton, P.E. Principal Engineer LLL/dmf In SUBSURFACE EXPLORATION REPORT PROPOSED HARMONY RIDGE P.U.D. FORT COLLINS, COLORADO EEC PROJECT NO. 1972027 INTRODUCTION May 5, 1997 The subsurface exploration for the proposed Harmony Ridge P.U.D. in Fort Collins, Colorado, has been completed. Thirteen (13) soil borings extending to depths of approximately 15 to 20 feet below present site grades were advanced in the proposed development area to develop information on existing subsurface conditions. Individual boring logs and a diagram indicating the approximate boring locations are included with this report. The Harmony Ridge P.U.D. will be constructed south of Harmony Road and east of South Taft Hill Road in Fort Collins, Colorado. Borings B-2 through B-11 were completed in the Phase 1 area of the project and borings B-1, B-12 and B-13 were completed in the Phase 2 area. We understand the Harmony Ridge development will include single-family and multi -family residential structures. We anticipate the site structures will be one and two-story wood frame buildings which will likely include full basements. Foundation loads for the residential structures are expected to be light with continuous wall loads less than 2.5 kips per lineal foot and column loads less than 50 kips. Floor loads are estimated to be less than 100 psf. Small grade changes, with cuts and fills less than 2 to 3 feet, are expected to develop the site grades. The purpose of this report is to describe the subsurface conditions encountered in the borings, analyze and evaluate the test data and provide geotechnical recommendations concerning design and construction of foundations and support of floor slabs and pavements. EXPLORATION AND TESTING PROCEDURES The boring locations were established in the field by others prior to our subsurface exploration. A diagram indicating the approximate boring locations is included with this report. Earth Engineering Consultants, Inc EEC Project No. 1972027 May 5, 1997 Page 2 Earth Engineering Consultants, Inc. (EEC) personnel were on site during drilling to evaluate the subsurface conditions encountered and direct the drilling activities. Field logs prepared by EEC personnel were based on visual and tactual observation of disturbed samples and auger cuttings. The final boring logs included with this report may contain modifications to those field logs based on results of laboratory testing and engineering evaluation. The borings were performed using a truck -mounted, rotary -type drill rig equipped with a hydraulic head employed in drilling and sampling operations. The boreholes were advanced using 4-inch nominal diameter continuous flight augers and samples of the subsurface materials encountered were obtained using split -barrel (ASTM Specification D-1586) and California barrel sampling procedures. In those sampling procedures-, standard sampling barrels are driven into the ground using a 140-pound hammer falling a distance of 30 inches. In the California sampling procedure, samples of the subgrade materials are recovered in brass liners to permit "undisturbed" laboratory testing. The number of blows required to advance the sampler is recorded and is used to estimate the in -situ relative density of cohesionless soils and, to a lesser degree of accuracy, the consistency of cohesive soils and hardness of weathered bedrock. All samples obtained in the field were sealed and returned to the laboratory for further examination, classification and testing. Laboratory testing on the recovered samples included moisture content tests of all samples. In addition, the unconfined strength of appropriate samples was estimated using a calibrated hand penetrometer. Atterberg limits and washed sieve analysis tests were performed on selected samples to evaluate the quantity of fines and plasticity of fine materials in the subgrades. Washed Gradation tests were also performed on representative portions of granular soil samples. Swell/consolidation tests were performed on selected samples of the claystone bedrock. Results of the outlined tests are shown on the attached boring logs and summary sheets. As a part of the testing program, all samples were examined in the laboratory by an engineer and classified in accordance with the attached General Notes and the Unified Soil Classification System, based on the soil's texture and plasticity. The estimated group symbol for the Unified I I I Ll I LI Ll Earth Engineering Consultants, Inc. EEC Project No. 1972027 May 5, 1997 Page 3 Soil Classification System is shown on the boring logs and a brief description of that classification system is included with this report. SITE AND SUBSURFACE CONDITIONS The Harmony Ridge P.U.D. will be located south of Harmony Road and east of South Taft Hill Road in Fort Collins, Colorado. The south boundary of the site is, in essence, the Trilby lateral. Surface drainage across the site is to the south with maximum difference in ground surface elevations on the order of 30 feet. Much of the fall on the site occurs towards the southern boundaries. The development area i§ presently covered with sparse grasses and weeds. Evidence of prior building construction was not observed at the site by EEC field personnel. Based on the results of the field borings and laboratory testing, subsurface conditions can be generalized as follows. Approximately 3 to 4 inches of vegetation and/or topsoil was encountered at the surface at the boring locations. The topsoil/vegetation was underlain by reddish brown sands with varying amounts of silt, clay and gravel. The granular and essentially granular soils contained occasional silty and clayey zones and occasional zones containing cleaner granular materials. The very near surface material generally contained more silt and clay. The granular/essentially granular materials extended to the bottom of borings B-1, B-3, B-4 and B-5 at depths of approximately 14 to 20 feet. In boring B-2, the boring was terminated with auger refusal on a zone of cemented sand. At the other boring locations, the granular and essentially granular soils extended to depths of approximately 5 t/2 to 15 feet. The essentially granular soils were underlain by weathered and highly weathered claystone bedrock. The claystone bedrock was colored brown and olive brown and was moderately to highly plastic. Those materials would be subject to volume change with variation in moisture content. The bedrock extended to the bottom of the borings at depths of approximately 15 to 20 feet below present site grades. Earth Engineering Consultants, Inc. EEC Project No. 1972027 May 5, 1997 Page 4 The stratification boundaries indicated on the boring logs represent the approximate location of changes in soil and rock types, in -situ, the transition of materials may be gradual and indistinct. WATER LEVEL OBSERVATIONS Observations were made while drilling and after completion of the borings to detect the presence and depth of hydrostatic groundwater. At the time of drilling, free water was observed only in borings B-10, B-12 and B-13 at depths of approximately 10 to 20 feet. Approximately 24 hours after drilling, free water was observed at depths of 6 feet to 19 feet in borings B-7, B-10, B-11, B-12 and B-13. With the granular, overburden soils, we anticipate the depth to groundwater observed reflects the approximate depth to the groundwater table or perched groundwater at the time of drilling. Zones of perched and/or trapped water may be encountered in more permeable zones interbedded with silty and clayey soils. In addition, perched water is commonly encountered in soils immediately overlying less permeable highly weathered bedrock. The location and amount of perched water and the depth to the hydrostatic groundwater table can vary over time depending on variations in hydrologic conditions and other conditions not apparent at the time of this report. ANALYSIS AND RECOMMENDATIONS Foundations Based on materials observed at the test boring locations, we expect that most of the site structures could be supported on conventional footing foundations bearing in the natural granular and essentially granular soils. In boring B-8, claystone bedrock was encountered at a depth of approximately 51/2 feet. The claystone bedrock should not be used for direct support of the footing foundations. In areas where claystone is encountered within 3 feet of foundation bearing level, overexcavation and backfill procedures could be used to develop foundation bearing for footing foundations. As an alternative, use of a drilled pier foundation system in these areas could also Earth Engineering Consultants, Inc. EEC Project No. 1972027 May 5, 1997 Page 5 be considered. Recommendations are provided below for support of footing foundations on the natural soils or on newly placed and compacted fill. Alternative recommendations for use of drilled pier support are also provided. Footing Foundations - Natural Soils We recommend footing foundations for the proposed lightly loaded residential structures extend through all existing vegetation and/or topsoil and bear in the natural, medium dense reddish brown sand with varying amounts of silt, clay and gravel. For design of footing foundations bearing in the natural, medium dense granular; and essentially granular soils, we recommend using a net allowable total load soil bearing pressure not to exceed 2,500 psf. The net bearing pressure refers to the pressure at foundation bearing level in excess. of the minimum surrounding overburden pressure. Total load should include full dead and live loads. Exterior foundations and foundations in unheated areas should be located a minimum of 30 inches below adjacent exterior grade to provide frost protection. Footing foundations should also be supported at least 3 feet above the highly weathered claystone bedrock. If footing foundations would extend to bear within 3 feet of the claystone bedrock we recommend overexcavation and backfill procedures or use of drilled caisson foundations (as subsequently recommended in this report) be used. We recommend formed continuous footings have a minimum width of 16 inches and isolated column foundations have a minimum width of 24 inches. Trenched foundations or grade beam foundations should not be used for support in the granular soils. Close observation and testing should be completed during construction to see that footing foundations are supported at least 3 feet above the claystone bedrock. Care should also be taken during construction to avoid disturbing the foundation bearing materials. Foundation bearing soils which are loosened or disturbed by the construction activities or materials which become dry and desiccated or wet and softened should be removed and replaced or reworked in place prior to construction of the footings. a 0 0 Earth Engineering Consultants, Inc. EEC Project No. 1972027 May 5, 1997 Page 6 We estimate the long-term settlement of footing foundations designed and constructed as outlined above would less than I inch. 0 Footing Foundations - Overexcavation/Backfill In areas where claystone bedrock is encountered within 3 feet of proposed foundation bearing level, overexcavation and backfill procedures could be considered to develop a zone of at least 3 feet of non -volume change fill between the bedrock and the footing foundations. For this approach, all highly weathered claystone bedrock should be removed from beneath the footing foundations to a depth of at least 3 feet beneath foundation bearing and to a lateral extent of at least 5 feet beyond the building perimeter. Backfill materials for placement in the overexcavation area should consist of approved, low - volume change materials which are free from organic matter and debris. The near surface granular and essentially granular soils could be used as backfill in this area. The claystone bedrock should not be used as fill or backfill beneath the structure. The backfill materials should be placed in loose lifts not to exceed 9 inches thick, adjusted in moisture content and compacted to at least 98 % of the materials maximum dry density as determined in accordance with ASTM Specification D-698, the standard Proctor procedure. The moisture content of the backfill soils should be adjusted to be within the range of ±2 % of standard Proctor optimum moisture. For design of footing foundations bearing on the properly placed and compacted backfill soils, we recommend using a net allowable total load soil bearing pressure not to exceed 2.500 psf. Minimum footing depths and sizes as outlined for footing foundations bearing on the natural soils would apply to footing foundations bearing on the overexcavation and backfill materials. If the backfill materials are disturbed by construction activities prior to placement of foundation concrete, those materials should be reworked in place or removed and replaced prior to placement of footing foundation concrete. 0 0 EEC Project No. 1972027 Earth Engineering Consultants, Inc. May 5, 1997 Page 7 We estimate the long-term settlement of footing foundations supported on properly placed and compacted backfill soils as outlined above would be less than 1 inch. Some risk of movement with moisture fluctuations in the underlying highly weathered claystone bedrock would remain for the footings supported on the backfill soils. Use of a greater thickness of non -volume change material between the bedrock and the footing foundation would reduce that risk. Drilled Caisson Foundations As an alternative to overexcavation in backfilling, drilled piers could also be considered in areas where claystone bedrock is observed within 3 feet of foundation bearing level for conventional footings. The drilled caissons would derive,support through friction and end bearing pressure in the highly weathered claystone bedrock and would resist uplift pressures through friction between the drilled shaft and the surrounding bedrock in the lower portions of the piers. We recommend the drilled pier foundations extend at least 12 feet below the bottom of grade beam elevation or penetrate the bedrock at least 10 feet, whichever provides the greater length of drilled pier. For design of the drilled caisson foundations, we recommend using a total load end bearing pressure not to exceed 20 kips per square foot. A skin friction value of 2,000 psf could be used for that M portion of the drilled shaft penetrating the highly weathered bedrock. We recommend the drilled caisson foundations have a minimum dead load pressure of 5,000 psf. If this dead load cannot be achieved, the drilled caisson could be lengthened and friction between the bedrock and caisson shaft used to make up the difference between required dead load pressure and pressure obtained through dead load. A friction value of 2,000 psf could be used for that portion of the pier extending below the above -outlined minimums. The drilled caissons should be reinforced full length to accommodate transfer of frictional forces between the upper and lower portions of the drilled shafts. Grade beams spanning between the caissons should have a void of at least 4 inches constructed between the bottom of the grade beams and underlying bedrock. That void should be formed with cardboard void boxes or other acceptable methods to prevent filling of the voids with sloughing from the trenches. Ll EEC Project No. 1972027 Earth Engineering Consultants, Inc. May 5, 1997 Page 8 Based on materials we observed at the test boring locations, we do not believe that steel casing will be required during construction to prevent an influx of soil water into the drilled shafts. The drilled pier concrete should be placed as soon as practical after completing the excavation to avoid wetting or drying of the bearing materials. Care should taken during construction to avoid mushrooming of the tops of the drilled caisson shafts. We estimate the long-term settlement of drilled caissons designed and constructed as outlined above would be less than '/2 inch. If a portion of the residence is supported on footing foundations and the remainder of the residence supported on drilled caissons, some differential movement should be anticipated between those pprtions of the residence. The use of drilled piers would not eliminate the risk of movement due to moisture fluctuations in the expansive bedrock; however, Iwe believe that risk would be small. Below Grade Areas We recommend a perimeter drain system be installed around all below grade areas to reduce the potential for a buildup of hydrostatic loads on below grade walls and/or infiltration of surface water into below grade areas. In general, a perimeter drain system would consist of perforated metal or plastic pipe placed at approximate foundation bearing level around the exterior perimeter of the structure. If drilled caissons are used, the perimeter drain would be placed near the base of the exterior grade beam. The drain line should be sloped to provide positive drainage to a sump area where water can be removed without reverse flow into the system or to a gravity outfall where reverse flow was prevented. The drain line should be surrounded by a minimum of 6 inches of appropriately sized granular filter soil and either the filter soil or the drain line should Ibe surrounded by an appropriate filter fabric to prevent an influx of fines into the system. Backfill placed above the perimeter drain line should consist of approved, low -volume change materials which are free from organic matter and debris. The near surface granular and essentially granular soils could be used as backfill in these areas; the highly weathered claystone should not be used as backfill. We recommend the top 2 feet of material contain sufficient fines to reduce EEC Project No. 1972027 Earth Engineering Consultants, Inc. May 5, 1997 Page 9 the potential for surface infiltration around the structure. The backfill material should be placed in loose lifts not to exceed 9 inches thick, adjusted in moisture content and compacted to at least 90% of the material's maximum dry density as determined in accordance with the standard Proctor procedure. Backfill materials which will support patios, sidewalks, steps, pavements or similar improvements should be compacted to at least 95 % of standard Proctor maximum dry density. The moisture content of the fill soils should be adjusted to be within the range of t2% of standard Proctor optimum moisture at the time of compaction. For design of below grade walls for residential structures, active lateral earth pressure analysis is commonly used. The active analysis assumes slight rotation will occur; that rotation is generally assumed to be 0.5 % of the wall height. Tnt design of below grade walls using the active lateral stress distribution assumptions, we recommend using.,an equivalent fluid pressure of 35 pounds per cubic foot. That lateral pressure does not contain a factor of safety nor an allowance for hydrostatic loads. Floor Slab and Pavement Subgrades The near surface granular and essentially granular soils could be used for direct support of pavements. In areas where the structures will be supported on footing foundations. including both the overexcavation and backfill support and the natural soil support, the floor slabs could be supported as slab -on -ground. If drilled caisson foundations will be used to support the proposed residence, we recommend a structural floor be used. Recommendations for both of floor types are provided below. IFloor Slab on Ground/Pavement Subgrades Where floor slabs or pavements will be supported on existing granular/essentially granular or on newly placed and compacted fill soils, all existing vegetation and/or topsoil should be removed from the floor slab and pavement areas. After stripping and completing all cuts and prior to placement of any till, floor slabs or pavements, we recommend the exposed subgrades be scarified Earth Engineering Consultants, Inc. EEC Project No. 1972027 May 5, 1997 Page 10 to a minimum depth of 9 inches, adjusted in moisture content and compacted to at least 95 % of the material's standard Proctor maximum dry density. The moisture content of the scarified soils should be adjusted to be within ±2 % of standard Proctor optimum moisture at the time of compaction. Scarification and recompaction would not be required in the basement areas of the structures. In areas where slopes are steeper than 4 horizontal to 1 vertical, benching of the subgrade should be completed prior to fill placement. Benching will reduce potential for development of a slip plane between the in -place soils and newly placed fill. Fill soils required to develop the floor slab -or pavement subgrade should consist of approved, low volume change materials from organic matter and debris. Soils similar to the near surface silty sand soils could be used as fill in these areas. The claystone bedrock should not be used as fill beneath any of the on -site improvements. We recommend the fill soils be placed in loose lifts not to exceed 9 inches thick, adjusted in moisture content as recommended for the scarified soils and compacted to at least 95 % of the material's standard Proctor maximum dry density. Care should be taken after preparation of the floor slab subgrades to avoid disturbing the in -place soils. Materials which are loosened or disturbed by the construction activities or materials which become dry and desiccated or wet and softened should be removed and replaced or reworked in place prior to placement of the overlying floor slabs. Structural Floors In those residences supported on caisson foundations, we recommend structural floors be used in the basement areas of the structures to prevent the underlying subgrades from causing significant movement of the floor slabs and potential damage to upper floors of the building. The crawl space should have a minimum 18 inch space beneath the bottom of the floor joist and the underlying subgrade. Structural floors are often constructed as a wood floor joist and decking system similar Earth Engineering Consultants, Inc EEC Project No. 1972027 May 5, 1997 Page 11 to a conventional first floor level. In this area of the structure, care should be taken to develop a method for removing free water from the subgrade areas. Pavements In accordance with current City of Fort Collins guidelines, pavement section design is completed after approximate final grade has been developed in the pavement areas and utilities have been completed in the roadway areas. The pavement design at that time will be based, in part, on the load carrying characteristics of the materials used to develop the street subgrades. If the on -site granular and essentially granular soils are used to develop the subgrades, we expect the current City of Fort Collins minimum sections will meet the design criteria. The current recommended minimum section for a "local' street is 31/2 inches of asphalt overlying 6 inches of aggregate base. The pavement section recommendation may vary from that minimum based on traffic projections provided by the City of Fort Collins) and determined load carrying characteristics of the site soils. GENERAL COMMENTS The analysis and recommendations presented in this report are based upon the data obtained from the soil borings performed at the indicated locations and from any other information discussed in this report. This report does not reflect any variations which may occur between borings or across the site. The nature and extent of such variations may not become evident until construction. If variations appear evident, it will be necessary to re-evaluate the recommendations of this report. It is recommended that the geotechnical engineer be retained to review the plans and specifications so that comments can be made regarding the interpretation and implementation of our geotechnical recommendations in the design and specifications. It is further recommended that the geotechnical engineer be retained for testing and observations during earthwork and foundation construction phases to help determine that the design requirements are fulfilled. Earth Engineering Consultants, Inc. EEC Project No. 1972027 May 5, 1997 Page 12 This report has been prepared for the exclusive use of Positive Environments, Inc. for specific application to the project discussed and has been prepared in accordance with generally accepted geotechnical engineering practices. No warranty, express or implied, is made. In the event that any 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 the changes are reviewed and the conclusions of this report modified or verified in writing by the geotechnical engineer. I DRILLING AND EXPLORATION 0 C I I I I I I I I 11 DRILLING & SAMPLING SYMBOLS: SS: Split Spoon - 13/8" I.D., 2" O.D., unless otherwise noted PS: Piston Sample ST: Thin -Walled Tube - 2" O.D., unless otherwise noted WS: Wash Sample R: Ring Barrel Sampler - 2.42" I.D., 3" O.D. unless otherwise noted PA: Power Auger FT: Fish Tail Bit HA: Hand Auger RB: Rock Bit DB: Diamond Bit = 4", N, B BS: Bulk Sample AS: Auger Sample PM: Pressure Meter HS: Hollow Stem Auger WB: Wash Bore Standard "N" Penetration: Blows per foot of a 140 pound hammer falling 30 inches on a 2-inch O.D. split spoon, except where noted. WATER LEVEL MEASUREMENT SYMBOLS: WL : Water Level WS : While Sampling WCL Wet Cave in WD : While Drilling DCI: Dry Cave in BCR: Before Casing Removal AB : After Boring ACR: After Casting Removal Water levels indicated on the boring logs are the levels measured in the borings at the time indicated. In pervious soils, the indicated levels may reflect the location of ground water. In low permeability soils, the accurate determination of ground water levels is not possible with only short term observations. DESCRIPTIVE SOIL CLASSIFICATIOX Soil Classification is based on the Unified Soil ClassificatioYr- system and the ASTM Designations D-2488. Coarse Grained Soils have move than 50% of their dry weight retained on a #200 sieve; they are described as: boulders, cobbles, gravel or sand. Fine Grained Soils have less than 50% of their dry weight retained on a #200 sieve; they are described as : clays, if they are plastic, and silts if they are slightly plastic or non -plastic. Major constituents may be added as modifiers and minor constituents may be added according to the relative proportions based on grain size. In addition to gradation, coarse grained soils are defined on the basis of their relative in -place density and fine grained soils on the basis of their consistency. Example: Lean clay with sand, trace gravel, stiff (CL); silty sand, trace gravel, medium dense (SM). CONSISTENCY OF FINE-GRAINED SOILS Unconfined Compressive Strength, Qu, psf Consistency 500 Very Soft 500 - 1,000 Soft 1,001 - 2,000 Medium 2,001 - 4,000 Stiff 4,001 - 8,000 Very Stiff 8,001 - 16,000 Very Hard RELATIVE DENSITY OF COARSE -GRAINED SOILS: N-Blows/ft Relative Density 0-3 Very Loose 4-9 Loose 10-29 Medium Dense 30-49 Dense 50-80 Very Dense 80 + Extremely Dense PHYSICAL PROPERTIES OF BEDROCK DEGREE OF WEATHERING: Slight Slight decomposition of parent material on joints. Maybe color change. Moderate Some decomposition and color change throughout. High Rock highly decomposed, may be extremely broken. HARDNESS AND DEGREE OF CEMENTATION: Limestone and Dolomite: Hard Difficult to scratch with knife. Moderately Can be scratched easily with knife. Hard Cannot be scratched with fingernail. Soft Can be scratched with fingernail. Shale Siltstone and Cla stone: ar an a scratched easily with knife, cannot be scratched with fingernail. Moderately Can be scratched with fingernail. Hard Soft Can be easily dented but not molded with fingers. Sandstone and Conglomerate: Weff Capable of scratching a knife blade. Cemented Cemented Can be scratched with knife. Poorly Can be broken apart easily with fingers. Cemented I UNIFIED SOIL CLASSIFICATION SYSTEM 10 Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests' Coarse -Grained Gravels more than Cleans Gravels Less Soils more than 50% of coarse than 5% finesc 50% retained on fraction retained No. 200 sieve on No. 4 sieve Gravels with Fines more than 12% fines' Sands 50% or Clean Sands Less more of coarse than 5% fines'` fraction passes No. 4 sieve Sands with Fines more than 12% fi lies° Fine -Grained Silts and Clays inorganic Soils 50% or Liquid limit less more passes the than 50 No. 200 sieve organic Silts and Clays inorganic Liquid limit 50 or more organic Cu>4and I <Cc<3' Cu < 4 and/or I > Cc > 3" Fines classify as ML or MH Fines classify as CL or CH Cu > 6 and l < Cc < 3" Cu < 6 and/or 1 > Cc > 3" Fines classify as ML or MH Fines classify as CL or CH PI > 7 and plots on or above "A" line PI < 4 or plots below "A" I me Liquid limit - oven dried Liquid limit - not dried PTI) ots on or above "A" line PI lots below "A'"line Liquid limit -oven dried Liquid limit - not dried Highly organic soils Primarily organic matter, dark in color, and organic odor Based on the material passing the 3-in. (75- ECu=D60/Dice= (D30) mm) sieve D X D If field sample contained cobbles or boulders, or both, add "with cobbles or boulders, or both" to group name. If soil contains> 15%sand, add "with sand" to Gravels with 5 to 12% fines require dual group name. symbols: If fines classify as CL-ML, use dual symbol GW-GM well -graded gravel with silt GC -CM, or SC-SM. GW-GC well -graded gravel with clay If fines are organic, add "with organic fines" to GP -GM poorly graded gravel with silt roup name. GP -GC poorly graded gravel with clay Ifsoil contains> 15%gravel, add "with gravel" Sands with 5 to 12% fines require dual to group name_ symbols: If Atterberg limits plot in shaded area, soil is a SW-SM well -graded sand with silt CL-ML, silty clay. SW -SC well -graded sand with clay SP-SM poorly graded sand with silt SP-SC poorly graded sand with clay c 0.7 0.7 Soil Classification Group Group Name" Symbol GW Well -graded gravef GP Poorly graded gravel GM Silty gravel, G. H GC Clayey gravel' " " SW Well -graded sand' SP Poorly graded sand' SM Silty sand"•" ' SC Clayey sand""'' CL Lean clay"-" 4 ML Silt"' M Organic clay"­" 5 OL Organic silt"' ""' CH Fat clay" A4 MH Elastic Silt" -"' o rganic clay"`•"'•'' 5 OH Organic silt"­m` PT Peat If soil contains 15 to 29% plus No. 200, add with sand" or "with gravel", whichever is predominant. if soil contains _> 30% plus No. 200 predominantly sand, add "sandy" to group name. lf soil contains _> 30% plus No. 200, predominantly gravel, add "gravelly" to group name. PI > 4 and plots on or above "A" line. I'M < 4 or plots below "A" line. PI plots on or above "A" line. API plots below "A" line. z 00 4m 3(im3NI lON r`0 I I0 cm m LO 0 m 0m O m i To 0 / m / rl w O m O 0m / N N QQ Q m = , a_ F- m 0 I 0mm .% 3NIl_35VHd__ r 3NIl 1OVM1 IJ V) Q GMJ 71H iJVi HinoS r- rn O a O 0 IJ Q U5 W O JQ O 0 Cr) LLJ a Z Q C) J ZO O U Q U O O 1 J D W N Z C) O CN mom°' Z O Q Z U III O Ir n cn E- z a