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Home My WebLink About20051314.tiff J f PRELIMINARY GEOTECHNICAL ENGINEERING REPORT N.C. RANCH - MINOR SUBDIVISION SOUTH SIDE OF HWY 66 BETWEEN COUNTY LINE ROAD AND WCR 3 WELD COUNTY, COLORADO TERRACON PROJECT NO. 22015241 November 27, 2001 Prepared for Kimberly Stenerson 6364 Clearwater Road Boulder, Colorado 80303 Prepared by: Terracon 1242 Bramwood Place, Suite 2 Longmont, Colorado 80501 Phone: 303-776-3921 Fax: 303-776-4041 2005-1314 llerracon— lierracon November 27, 2001 1242 Bramwood PI Longmont.Colorado 80501 (303)776-3921 Fax. 1303)776-4041 Kimberly Steverson 6364 Clearwater Road Boulder, Colorado 80303 Re: Preliminary Geotechnical Engineering Report N.C. Ranch — Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County, Colorado Terracon Project No. 22015241 Terracon has completed our preliminary geotechnical engineering exploration for the proposed N.C. Ranch minor subdivision to be located on the south side of Colorado State Highway 66 between County Line Road and Weld County Road 3 northeast of Longmont, Colorado. The accompanying geotechnical report presents our findings and preliminary recommendations concerning potential site development constraints, general earthwork, foundation systems, floor slabs, septic systems and pavement construction for the proposed development. The preliminary recommendations presented in this report are intended for planning purposes. A design level geotechnical investigation will be required on each lot in order to design and construct foundations, floor slabs and septic systems. The subsurface conditions encountered in our borings generally consisted of about 3% to 12 feet of very stiff to hard lean to fat clays with varying amounts of sand overlying sedimentary claystone bedrock. Groundwater was recorded in Boring 1 at a depth of about 11% feet below the ground surface 1 day after drilling. The other borings remained dry to the depths explored. It should be recognized that groundwater levels will likely fluctuate over time in response to irrigation demands on or adjacent to the site, fluctuations in water levels of adjacent water features, weather and seasonal conditions. The results of our field exploration and laboratory testing completed for this study, indicate that the site clays and the claystone bedrock typically show high to very high swell potential when wetted. Although the swell potential of the claystone appeared to decrease somewhat with depth. The bedrock is considered to have high load bearing capability. Based on the preliminary data from this investigation, it appears that lightly loaded residential structures constructed on the site will need to be supported on grade beam and drilled pier (caisson) foundation systems in order to mitigate the risk of foundation movement. Arizona■Arkansas IN Colorado■Georgia■Idaho■Illinois■Iowa■Kansas•Kentucky■Minnesota■Missoun Montana■Nebraska■Nevada■New Mexico■Oklahoma I•Tennessee■Texas■Utah■Wisconsin■Wyoming Ouplity Engineering Since 1965 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch—Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 Current groundwater conditions indicate that basement construction should be practical on the majority of the site unless deeper than normal basement cuts are planned. However, due to the potential for groundwater fluctuations and/or the development of perched/trapped groundwater on top of the bedrock, foundation drainage systems should be anticipated for all below grade levels. In general, we recommend placing basement floors at least 3 feet above the level of groundwater. The clays and claystone bedrock found on this site are judged to present a high to very high risk of slab heave and associated cracking. Based on the preliminary swell data we estimate potential slab heave of 3 to 6 inches for this site. Accordingly, structural floors with a void space beneath it should be expected for all residences with basements constructed at the site. Other preliminary design and construction recommendations, based upon geotechnical conditions encountered in our test borings, are presented in the report. We appreciate being of service to you in the preliminary geotechnical engineering phase of this project, and are prepared to assist you during the design level geotechnical and construction phases as well. If you have any questions concerning this report or any of our testing, inspection, design and consulting services, please do not hesitate to contact us. Sincerely, TE =O�p00.fQjsr ttl ;QPpO ••••. Ott %t C s. 10% ease l� :: - PFD J.A 11 ;�4t„ r N: - ; o�OM/ N • i na c 157 l/ll��_ /� 'y � • 11 •• wa'6:0Eric S. Willis, P.E. Edward J. Paas, P.E. Geotechnical Engineer/Department Manager Principal Copies to: Addressee (3) 2 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch—Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 TABLE OF CONTENTS Page No. Letter of Transmittal INTRODUCTION 1 PROPOSED CONSTRUCTION 2 SITE EXPLORATION 2 Field Exploration 2 Laboratory Testing 3 SITE CONDITIONS 3 SUBSURFACE CONDITIONS 4 Geology 4 Soil and Bedrock Conditions 5 Field and Laboratory Test Results 5 Groundwater Conditions 5 ENGINEERING ANALYSIS AND RECOMMENDATIONS 6 Site Development and Geotechnical Considerations 6 Site Grading/Earthwork Recommendations 7 Utility Construction g Foundation Construction 9 Basement Construction 9 Slab on Grade Construction 10 Surface Drainage 10 Septic System Construction 10 Pavement Construction 11 Corrosion Protection (Concrete) 12 GENERAL COMMENTS 12 3 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch-Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 TABLE OF CONTENTS (CONTINUED) APPENDIX A Test Boring Location Plan Al Logs of Borings A2 thru A5 APPENDIX B Swell-Consolidation Test Curves B1 thru B9 Grain Size Distribution Curves/Soil Classification 810 APPENDIX C: General Notes: Drilling & Exploration Cl Unified Soil Classification C2 Rock Classification C3 4 PRELIMINARY GEOTECHNICAL ENGINEERING REPORT N.C. RANCH-MINOR SUBDIVISION SOUTH SIDE OF HWY 66 BETWEEN COUNTY LINE ROAD AND WCR 3 WELD COUNTY, COLORADO TERRACON PROJECT NO. 22015241 November 27, 2001 INTRODUCTION This report contains the results of our preliminary geotechnical engineering exploration for the proposed N.C. Ranch minor subdivision to be located on the south side of Colorado State Highway 66 between County Line Road and Weld County Road 3 northeast of Longmont, Colorado. The site is located in the Northeast 1/4 of Section 30, Township 3 North, Range 68 West of the 6th Principal Meridian in Weld County, Colorado. The purpose of these services is to provide information and preliminary geotechnical engineering recommendations relative to: • subsurface soil and bedrock conditions • groundwater conditions • general earthwork considerations • utility construction/excavations • foundation construction • basement construction • floor slab construction • septic systems • pavement construction The conclusions and preliminary recommendations contained in this report are based upon the results of field and laboratory testing, engineering analyses, and experience with similar soil conditions, structures and our understanding of the proposed project. The preliminary recommendations presented in this report are intended for planning purposes only. Additional investigations will be required in order to design foundations, floor slabs, septic systems and pavements. 1 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch—Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 PROPOSED CONSTRUCTION Based on information provided by the client, the project will involve subdividing the 40-acre tract of land into 3 to 9 residential building sites. Preliminary information indicates that the lots could range in size from approximately 1 to 20 acres. A private road will also be constructed to provide access to the lots and underground utilities (water lines only) will be installed below the street. We anticipate that the proposed residences will be single to two- story wood frame structures with basements. Considering the size and type of construction planned, we anticipate relatively light residential foundation loads. Other site development features will include the construction of individual sewage disposal systems (ISDS) to serve the proposed residences. Site grading plans were not available at the time of this report. Therefore, the magnitude of site grading cuts or fills (if any) are not known. We should be contacted to review site grading plans when they become available. SITE EXPLORATION • The scope of the services performed for this project included site reconnaissance by a geotechnical engineer, a subsurface exploration program, laboratory testing and engineering analysis. Field Exploration: A total of 4 deep test borings were drilled on November 13, 2001. The borings were drilled to depths of about 15 to 25 feet at the approximate locations shown on the Boring Location Plan, Figure 1. In addition, a shallow test hole was drilled next to each of the deep borings, for preliminary percolation testing. Borings were advanced with a truck- mounted drilling rig, utilizing 4 or 6-inch diameter solid stem auger. The borings were located in the field by pacing or measurements with a surveying wheel using property boundaries and/or existing site features as a reference. Right angles for locating the borings were estimated. Elevations of borings were not surveyed and logs are drawn to depth. The accuracy of boring locations should only be assumed to the level implied by the method used. Lithologic logs of each boring were recorded by the geotechnical engineer during the drilling operations. At selected intervals, samples of the subsurface materials were taken by driving California barrel samplers. Penetration resistance measurements were obtained by driving the California barrel into the subsurface materials with a 140-pound hammer falling 30 inches. The penetration resistance value is a useful index in estimating the consistency, relative density or hardness of the materials encountered. In addition, groundwater conditions were recorded in each boring at the time of site exploration, and approximately 24 hours after completion of drilling. 2 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch-Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 Laboratory Testing: Samples retrieved during the field exploration were returned to the laboratory for observation by the project geotechnical engineer, and were visually or manually classified in general accordance with the Unified Soil Classification System described in Appendix C. Samples of bedrock were classified in general accordance with the notes for Rock Classification described in Appendix C. At that time, the field descriptions were confirmed or modified as necessary and an applicable laboratory testing program was formulated to determine engineering properties of the subsurface materials. Boring logs were prepared and are presented in Appendix A. Laboratory tests were conducted on selected soil samples and are presented in Appendix B. The test results were used for the geotechnical engineering analyses, and the development of preliminary foundation and earthwork recommendations. Laboratory tests were performed in general accordance with the applicable local or other accepted standards. Selected soil samples were tested for the following engineering properties: • Water Content Grain size • Dry Density • Plasticity Index • Swell-consolidation • Water Soluble Sulfate Content • Compressive Strength SITE CONDITIONS The project site is located on the south side of Colorado State Highway 66 between County Line Road and Weld County Road 3 northeast of Longmont, Colorado. The property appears to have been used for agricultural purposes and/or crop production in the past. In general, the property is surrounded by open agricultural land; although, a rural residential development is located to the west of the site. The ground surface at the site is relatively uniform with a general slope downward to the west and south. However, a relative low-point appears to exist to the west of our Test Boring 2 and is coincident with a gentle swale and a depression. Review of USGS 7.5 minute series topographic maps indicates a maximum difference in elevation of about 35 feet across the property. Surface slopes are estimated to be on the order of VA to 5 percent. The ground surface at the site is typically vegetated with native weeds, grasses and some scattered brush. Other features on or adjacent to the site included a small irrigation lateral which crosses the site from the east to west between our test borings 3 and 4 and Union Reservoir which is located downhill and approximately 1,500 feet to the south of the site. 3 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch—Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 SUBSURFACE CONDITIONS Geology: The project area is located within the Colorado Piedmont section of the Great Plains physiographic province. The Colorado Piedmont, formed during Late Tertiary and Early Quaternary time (approximately 2,000,000 years ago), is a broad, erosional trench which separates the Southern Rocky Mountains from the High Plains. Structurally, the site lies along the western flank of the Denver Basin. During the Late Mesozoic and Early Cenozoic Periods (approximately 70,000,000 years ago), intense tectonic activity occurred, causing the uplifting of the Front Range and associated downwarping of the Denver Basin to the east. Relatively flat uplands and broad valleys characterize the present-day topography of the Colorado Piedmont in this region. Surficial geologic conditions mapped in the general vicinity of the site (1Tweto, 1979), consist of Eolian deposits (Qe). Bedrock mapped in the vicinity of the site consists of the Upper Unit of the Pierre Shale (Kpu) and was encountered in our borings at depths ranging from about 3% to 12 feet below the ground surface. Our field investigation generally confirmed the conditions anticipated from the geologic map. No economically extractable minerals are known to occur below the subject site. Mapping completed by the Colorado Geological Survey (2Amuedo and Ivey, 1975), indicates that there is no record of underground coal mining activities below the subject site and that the site does not lie within a subsidence hazard zone as defined by the Amuedo and Ivey study. Due to the relatively flat nature of the property, geologic hazards at the site are anticipated to be low. Seismic activity in the area is anticipated to be low; and from a structural standpoint, the property should be relatively stable. With proper site grading around proposed structures, erosional problems at the site should be minor. Mapping completed by the Colorado Geological Survey (3Hart, 1972), indicates the site in an area of "Moderate to High Swell Potential". Potentially expansive materials mapped in this area include bedrock, weathered bedrock and colluvium (surficial units). Site specific swell 'Tweto,Ogden, 1979 Geologic Map of Colorado,United States Geological Survey. 2Amuedo 8 Ivey, 1975, Ground Subsidence and Land-Use Considerations Over Coal Mines in the Boulder-Weld Coal Field, Colorado,Colorado Geological Survey,Environmental Geology No.9. Hart, Stephen S., 1972, Potentially Swelling Soil and Rock in the Front Range Urban Corridor, Colorado, Colorado �..� Geological Survey, Environmental Geology No.7. 4 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch—Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 testing conducted for this study indicates that the site clays and the claystone bedrock typically exhibit high to very high swell potential. Soil and Bedrock Conditions: As presented on the Logs of Boring, a thin mantle of soil with light vegetation and root growth was encountered at the surface in all of our borings. The subsurface soils/bedrock encountered in our borings consisted of about 3% to 12 feet of lean to fat clays with varying amounts of sand overlying sedimentary claystone bedrock. Please refer to the Logs of Boring for more comprehensive strata descriptions. Field and Laboratory Test Results: Penetration test results indicate that clay soils vary from very stiff to hard in consistency. Swell-consolidation tests indicate that the clays soils have high to very high swell potential. The bedrock penetrated in our borings varies from slightly weathered to very hard, with hardness increasing somewhat with depth. The claystone bedrock typically shows high to very high swell potential when wetted. Although the swell potential of the claystone appears to decrease somewhat with depth. The bedrock is considered to have high load bearing capability. Subsurface conditions and preliminary percolation tests conducted adjacent to the test borings are summarized below: subsurface Got449.ns and Parcoladon Test Results { .. . ..., .. . ., . . �s<-, . , ..riw�,= s,g; Test Depth soi6 t" Percofatton Rate;,` Deptt to Dspthtam• Hole 1Z4ininutesthijobil Gfoundwater(ft) Bedrocklft)` P-1 35 CL 480 11'1 12 P-2 36 CUCH 240 >15 6 PJ 33 CL 32 >15 3% P-4 28 CL 60 >25 6 Field percolation test results indicate the site soils tested have variable percolation characteristics, ranging from good to poor. Groundwater Conditions: Groundwater was not encountered in any of the test borings to the depths explored at the time of our field investigation. However, when checked approximately 24 hours after drilling, groundwater was measured in Test Boring 1 at a depth of about 11% feet below the ground surface. It should be recognized that groundwater levels will likely fluctuate over time in response to irrigation demands on or adjacent to the site, fluctuations in water levels of adjacent water features, weather and seasonal conditions. 5 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch-Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 In addition, zones of perched and/or trapped groundwater, where not already present, may also occur at times in the subsurface soils overlying bedrock, on top of the bedrock surface or within permeable fractures in the bedrock materials. The location and amount of perched water is dependent upon several factors, including hydrologic conditions, type of site development, irrigation demands on or adjacent to the site, fluctuations in water features, seasonal and weather conditions. Fluctuations in groundwater levels can best be determined by implementation of a groundwater monitoring plan. Such a plan would include installation of groundwater monitoring wells, and periodic measurement of groundwater levels over a sufficient period of time. The possibility of groundwater fluctuations and the development of perched groundwater should be considered when developing design and construction plans for the project. Based upon review of U.S. Geological Survey Maps (4Hillier, et al, 1983), regional groundwater beneath the project area predominates in colluvial, windblown materials, or in fractured weathered consolidated sedimentary bedrock located at a depth near ground surface. Seasonal variations in groundwater conditions are expected since the aquifer materials may not be perennially saturated. Groundwater is generally encountered at depths ranging from 5 to 20 feet below ground surface; depth to seasonal groundwater can be on the order of 10 feet or less. ENGINEERING ANALYSIS AND PRELIMINARY RECOMMENDATIONS Site Development and Geotechnical Considerations: We believe that the primary geotechnical conditions which will impact residential construction on the site are the high to very high swelling clays and claystone bedrock encountered on the site. The risks associated with swelling soils and bedrock can be mitigated by careful design, construction and maintenance practices; however, it should be recognized that these procedures will not necessarily eliminate the risk. Builders and homeowners should be aware and understand that slabs-on-grade and, in some instances, foundations may be affected by the swelling soils and bedrock present on this site. These concerns and other site development considerations are briefly discussed in the following sections. Based on the preliminary data from this investigation, it appears that lightly loaded residential structures constructed on the site will need to be supported on grade beam and drilled pier (caisson) foundation systems in order to mitigate the risk of foundation movement. Hillier, Donald E.; Schneider, Paul A., Jr.; and Hutchinson, E. Carter, 1983, Depth to Water Table(1979) in the Boulder-Fort Collins-Greeley Area,Front Range Urban Corridor,Colorado,United States Geological Survey,Map I-855-I. 6 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch—Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 Current groundwater conditions indicate that basement construction should be practical on the majority of the site unless deeper than normal basement cuts are planned. However, due to the potential for groundwater fluctuations and/or the development of perched/trapped groundwater on top of the bedrock, foundation drainage systems should be anticipated for all below grade levels. In general, we recommend placing basement floors at least 3 feet above the level of groundwater. The clays and claystone bedrock found on this site are judged to present a high to very high risk of slab heave and associated cracking. Based on the preliminary swell data we estimate potential slab heave of 3 to 6 inches for this site. Accordingly, structural floors with a void space beneath it should be expected for all residences with basements constructed at the site. General Site Grading/Earthwork Considerations: Site grading plans were not available for our review at the time of this investigation. We should be contacted to review site grading plans when they become available. Plasticity characteristics of the site clays indicate that these materials can be susceptible to disturbance and loss of strength under repeated wheel loads, particularly at higher moisture contents. This condition can lead to "pumping" soils and unstable subgrades could develop. If unstable conditions develop during earthwork activities, some method of soil improvement or stabilization will be needed prior to pavement or foundation construction. The ground surface in the area of proposed fill placement should be stripped of vegetation and organic matter. This material should be wasted from the site or stockpiled and used to revegetate landscape areas or exposed slopes after completion of grading operations. If it is necessary to dispose of organic materials on-site, they should be placed in non-structural areas and in fill sections not exceeding 5 feet in height. For permanent slopes in compacted fill or cut areas we recommend slopes of 3:1 (horizontal to vertical), or less to reduce erosion and maintenance problems. If steeper slopes or slopes over about 5 to 7 feet in height are required for site development, stability analyses should be completed to design the grading plan. The subgrade beneath proposed fill and pavement areas should be scarified, moisture conditioned within 2 percent of optimum moisture content (unless modified by the geotechnical engineer) and compacted to at least 95 percent of the standard Proctor maximum dry density (ASTM D698). The on site soils or approved low swelling import materials can be used for site grading fill. The fill should be placed in thin, loose lifts and compacted. Spreading and drying of wet soils or moisture addition and uniform mixing of dry soils will be necessary to bring the soils into 7 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch—Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 working moisture ranges and will be important. We recommend fill placed at the site which consists of the on-site soils/bedrock be moisture conditioned at optimum to about 2 to 3 percent above optimum moisture content (unless modified by the geotechnical engineer) and compacted to at least 95 percent of the standard Proctor maximum dry density (ASTM D698). If fill depths exceed about 5 to 7 feet, modifications to the fill placement and compaction criteria may be needed. Fill should not contain frozen material and it should not be placed on a frozen subgrade. Placement and compaction of fill should be observed and tested by the geotechnical engineer to verify that the specified moisture and compaction requirements have been achieved. Utility Construction/Excavation: Excavations into the subsurface materials will likely encounter very stiff to hard clays, claystone bedrock and possibly groundwater and/or perched water depending upon location on the site and depth of excavation. We believe the overburden materials can be excavated with conventional earth-moving or excavation equipment. However, difficult excavation of the bedrock materials should be anticipated. Drilling and blasting to facilitate rock break-up and removal is not anticipated for excavations on the order of 10 to 15 feet or less. The individual contractor(s) should be made responsible for designing and constructing stable, temporary excavations as required to maintain stability of both the excavation sides and bottom. All excavations should be sloped or shored in the interest of safety following local, and federal regulations, including current OSHA excavation and trench safety standards. As a safety measure, it is recommended that all vehicles and soil piles be kept to a minimum lateral distance from the crest of the slope equal to no less than the slope height. Groundwater was recorded in Boring 1 at a depth of about 111/2 feet below the ground surface 1 day after drilling. The other borings remained dry to the depths explored. It should be recognized that groundwater levels will likely fluctuate over time in response to irrigation demands on or adjacent to the site, fluctuations in water levels of adjacent water features, weather and seasonal conditions. Where groundwater or perched water is penetrated in excavations, some method of temporary dewatering will be needed for proper construction. Dewatering should continue through the excavation and backfilling operations to ensure proper construction. Where excavations penetrate the groundwater for only a shallow depth, it may be possible to dewater by sloping the excavation to isolated sumps and pumps. If more permeable soils, such as sands, are encountered or excavations penetrate the groundwater for a significant depth, more extensive dewatering methods, such as well points, may be needed for effective dewatering and groundwater control. The soils to be penetrated by the proposed excavations may vary significantly across the site. The preliminary soil classifications are based solely on the materials encountered in widely spaced exploratory test borings. The contractor should verify that similar conditions 8 • Preliminary Geotechnical Engineering Report Terracon N.C.Ranch—Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 exist throughout the proposed area of excavation. If different subsurface conditions are encountered at the time of construction, we recommend that we be contacted immediately to evaluate the conditions encountered. Foundation Construction: Preliminary data from this investigation indicates that that the clay soils and bedrock likely to influence foundation performance on the site have high to very high swell potential. Therefore, it appears that lightly loaded residential structures constructed on the site will need to be supported on grade beam and drilled pier (caisson) foundation systems in order to mitigate the risk of foundation movement. Minimum pier lengths on the order of 25 feet with minimum bedrock penetrations on the order of 10 to 15 feet should be expected for drilled pier construction on the site. Based on the subsurface conditions, it appears that pier drilling should be possible with conventional drilling equipment and that temporary casing will probably not be needed on most of the site. However, some water seepage should be expected during drilling operations and "drill and pour" construction methods should be employed. In addition, our experience in the area suggests that the bedrock formation can contain water-bearing seams. This condition, if encountered during drilling, will probably require the use of a concrete pump truck with a tremie extension to discharge concrete at the bottom of the pier hole in order to displace the water. A more detailed, site specific geotechnical investigation will be necessary for each building lot in order to develop specific foundation and floor construction recommendations after site grading is complete and final building locations and type of construction have been established. Basement Construction: Groundwater was recorded in Boring 1 at a depth of about 11% feet below the ground surface 1 day after drilling. The other borings remained dry to the depths explored. Current groundwater conditions indicate that basement construction should be practical on the majority of the site unless deeper than normal basement cuts are planned. However, surface water can penetrate relatively permeable and loose backfill adjacent to the residence and collect at the bottom of the excavations resulting in a perched groundwater condition. The provision of a foundation drain should be anticipated for all below grade levels. In general, we recommend placing basement floors at least 3 feet above the level of existing groundwater. Site specific foundation drainage details can be provided following supplemental geotechnical exploration. Basement walls should be designed for the lateral earth pressures imposed by the soil backfill. For preliminary design purposes, we suggest basement walls be designed for an equivalent fluid pressure in the range of 50 to 60 pcf for the on-site soils/bedrock. Fill against foundation walls should be moistened to at or near optimum and well compacted. 9 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch-Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 Compaction of each lift adjacent to walls should be accomplished with hand-operated tampers or other lightweight compactors. Overcompaction may cause excessive lateral earth pressures which could result in wall movement. Slab-on-Grade Construction: Materials encountered at basement floor levels on this site will likely include high to very high swelling clays or claystone bedrock. These materials are judged to present a high to very high risk of slab heave and associated cracking. Based on the preliminary swell data we estimate potential slab heave of 3 to 6 inches for this site. Accordingly, structural floors with a void space beneath it should be expected for basement floors in all residences constructed at the site. Garage floors are normally constructed as slabs-on-grade. Performance of conventional concrete slabs on expansive soils is erratic and slabs will heave and likely crack to some extent when the underlying soils become elevated in moisture content. Heave and differential movement of slab-on-grade construction, for garage areas, could be reduced by removing at least 3 feet of the expansive soils and replacing these materials with non- expansive or low swelling imported fill. Thicker sections of approved fill should further reduce potential slab movement. This alternative will not eliminate the possibility of differential slab movement; however, movements should be reduced and would tend to be more uniform. Swell potential should be more thoroughly defined during the design level geotechnical investigation in order to evaluate risk. Surface Drainage: Positive drainage should be provided during construction and maintained throughout the life of the proposed residence. Infiltration of water into utility or foundation excavations must be prevented. Planters and other surface features which could retain water in areas adjacent to the building or pavements should be sealed or eliminated. In areas where sidewalks or paving do not immediately adjoin the structure, we recommend that protective slopes be provided with minimum grades of approximately 10 percent for at least 10 feet from perimeter walls. Backfill against footings, exterior walls, and in utility and sprinkler line trenches should be well compacted cohesive soil and free of all construction debris to reduce the possibility of moisture infiltration. Downspouts, roof drains or scuppers should discharge into splash blocks or extensions when the ground surface beneath such features is not protected by exterior slabs or paving. Sprinkler systems should not be installed within 5 feet of foundation walls. Landscaped irrigation adjacent to the foundation system should be minimized or eliminated. Septic System Construction: Subsurface conditions encountered in our test borings consisted of approximately 3% to 12 feet of lean to fat clay with varying amounts of sand overlying sedimentary claystone bedrock. Groundwater was recorded in Boring 1 at a depth 10 ' Preliminary Geotechnical Engineering Report i 9 P Terracon N.C.Ranch—Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 of about 11% feet below the ground surface 1 day after drilling. The other borings remained dry to the depths explored. Preliminary field data indicates percolation rates ranging from about 30 to 480 minutes per inch (mpi). These values indicate that the on site soils have variable percolation characteristics, ranging from good to poor. Weld County and/or State regulations for individual sewage disposal systems (ISDS) require that the following criteria, at a minimum, be met in order to construct standard septic system and leach fields (soil absorption beds): • The depth to bedrock or the maximum seasonal high ground water level must be at least 6 feet below the ground surface in the area of the proposed septic system construction; • Soil percolation rates must be between 5 to 60 minutes per inch (mpi); and • The ground surface slope must not exceed thirty percent Based on the preliminary field test results and data, it appears that septic systems on the site will need to be designed by a registered professional engineer on most, if not all of the lots, due to poor soil percolation characteristics and/or shallow bedrock. Based on the preliminary percolation tests, and assuming a 4 bedroom residence, leach field bed areas could range in size from about 2,000 to 6,000 square feet, or more, in plan view. When final size and location of each residence has been established, design level percolation testing, soil profile evaluation and engineering analysis will be needed on each site in order to determine system type and design criteria. It should be noted that design level testing may reveal conditions significantly different from those found during our preliminary investigation. Pavement Construction: The required total thickness for the pavement structure is dependent primarily upon the foundation soil or subgrade and upon traffic conditions. Results of gradation and plasticity tests on a selected sample indicates that the materials likely to be encountered at street subgrade classify as A-7-6 soils according to the AASHTO classification system. The AASHTO group index of the sample tested was determined to be 32. These soils classify as "CL" according to the Unified Soil Classification System (USCS) methods. Physical property tests indicate that the clay soils at the site have poor to very poor pavement support characteristics. The preliminary pavement thickness presented is based on a minimum EDLA value of 5 for a low volume street serving 9 residential building lots. For planning purposes, we anticipate the pavement section for the private access street would consist of around 3 to 3'/ inches of asphalt over 8 to 11 inches of aggregate base course provided the pavement section is 11 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch—Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 placed on a stable subgrade. We recommend a detailed subgrade investigation and pavement design be conducted prior to construction. Corrosion Protection (Concrete): We measured soluble sulfate concentrations for representative samples of the subsoils which will likely be in contact with structural concrete. The sulfate concentrations measured in the samples varied from 680 to 4,000 ppm. ACI rates the measured concentrations as being a moderate to severe risk of concrete sulfate attack. For severe sulfate exposure, ACI recommends the use of Type V cement (or equivalent) and a maximum water cement ratio of 0.45 for concrete members on and below grade. Foundation concrete should be designed in accordance with the provisions of the ACI Design Manual, Section 318, Chapter 4. GENERAL COMMENTS Terracon should be retained to perform the final subsurface investigation on the project and 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 testing and observation during excavation, grading, foundation and other construction phases of the project. The analyses and preliminary recommendations in this report are based in part upon data obtained from the borings performed at the indicated locations and from other information discussed in this report. This report does not reflect variations which may occur between borings or across the site. The nature and extent of such variations may not become evident until the final subsurface investigation or construction. If variations appear, it will be necessary to reevaluate the preliminary recommendations of this report. The preliminary recommendations presented in this report are intended for planning purposes. A design level geotechnical exploration will be required on each building site in order to design and construct foundations and floor slabs. The scope of services for this project does not include either specifically or by implication any environmental assessment of the site or identification of contaminated or hazardous materials or conditions. If the owner is concerned about the potential for such contamination, other studies should be undertaken. 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. In the event that changes in the nature, design or location of the project outlined in this report are planned, the conclusions and preliminary recommendations contained in 12 Preliminary Geotechnical Engineering Report Terracon N.C.Ranch—Minor Subdivision South Side of Hwy 66 Between CLR and WCR 3 Weld County,Colorado Terracon Project No.22015241 this report shall not be considered valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this report in writing. 13 1 I 1 - Fre rArr Ill&IWAY 66 L ' ' PROXCT • sr: . • 0 ■ oc • • I 1 • I I 3 L . . J N 0 O ) • 1 i P2 • I r ( I VICINITY MAP P-4 NO 5GALC I $ E I I tI r�TB-.., ra4 al P' \\ .P_, / I © a o EX/5r/NS DITCH LCGLND APPROX/Y/Arr LOCATION Or —�L TL5r BORING DR/LLCD ON Z il. NOVCMBCR 15,2001 APPRONMATC LOCATION • Or PCRCOLArcONI1OLL5 ,4O rrrww NO✓LI'IBCR 14,2001 K/MOERLY 5TENCR5ON MINOR 5UODN5ION-N.G.PANG/I 5.5/DC OF 5M41Y66 OETWCCN CLR 8 WO?3 WCLD COUNTY,COLORADO PI&JRP 1..TEST OOP/NS LOCATION PLAN °""�' CW lrerracan 1---�OO- Q��FB 4-24-01 thecae M CJP >P.e re�..w Place 11/16/01 DIAGRAM FOR GCNCRAL CATION ONLY,MD 15 NOT IMINDCD roe CON5R(,GTON PURPO5C5 RI as 5-19-99 Longmont Colorado(0:4521RO CHS 4-22-98 .+M L5yy 303-776-3921Seen 1ft /of/ • LOG OF TEST BORING NO. TB-1 Page 1 of 1 CLIENT • Kimberly Sternerson SITE S. Side of HWY 66 Between CLR & WCR 3 PROJECT Weld County, Colorado N.C. Ranch - Minor Subdivision • SAMPLES TESTS O J a DESCRIPTION m > o 3 wy - z u, U ¢ ¢ < 1- i- - F O¢ a W > ~z ¢w Z zQz USo a 0 w UU z3 fz > o2w WIC o Approx. Surface Elev.: Grade o D D >- w we-a 30 ft— Dow 008 n s TOPSOIL LAYER, Clayey soil with light \vegetation and root penetration. LEAN CLAY, trace sand, light brown, brown, olive brown, very stiff to hard,slightly moist to moist, calcareous. CL CB 26/12 14 118 +8.6/500 5- - CL CB 40/12 14 121 +6.7/1000 10- - 12 CLAYSTONE, olive, grey to dark grey, rust, weathered to hard, moist, moderate to high — plasticity, occasional gypsum. — CB 43/12 18 113 15 CB 50/8 13 121 22970 20 25 - CB 50/6 ' 15 120 Bottom of Test Boring 25 0 z O U Q 2 2 The stratification lines represent the approximate boundary lines - between soil and rock types: in-situ,the transition may be gradual. WATER LEVEL OBSERVATIONS, ft BORING STARTED 11-13-01 EWL WL `ISDry 11/13/01 11.5 11/14/01BOlerracon RGCME55 FOREMANRING CEFII 1DJD cWL ` APPROVED ESW JOB# 22015241 LOG OF TEST BORING NO. TB-2 Page 1 of 1 CLIENT Kimberly Sternerson SITE S. Side of HWY 66 Between CLR & WCR 3 PROJECT Weld County, Colorado N.C. Ranch - Minor Subdivision SAMPLES ! TESTS O J c z tu N O DESCRIPTION 0 0 CO > 3 wN '- z0TT, U _ >- ¢ < V- ZyH 0¢ n d = N W > ¢\ ¢W z zQz U2o < a 0 ca d 0 0 z ; Hz > 0021 w10 w m D > w WO <0 ¢•- z0¢ 3�0 o Approx. Surface Elev.: Grade o D z F- ¢ a s 3 0 o a D U B CO ro • n c TOPSOIL LAYER, Clayey soil with light vegetation and root penetration. LEAN to FAT CLAY, trace sand, brown, dark grey-brown, hard, slightly moist to moist, calcareous. — CL CB 40/12 15 116 +11.0/500 CH 7 s 5— CLAYSTONE, olive, grey, rust, weathered _ to hard, slightly moist to moist, moderate to — _ - high plasticity, occasional gypsum. • — CB 50/9 13 125 +6.6/1000 10- - — 215 — CB 50/8 15 118 Bottom of Test Boring 15 0 0 0 0 U 6 2 2 W The stratification lines represent the approximate boundary lines between soil and rock types: in-situ,the transition may be gradual. WATER LEVEL OBSERVATIONS, ft BORING STARTED 11-13-01 WL F 4 Dry 11/13/01 S Dry 11/14/01 erracon R ME-55 FOREMAN BORING COMPLETED 1 IG o WL DJD zcs co WL APPROVED ESW JOB# 22015241 t LOG OF TEST BORING NO. TB-3 Page 1 of 1+ ^ CLIENT Kimberly Sternerson SITE S. Side of HWY 66 Between CLR & WCR 3 PROJECT Weld County, Colorado N.C. Ranch - Minor Subdivision SAMPLES TESTS O DESCRIPTION m > 3 w N a 0 z or, _ N W ¢O z 2 E w a V¢� cc a a o 2 a 00 z WE- > 0fw w¢� w u) > > W wo ¢O Jr- ZO¢ 3�p o Approx. Surface Elev.: Grade o z F- ¢ 0-a 3 o 00)_ Dc.) y w • n c TOPSOIL LAYER, Clayey soil with light J vegetation and root penetration. CL �/ SANDY LEAN CLAY, brown, light brown, slightly moist, calcareous. 3.s CLAYSTONE, olive, grey, rust, slightly CB 50/11 11 127 +12.6/500 weathered to hard, slightly moist to moist, - moderate to high plasticity, occasional 5 gypsum. CB 50/9 15 120 23420 to y1S1 5 CB 50/9 14 122 +3.4/1000 Bottom of Test Boring z 0 U Q 2 2 W The stratification lines represent the approximate boundary lines ,..c, between soil and rock types: in-situ,the transition may be gradual. WATER LEVEL OBSERVATIONS, ft BORING STARTED 11-13-01 WL 4 Dry 11/13/01 ? Dry 11/14/01 llerracon B CME-55 FOREMAN DJD ORING COMPLETED 1 cr o WL 2 Y WL APPROVED ESW JOB# 22015241, LOG OF TEST BORING NO. TB-4 Page 1 of 1 ^ CLIENT Kimberly Sternerson SITE S. Side of HWY 66 Between CLR & WCR 3 PROJECT Weld County, Colorado N.C. Ranch - Minor Subdivision SAMPLES TESTS C7 J z Lure' Q -J DESCRIPTION O m > Q 3 wy ¢ zcW7— ¢ ¢ ` w ¢ mY,z �— mow~rzo 49 le CL circa ¢ a U o_ QO Luc', I--z > �M w¢O co Approx. Surface Elev.: Grade w (I) D >- w w o <O ¢ ZO1- 3 0 PPo z r ¢ CL 3Q O C DOct CO 9 n s TOPSOIL LAYER, Clayey soil with light vegetation and root penetration. LEAN CLAY with SAND, brown, beige, hard, dry to slightly moist, calcareous, with trace fine gravel. . CL CB 42/12 16 105 +6.1/500 s 5 CLAYSTONE, olive, grey to dark grey, rust, weathered to very hard, slightly moist to moist, moderate to high plasticity, occasional gypsum. CB 50/12 11 124 +7.7/1000 10 CB 50/9 16 118 +3.2/1750 15 ■.CB- 50/6 13 124 22920 20 Yee 25 CB 50/5 14 119 Bottom of Test Boring 25 00H 2 2 0 U 4 The stratification lines represent the approximate boundary lines between soil and rock types: in-situ. the transition may be gradual. WATER LEVEL OBSERVATF„.NS, ft BORING STARTED 11-13-01 WL WL is Dry 11/13/01 s Dry 11/14/01 llerracon RIG CME-55 FOREMAN DJD COMPLETED 11-13-01 I 1 OD WL IAPPROVED JOB# 22015241 16' I I 14 12 10- J w 8 - 6 z 0 4 O J 0 z 2 O 0 4 -2 -4 _ 0.1 1 10 100 APPLIED PRESSURE,ksf N Specimen Identification Classification ' Yd, pcf WC,% • TB-1 3.0ft LEAN CLAY(CL) 118 14 0 Notes: a c7 �1 N N SWELL/CONSOLIDATION TEST Project: N.C. Ranch - Minor Subdivision ir erra Site: S. Side of HWY 66 Between CLR & WCR 3 Weld County, Colorado �O� Job #: 22015241 Date: 11-20-01 16 r 14 12 - - 10 - -J LL! U 8 6 _ I z O 4 I a J O U 2 OS + l `� -2 -4 0.1 1 10 100 APPLIED PRESSURE. ksf Specimen Identification Classification Yd, pcf WC,% • TB-1 8.0ft Lean Clay(CL) 121 14 z 0 a Notes: G CS N ice\ Y] SWELUCONSOLIDATION TEST Project: N.C. Ranch - Minor Subdivision N iierracon Site: S. Side of HWY 66 Between CLR & WCR 3 Weld County, Colorado Job#: 22015241 , Date: 11-20-01 16 14 12 _ J 10 J W U) S , . 6 0 4 _ I O J O UJ Z 2 O L U ♦ -2- -4 0.1 1 10 100 APPLIED PRESSURE,ksf Specimen Identification Classification Yd, pcf WC,% • TB-2 3.0ft Lean to Fat Clay, trace Sand (CL-CH)d 1 116 15 a Notes: c7 N SWELL/CONSOLIDATION TEST N Project: N.C. Ranch - Minor Subdivision 7 r err ac Site: S. Side of HWY 66 Between CLR & WCR 3 Weld County, Colorado O� Job#: 22015241 Date: 11-20-01 16 I II 14 I � l 12 , 10 -J 8 8.9 } 6- z a 4 - a a J O 2 0♦ _ -2 -4 0.1 1 10 100 APPLIED PRESSURE,ksf Specimen Identification Classification Yd, pcf WC,% • TB-2 8.0f Claystone 125 13 Notes: 2 a c7 = SWELUCONSOLIDATION TEST Project: N.C. Ranch - Minor Subdivision 1 rerraco Site: S. Side of HWY 66 Between CLR & WCR 3 Weld County, Colorado Job#: 22015241 Date: 11-20-01 16 • I I ' 14 I I II 12 10 w L 8 6 a 4 2 0♦ -2 -4 0.1 1 10 100 APPLIED PRESSURE, ksf Specimen identification Classification 7a, pcf WC,% • TB-3 3.0ft Claystone 127 11 z 0 a Notes: W r a c� v N SWELL/CONSOLIDATION TEST Project: N.C. Ranch - Minor Subdivision ir err acon Site: S. Side of HWY 66 Between CLR & WCR 3 Weld County, Colorado Job #: 22015241 Date: 11-20-01 16 I � 14 12 - - 10- - -J W (I) 8 6 z o 4 I O 2- -2 -4 0.1 1 10 100 APPLIED PRESSURE, ksf Specimen Identification Classification Yd, pcf WC,% • TB-3 14.0it Claystone 122 14 z 0 a Notes: a ,r+ SWELL/CONSOLIDATION TEST Project: N.C. Ranch -Minor Subdivision lierracon Site: S. Side of HWY 66 Between CLR & WCR 3 Weld County, Colorado o Job #: 22015241 Date: 11-20-01 10 I 8 ' I 6 -- 4 - Lc/j) 2 z o -2 0 ...1 U, ^+ p -4 -6 -8 -10 0.1 1 10 _ 100 APPLIED PRESSURE,ksf Specimen Identification Classification Yd, pcf WC,% • TB-4 3.0ft Lean Clay with Sand (CL) 105 16 0 Notes: c.1 a SWELL/CONSOLIDATION TEST Project: N.C. Ranch -Minor Subdivision 1 ferracon Site: S. Side of HWY 66 Between CLR & WCR 3 Weld County, Colorado Job #: 22015241 Date: 11-20-01 16 I I I 14 I i 1 . 12 4 t J 10 W U) 8 - - 6 Z g 4 0 J O Z 2 O O • • • • -2 -4 0.1 1 10 100 APPLIED PRESSURE, ksf Specimen Identification Classification Yd, pcf WC,% TB-4 8.0ft Claystone 124 11 Notes: cc R Lel SWELL/CONSOLIDATION TEST Project: N.C. Ranch - Minor Subdivision 1 ierracon Site: S. Side of HWY 66 Between CLR & WCR 3 Weld County, Colorado 3 Job #: 22015241 Date: 11-20-01 161 E 14 • ! I r 12 I 10 J W 8 6 z O 4 cn 2 a -2 -4 0.1 1 10 100 APPLIED PRESSURE,ksf Specimen Identification Classification Yd, pcf WC,% • TB-4 14.0ft Claystone 118 16 0 Notes: ct a' SWELUCONSOLIDATION TEST Project: N.C. Ranch - Minor Subdivision lierracon Site: S Side of HWY 66 Between CLR & WCR 3 Weld County, Colorado o Job #: 22015241 Date: 11-20-01 U.S.SIEVE OPENING IN INCHES o.S.SIEVE NUMBERS HYDROMETER 8 4 3 2 1.5 1 3,4 1/23,8 3 6 610 1416 „ 30 a 50 60 100..0200 100 I I IIT I I � f"� - I 90 85 80 • 75 70 65 w• 60 3 I Y 55 re z50 LL Z 45 W ¢ 40 35 30 25 20 15 - 10 5 0 100 10 1 0.1 0.01 0.001 GRAIN SIZE IN MILLIMETERS COBBLES GRAVEL SAND SILT OR CLAY coarse fine coarse I medium fine Specimen Identification Classification LL PL PI Cc Cu • TB-1 3.0ft LEAN CLAY(CL) 48 17 31 m TB-3 8.0ft Claystone 51 20 31 Specimen Identification D100 D60 D30 D10 %Gravel %Sand %Silt %Clay • TB-1 3.0ft 4.75 0.0 3.1 96.9 o I TB-3 8.0ft 4.75 0.0 0.4 99.6 e cc w C. 0 GRAIN SIZE DISTRIBUTION/SOIL CLASSIFICATION w Project: N.C. Ranch - Minor Subdivision lierr acon Site: S. Side of HWY 66 Between CLR & WCR 3 Weld County, Colorado Job #: 22015241 O Date: 11-20-01 GENERAL NOTES DRILLING &SAMPLING SYMBOLS: SS: Split Spoon- 1-3/8" I.D., 2" O.D., unless otherwise noted HS: Hollow Stem Auger ST: Thin-Walled Tube-2Y:" I.D., unless otherwise noted PA: Power Auger RS: Ring Sampler-2.42" I.D., 3" O.D., unless otherwise noted HA: Hand Auger CB: California Barrel — 1.92" I.D., 2.5" O.D. RB: Rock Bit BS: Bulk Sample or Auger Sample WB: Wash Boring or Mud Rotary The number of blows required to advance a standard 2-inch O.D. split-spoon sampler (SS) the last 12 inches of the total 18-inch penetration with a 140-pound hammer falling 30 inches is considered the "Standard Penetration" or"N-value". WATER LEVEL MEASUREMENT SYMBOLS: WL: Water Level WS: While Sampling WCI: Wet Cave in WD: While Drilling DCI: Dry Cave in BCR: Before Casing Removal AB: After Boring ACR: After Casing Removal Water levels indicated on the boring logs are the levels measured in the borings at the times indicated. Groundwater levels at other times and other locations across the site could vary. In pervious soils, the indicated levels may reflect the location of groundwater. In low permeability soils. the accurate determination of groundwater levels may not be possible with only short- term observations. DESCRIPTIVE SOIL CLASSIFICATION: Soil classification is based on the Unified Classification System. Coarse Grained Soils have more than 50% of their dry weight retained on a #200 sieve; their principal descriptors are: boulders, cobbles, gravel or sand. Fine Grained Soils have less than 50% of their dry weight retained on a#200 sieve; they are principally 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 in-place relative density and fine-grained soils on the basis of their consistency. CONSISTENCY OF FINE-GRAINED SOILS RELATIVE DENSITY OF COARSE-GRAINED SOILS Standard Unconfined Penetration or Standard Penetration Compressive N-value(SS) or N-value(SS) Strength, Qu, psf Blows/Ft. Consistency Blows/Ft. Relative Density < 500 <2 Very Soft 0—3 Very Loose 500 - 1,000 2-3 Soft 4-9 Loose 1,001 - 2,000 4-6 Medium Stiff 10-29 Medium Dense 2,001 - 4,000 7-12 Stiff 30-49 Dense 4,001 - 8,000 13-26 Very Stiff 50+ Very Dense 8,000+ 26+ Hard RELATIVE PROPORTIONS OF SAND AND GRAVEL GRAIN SIZE TERMINOLOGY Descriptive Term(s) of other Percent of Major Component constituents Dry Weight of Sample Particle Size Trace < 15 Boulders Over 12 in. (300mm) With 15—29 Cobbles 12 in. to 3 in. (300mm to 75 mm) Modifier > 30 Gravel 3 in. to#4 sieve(75mm to 4.75 mm) Sand #4 to#200 sieve (4.75mm to RELATIVE PROPORTIONS OF FINES Silt or Clay 0.075mm) Passing#200 Sieve (0.075mm) Descriptive Term(s)of other Percent of PLASTICITY DESCRIPTION constituents Dry Weight Term Plasticity Index Trace < 5 Non-plastic 0 `0"-- With 5- 12 Low 1-10 Modifiers > 12 Medium 11-30 High 30+ lierracon • UNIFIED SOIL CLASSIFICATION SYSTEM Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests Soil Classification e.•'•' Group Symbol Group Name' Coarse Grained Soils Gravels Clean Gravels Cu≥4 and 1 ≤Cc≤3E GW Well-graded gravelF More than 50% retained More than 50%of coarse Less than 5%fines° Cu<4 and/or 1 >Cc>3° GP Poorl fraction retained on y graded gravel` on No. 200 sieve No.4 sieve Gravels with Fines More Fines classify as ML or MH GM Silty gravelF G" than 12%foes= Fines classify as CL or CH FGe GC Clayey gravel Sands Clean Sands Cu≥6 and 1 e Cc≤3s SW Well-graded sand 50%or more of coarse Less than 5%fines° Cu<6 and/or 1 >Cc>3E SP Pood fraction passes y graded sand No.4 sieve Sands with Fines Fines classify as ML or MH SM Silty sandGH' More than 12%finest Fines Classify as CL or CH SC Clayey sand°° Fine-Grained Soils Silts and Clays inorganic PI >7 and plots on or above"A"line' CL Lean clay'°ua 50%or more passes the Liquid limit less than 50 PI 4 plots below"A"lined ML Serallo.200 sieve < or organic Liquid limit-oven dried Organic clay'-u"" <0.75 OL Liquid limit-not dried Organic silt"""° Silts and Clays inorganic PI plats on or above"A"line CH Fat clayRL" Liquid limit 50 or more PI lots below"A"line MH Elastic Sea organic Liquid limit-oven dried Organic clayK.MF 0.75 OH Liquid limit-not dried Organic silt1t t0 Highly organic soils Primarily organic matter,dark in color,and organic odor PT Peat "Based on the material passing the 3-in.(75-mm)sieve "If fines are organic,add"with organic fines"to group name. 'If field sample contained cobbles or boulders,or both,add'with cobbles or ' If soil contains≥15%gravel,add"with gravel"to group name. boulders,or both"to group name. 'If Atterberg limits plot in shaded area,soil is a CL-ML,silty clay. '""°Gravels with 5 to 12%fines require dual symbols: GW-GM well-graded K If soil contains 15 to 29%plus No.200,add"with sand"or"with gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorly graded gravel,"whichever is predominant. gravel with silt, GP-GC poorly graded gravel with clay. I-If soil contains a 30%plus No.200 predominantly sand,add"sandy" °S ands with 5 to 12%fines require dual symbols: SW-SM well-graded sand to group name. with silt,SW-SC well-graded sand with clay,SP-SM poorly graded sand " with silt,SP-SC poorly graded sand with clay If soil contains≥30%plus No.200,predominantly gravel,add "gravelly'to group name. E Cu=Deo/D,° Cc= (D'°) • "PI≥4 and plots on or above"A"line. Dm X Deo °PI<4 or plots below"A"line. F If soil contains≥15%sand,add"with sand"to group name. F PI plots on or above"A"line. °If fines classify as CL-ML,use dual symbol GC-GM,or SC-SM. °PI plots below"A"line. 60 7 For classification of fine-grained soils and fine-grained fraction 50 Hof coarse-grained soils .gee • e \, , _ �� Equation of"A"-line ,S,r ,.p a Horizontal at PI=4 to LL=25.5. X 40 then PI=0.73(LL-20) des IL O1 p U"Equation of" -line Z Vertical at LL=16 to PI=7, G� >- 30 -'' then P1=0.9(LL-8) 42/ U I & p cn 20 ' Go o MH or OH 77 10 = 7 'L CL•ML ML or 4 '- 0 0 10 16 20 30 40 50 60 70 80 90 100 110 LIQUID LIMIT(LL) lierracon _ Form 111-6/98 ROCK CLASSIFICATION (Based on ASTM C-294) Sedimentary Rocks Sedimentary rocks are stratified materials laid down by water or wind. The sediments may be composed of particles of pre-existing rocks derived by mechanical weathering, evaporation or by chemical or organic origin. The sediments are usually indurated by cementation or compaction. Chert Very fine-grained siliceous rock composed of micro-crystalline or crypto- crystalline quartz, chalcedony or opal. Chert is various colored, porous to dense, hard and has a conchoidal to splintery fracture. Claystone Fine-grained rock composed of or derived by erosion of silts and clays or any rock containing clay. Soft massive; gray, black, brown, reddish or green and may contain carbonate minerals. Conglomerate Rock consisting of a considerable amount of rounded gravel, sand and cobbles with or without interstitial or cementing material. The cementing or interstitial material may be quartz, opal, calcite, dolomite, clay, iron oxides or other materials. Dolomite A fine-grained carbonate rock consisting of the mineral dolomite ICaMg (CO3121. May contain noncarbonate impurities such as quartz, chert, clay minerals, organic matter, gypsum and sulfides. Reacts with hydrochloric acid (HCL). Limestone A fine-grained carbonate rock consisting of the mineral calcite (CaCo3). May contain noncarbonate impurities such as quartz, chert, clay minerals, organic matter, gypsum and sulfides. Reacts with hydrochloric acid (HCL). Sandstone Rock consisting of particles of sand with or without interstitial and cementing materials. The cementing or interstitial material may be quartz, opal, calcite, dolomite, clay, iron oxides or other material. Shale Fine-grained rock composed of, or derived by erosion of silts and clays or any rock containing clay. Shale is hard, platy, or fissile may be gray, black, reddish or green and may contain some carbonate minerals (calcareous shale). Siltstone Fine grained rock composed of, or derived by erosion of silts or rock containing silt. Siltstones consist predominantly of silt sized particles (0.0625 to 0.002 mm in diameter) and are intermediate rocks between claystones and sandstones, may be gray, black, brown, reddish or green and may contain carbonate minerals. lierracon Hello