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Home My WebLink AboutSubsoil Study for Foundation Design 05.03.17H.PVKUMAR 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Far (970) 945-8454 Email: hpkglenwood@kumarusa.com Geotechnical Engineering I Engineedng Geology Materlals Testing I Environmental Office Loætions: Parke¡ Glenwood Springs, and Silverthorne, Colorado SUBSOIL STUDY FOR FOUNDÄTION DESIGN PROPOSED RESIDENCE PARCEL 217901100528 TBD COUNTY ROAD 2I4 GARFIELD COUNTY, COLORADO JOB NO. t7-7-202 MAY 3,20L7 PREPARED FOR: CHET STICKLER 526 EAGLE NEST DRIVE SILT, COLORADO 81652 @ TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY............ PROPOSED CONSTRUCTION SITE CONDITIONS FIELD EXPLORATION ........ SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS......... FLOOR SLABS UNDERDRAIN SYSTEM SURFACE DRAINAGE ... LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 AND 5 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS 1 -7 - -1- 1 2- -3- 5 H-PtKUMAR Project Na.17-7-202 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study t'or a proposed residence to be located on parcel number 21790L100528, TBD County Road Z| ,Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to Chet Sticklel dated Febru ary 22,2017 . A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the fîeld exploration were tested in the laborafory to determine their classification, compressibility or swell ancl other engineering characteristics. The results of the field exploration and laboratory testing were analyzed to develop recommendations for foundation types, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conclusions, design rccommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION Development plans were conceptual ât the time of our stlldy. The proposed residence will be a one story wood frame structure above a crawlspace and with an attached garage. Garage floor will be slab-on-grade. Grading for the structure is assumed to be relatively minor with cut depths between about 2 to 4 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITIONS The property is 5.334 acres and located along the south side of County Road 214 (Peach Valley Road) across from Cedar Hills subdivision. The vacant site is currently used as inigated pasture H-P*KUMAR Project No. 17-7-242 -2- land. Vegetation consists of sparse grass and weeds. The ground surface is relatively flat with a slight slope down to the south. An irigation ditch and ranch road parallel the rear property line. FIELD EXPLORATION The field exploration for the project was conducted on March 20,2077. Two exploratory borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions. The borings were advanced with 4 inch diameter continuous flight augers powered by a truck- mounted CME-458 drill rig. The borings were logged by a representative of H-P/Kumar. Samples of the subsoils were taken with a 2inchl.D. spoon sampler. The sampler was driven into the subsoils at various depths with blows from a 140 pound hammer falling 30 inehes. This test is similar to the standard penetration test described by ASTM Method D-1586. The penetration rcsistance values ale an indication of the relative density or consistency of the subsoils. Depths at which the samples were taken and the penetration resistance values arc shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered ât the site are shown on Figure 2. The subsoils consist of about one foot of topsoil overlying medium dense, silty to very silty sand with occasional sandy clay layers. Laboratory testíng performed on samples obtained from the borings included natural moisture content, density and percent finer then sand size gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed drive samples, presented on Figures 4 and 5, typically indicate low to moderate compressibility under conditions of loading and wetting and minor hydro-compression potential. A sample of sandy silty clay from Boring I at 20 feet showed a low expansion potential when wetted. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist. H.P\KUMAR Project No. 17-7-202 -3- FOUNDATION BEARING CONDITIONS The silty sand soils encountered in the boring possess low bearing capacity and typically tend to compress when they become wetted. Lightly loaded spread footings should be feasible for foundation support of the residence with some risk of settlement. The risk of settlement is primarily if the bearing soils were to become wetted and precautions should be taken to prevent wetting. Sources of wetting include excessive irrigation near the foundation, poor surface drainage adjacent to foundation walls and utility line leaks. Expansive clay soils encountered at bearing level in the excavation should be removed. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the naturc of the proposed construction, we recommend the building be founded with spread footings bearing on the natural granular soils below topsoil and expansive clay soils. The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed on the undistr¡rbed natural granular soils should be designed for an allowable bearing presslrre of 1,500 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about I inch or less. There could be additional settlement if the bearing soils become wetted of about rhto I inch depending on the depth and extent of the wetting. 2) The footings should have a minimum width of 18 inches for continuous walls and 2 feet for isolated pads. 3) Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this aÍea. 4) Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet, q structures should also be designed to resist a H.PùKUMAR Founrlafion walls actins as Project No.17-7-202 4 lateral earth pressure corresponding to an equivalent fluid unit weight of at least 50 pcf. The topsoil, expansive clay soils and any loose or disturbed soils should be removed and the footing bearing level extended down to the natural granular soils. The exposed soils in footing area should then be moistened and compacted. A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction. The silty sand soils are compressible when wetted which could result in some slab settlement and distress if they become wetted. Expansive clay soils should be removed and can be replaced with compacted structural fill. To reduce the effects of some differential movement, floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4 inch layer of free-draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2 inch aggregate with at least 50Vo retained on the No. 4 sieve and less than 27o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95Vo of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site granular soils devoid ofvegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our expericnce in the area that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. V/e recommend below-grade construction, such as retaining walls and basement areas, be protected from wetting and hydrost¿rtic pressure buildup by an underdrain system. 5) 6) H-P*KUMAR Project Na.17-7-2Q2 5 The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free-draining granular material. The drain should be placed at each level of excavaticn and at least I foot below lowest acljacent finish gracle and sloped at a minimnm l9¿ to a suitable gravity outlet or sump and pump. Free-draining granular material used in the underdrain system should contain less than 2Vo passing the No. 200 sieve, less than 507o passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least 1/z feet deep and be covered by a filter fabric such as Mirafi 140N. SURFACE DRAINAGE Positive surface drainage is a very important aspect of the project to prevent wetting of the bearing soils. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation ofthe foundation excavations and underslab areas should be avoided during construction. 2) F.xterior backf,ll should be adjusted to near optimum moisture and compacted to at least 95Vo of the maximum standard Proctor density in pavement and slab areas and to at least 9AVo of the maximum standard Proctor density in landscape areas. 3) The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first l0 feet in paved areas. Free-draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irigation shoi¡ld be located at least 10 feet from foundation walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building caused by imigation. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this tine. 'We make no warranty either express or implied. H.P*KUMAR Project No. 17-7-2Oz -6- The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings drilled at the locations indicated on Figure 1, the.proposed type of construction and our experience in the area. Our services do not include determining the presence, prevention or possibility of mold or other biological contaminants (MOBC) developing in the future' If the client is concerned about MOBC, then a professional in this special field of practice should be consulted. Our findings include interpolation and extrapolation of the subsurface conditions identified at the exploratory borings and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear different from those described in this report, we should be notified so that re-evaluation of the recommendations may be made. This report has been prepared for the exclusive use by our client for design purposes. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and field services during construction to review and monitor the implementation of our recommendations, and to verify that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. We recommend on-site observation ofexcavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, H.P\ KUMAR Louis E. Eller Reviewed by: Steven L. Pawlak, P LEElksw H.P*KUMAR Project No. 17-7-202 BORING Ia o srNcn MARK: GROUND AT CENTER POST; ELEV. : 100.0" ASSUMED ìI a 2BORING I \tI \IIL II \II \II \ tI \ It \ II \II \ *oÞó , t I \II \ q rrlvclI ¿( -g I \It \I \II \ I ooc,z -.11 ßovo F,J Þ I APPROXIMATE SCALE-FEET 17-7*202 H-PryKUMAR LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING 1 EL. 97.5'BORING 2 EL. gg.5' 0 o 12/12 WC=5.8 DD=98 -200=45 1o/ 12 5 512/12 WC=5.3 DD=95 1s/ 12 WC=5.1 DD=1 09 10 1020/12 WC=5.2 DD=1 I 5 20/12 WC=5.3 DD=l 1 5 t- L¡¡ l¡Jt! IxFo-t¡,o 15 15 t-.-'L¡lLI l! I 27/12 25/12 WC=7.6 DD=1 1 3 -200=63 20 2040/ 12 WC=4.E ÐÐ=124 30/12 25 2348/12 41/12 30 30 17-7-2A2 H-PryKUMAR LOGS OF TXPLORATORY SORINGS ri1. 2 ¡ TEGFND TOPSoIL; ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, DARK BROWN D4sruo (sv); Ll SLTGHTLY M SILTY TO VERY SILTY, OCCASIONÀL SANDY SILTY CLAY LAYERS, MEDIUM DTNSE, otsT, BRowN. F RELATIVELY UNOISTURBED DRIVE SAMPLE; 2-INCH l.D. CALIFORNIA LINER SAMPLE. ^^r.. DRIVE SAMPTE BLOW COUN'|. INDICATES THAT 20 BLOWS OF À 140-POUND HAMMER "/ '' FÂLLING J0 tNcHEs wERE REQUIRED To DRrvE THE cALrFoRNt,A SAMpLER i2 rNcHEs NOTES I. THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 20, 2A17 WITH A 4-INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASUREÐ BY HAND LEVEL AND REFER TO THE BENCHMARK ON TIC. 1. 4 THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON Tt{E EXPLORATORY BORING LOGS REPRESENT THE APPROX|MATE BOUNÐARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUÀ1. 6. GROUNDWATER WAS NOT ËNCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING. 7, LABORATORY TEST RESULTS: Wc - WATTR C0NTENT (%) (AsrM O 2216); DD = DRY DENSITY (PCf) (ASTM D 2216); -2Q0= PERCENÍAGE PASSING NO. 200 SIEVE (ASTM D 1140) 17-7-202 H-PryKUMAR LEGTND AND NOTTS Fig. 3 , I ¡ SAMPLE OF: Cloyey Silty Sond FROM:Borlngl@5' WC = 5.3 %, DÐ = 95 pcf ii --* ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I t I : 'I : t i I :1It i; i : I : a 0 ^ -t )-¿l¡l =Ø l-s zotr I-t)olnzoo_5 -6 -7 -6 t0 17 -7 -202 H-PryKUMAR SWELL-CONSOLIDATION TEST RESULT Fí9. 4 2 1 0 -1 -2 I 0 -1 -2 -3 -4 -5 ñ )J LJ ln I z.otr =o tJ1zo(J J)td =(n I zo F o =o an ou t.0 '10 SAMPLE OF: Sondy Sìlty Cloy FROM:Boringle.20' WC = 4.8 %, ùÐ = 124 pcl , .. ¡ : t 1 1 : .i I I 1 1 I t : I : I:, It .: 1i )t 'i "" ; :l :1 'I a il I I i l 1 ì I : I l I 1 1 : ) I I I EXPANSION UNDER CONSTANT PRESSURE UPON WETÍING t -1 ': -' . ì -. -t I I I I I i a t I il )l SAMPLE OF: Silty Cloyey Sond FROM: Boring 2 @ 10' WC = 5.3 %, DD - 115 pcf ADDIÏIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING SWELL_CONSOLIDATION TEST RESULTS Fig. 517 -7 -202 H.PryKUMAR H-PtKUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProjectNo. 17-7-202SOIL TYPEVery Silty SandClayey Silty SandSilty SandSandy Silty ClaySilty SandSilty Clayey SandVery Sandy ClayUNCONFINEDCOÍ'TPRESSIVESTRENGTI{{PSFìATTERBERG LIMITSPLASTICINDEX(%lLIQUIDLIMlTIo/"1PERCENTPASSINGNO.200SIEVE4563GRADATIONSAND(%tGRAVEL$tNATURALDRYDENSITYlocfl9895113124109115l13NATURALi,IOISTURECO}.TTENTBORINGDEPTH5.8s?5.24.85I5.37.62t/z5I02051015I2