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Home My WebLink AboutSubsoil Study for Foundation Design 08.31.18H.PVKUMAR Geoþchnical Engineedng I Englneedng Geology Materials Testing I Envlrcnmental 5020 County Road 154 Glenwood Springs, CO 81001 Phone: (970) 94S-79S8 Fax (970) 945-84s4 Email: hpkglenwood@kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit Count¡ Colorado ST]BSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 34, SPRINGRIDGE RESERVE IIIDDEN VALLEY DRIVE GARFIELD COUNTY, COLORADO JOB NO. 18-7-4sr aUGUST 31,2018 PREPARED FOR: FLORES CONSTRUCTION ATTN: LARRY FLORES 3694 VALLEY VIEW ROAD GLENWOOD SPRINGS, COLORADO 81601 @ TABI,E OF CONTIìNTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION .... SITE CONDITIONS FIELD EXPTORATION ....... SUBSURFACE CONDITIONS DESIGN RECOMMENDATIONS ................ .... FOUNDATIONS FOUNDATION AND RETAINING WALLS 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. I -2- I aJ aJ 4 5 6 6 /: -7 H-PVKUMAR Project No. 18-7-451 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 34, Springridge Reserve, Hidden Valley Drive, Garfîeld 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 general accordance with our agreement for geotechnical engineering services to Flores Construction dated July 3,2018. Hepworth-Pawlak Geotechnical previously performed a preliminary geotechnical study for the subdivision and reported the findings in a report dated February 26,2001, Job No. l}l 126 and updated the srudy in a report dated June 22,2004. A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classification, compressibility or swell and 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 rep.ort summarizes the data obtained during this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION Building plans were not available at the time of olrr study. In general, the proposed residence will be a two-story wood frame structure with an attached garage and slab-on-grade floors and located within the building envelope shown on Figure 1. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 6 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. H-PVKUMAR Project No. 18-7-451 a SITE CONDITIONS The property was vacant at the time of our field exploration. The site is vegetated with grass, weeds and sage brush with juniper trees above the general building area. The ground surface in the general building area slopes gently to moderately down to the northeast at about l0 ta l2Vo. The grade steepens slightly in the upper lot area at about líVo, see Figure l. Maroon Formation sandstone is exposed on the hillside to the west of the lot. FIELD EXPLORATION The lreld exploration for the project was conducted on luly 27,2018. Two exploratory borings were drilled at the locations shown on Figure 1 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 l% inch and 2-inch I.D. spoon samplers. The samplers were driven into the subsurfape materjals at various depths with blows from a 140 pound hammer falling 30 inches. This test is similar to the standard penetration test described by ASTM Method D-1586. The penetration resistance values are an indication of the relative density or consistency of the subsoils and hardness of the bedrock. Depths at which the samples were taken and the penetration resistance values are shown on the Logs of Exploratory Borings, Figure 2. The samples were retLlrned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils were variable and below about 1 to 3 feet of topsoil consist of sandy silt and clay in Boring i overlying sandstone bedrock at a depth ofabout I}Vzfeet. In Boring 2, about 7 feet of sandy silt and clay was encountered above silty sand soils with sandstone bedrock at a depth of about 17 feet. The bedrock became very hard with depth and practical drilling refusal was encountered in the formation at Boring L H.PVKUMAR Project No. 18-7-451 -3- Laboratory testing perfonned on sarnples obtained from the borings included natural moisturc content and density and finer than sand size gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed drive samples of the soils, presented on Figures 4 and 5, generally indicate low to moderate compressibility under light loading and a low collapse potential (settlement under constant load) when wetted. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling or when checked several weeks later and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The top of bedrock slopes down to the east and may be encountered in the upper part of the building excavation and transition to sand, silt and clay in the remaining areas of the excavation. The sand, silt and clay soils are of variable compressibility potential and could tend to settle especially when they become wetted. A shallow foundation placed on the sand, silt and clay soils will have a risk of settlement if the soils become wetted and care should be taken in the surface and subsurface clrainage around the house to keep the bearing soils dry. It will be critical to the long telm performance of the structure that the recommendations for surface grading and sr¡bSurface drainage contained in this report be followed. Presented below ale recommendations for shallow spread footings with a risk of settlement. A low settlement risk foundation support can be achieved by extending the bearing down into the underlying bedrock such as with straight-shaft drilled piers or helical piers. If a deep foundation is desired, we should be contacted for additional recommendations. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, the building can be founded with spread footings bearing on the natural soils below topsoilpp{þlhlgyqelqgggplq the risk of settlement and potenrial building distress H-PVKUMAR Project No. 18-7-451 4 The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural soils should be designed for an allowable bearing pressure of 1,200 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. Additional differential settlement could be on the order of r/zto I inch for a limited wetted depth of around 10 feet below the footings. 2) The footings should have a minimnm width of 20 inches for continuous walls ancl 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 area. 4) Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 14 feet. Foundation walls acting as retaining structnres should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) The topsoil and any loose or disturbed soils should be rcmovecl and the footing bearing level extended clown to the firm natural soils. The exposed soils in footing area should then be moistened and compacted. 6) A representative of the geotechnical engineer shonlcl observe all footing excavations plior to concrete placement to eyaluate bearing conditions. FOUNDATION AND RETAINING V/ALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of defiection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are separate from the residence and can bs expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 45 pcf for backfill consisting of the on-site soils. H-PVKUIVIAR Project No. 18-7-451 -5- All foundation and retaining structlrres should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the iateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90Vo of the maximum standard Proctor density at near optimum moisture content. Backfill placed in pavement and walkway areas should be compacted to at least 95Va of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.40. Passive pressurt of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 325 pcf. The coefficient of friction and passive prcssure values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to limit the strain which will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be compacted to at least 95Vo of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade construction. There could be differential settlement potential from wetting of the bearing soils similar to that described above for footings. To reduce the effects of some differential movement, floor slabs should be separated from all bearing wails 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 H-PVKUMAR Project No. 18-7-45'! -6 reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4-inch layer of relatively well graded sand and gravel such as road base should be placed beneath slabs fo¡ support. This material should consist of minus 2-inch aggregate with at least SOVo rctained on the No. 4 sieve and less than 12Vo 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 soils devoid of vegetation, topsoil and oversized (plus 6 inch) rock. UNDERDRAIN SYSTEM Although free water \ryas not encountered during our exploration, it has been our experience in the area and where there are clay soils that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. We recommend below-grade construction, such as retaining walls, be protected from wetting and hydrostatic pressure buildup by an underdrain system. Where installed, the drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free-draining granuiar material. The drain should be placed at each level ofexcavation and at least I foot below lowest adjacent finish grade and sloped at a.minimu m LVo to a sllitable gravity outlet. Free-draining granular matelial used in the underdrain system should contain less than 2Vo passingthe 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 lVz feet deep. An impewious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils unless the bearing material is bedrock or non-moisture sensitive soil. SURFACE DRAINAGE Proper surface grading and drainage will be critical to limiting subsurface wetting below the building. 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. H-P*KUMAR Project No. 18-7-451 2)Exterior backfill 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. The ground surface sunounding 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 10 feet in paved areas. Free-draining wall backfîll should be covered with filter fabric and capped with about 2 feet of the on-site soils to reduce surface water infiltration. Roof downspouts and drains should discharge well beyond the limits of all backfill. Landscaping which requires regular heavy inigation should 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 inigation. 3) 4) s) LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings dLilled at the locations indicated on Figure l, 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 info¡mation. As the project evolves, we H-PVKUMAR Project No. 18-7-451 -8- 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 of excavations and foundation bearing strata and testing of strúctural fill by a representative of the geotechnical engineer. Respectfully Submitted, H-P+KUMAR Steven L. Pawlak, Reviewed by: Daniel E. Hardin, P.E. SLPlkac 1 S3?3 H-PVKUMAR Project No. 18-7-451 1 Lot 32 1 t \sr'te\EIev. =à\ Y- 5'1 9'18' 1600.ö6 148.67' 3 S 22"37',59" E\ 148.62' Eleclric T¡ Loi 36 D 1"42 51" R 1600.66', L 47.89 c8 s 26"O9',O5" E cH 47.89', ivorEs 1.) D.4TE OFSURyEy WAS JULY 17, 2018. Lot 34 TBD Valleg View Rqad APPROXIMATE SCALE-FEET 18-7 -451 H-PVKUMAR LOCAÏION OF EXPLORATORY BORINGS Fig. 1 i I BORING 1 EL. 6465' BORING 2 EL. 6462' 0 o so/12 WC=6.5 DD=98 -200=36 26/ 12 5 528/ 12 WC=6.0 DD= 1 03 18/12 WC=6.9 DD=92 10 l050/4 2s/ 12 WC=5.9 DD=1 07 -200=53 FLJIJ LL I-t- TL t¡Jô 15 50/ 1 15 t-L!LIL- IT F-o- LJô 24/12 \NC=4.2 DD= 1 06 -2OO=25 20 20so/3 25 t< so/o 30 30 18-7 -451 H-PryKUMAR LOGS OF EXPLORATORY BORINGS Fíg. 2 E LEGEND N TOPSOIu SANDY SILT AND CLAY, SLIGHTLY MOIST, DARK BROWN SILT AND CLAY (ML_CL); SANOY TO VERY SANDY, ScATTERED GRAVEL, SLIGHTLY MoIsT, RED. F y-tlllg.qqD 'ANDST.NE; F'NE To MEDT'M .RATNED, HARD, sLrcHTLy Morsr, RED, MARooN Frl FoRMATtoN. SIHO (SU): SILTY, FINE TO MEDIUM GRAINED, MEDIUM DENSE, SUCHTIÍ MOIST, RED. F:ffil ¡üä]i{ Èi.ìi+.ìr.it F I SANDSTONE BEDROCK, VERY HARD, SLIGHTLY MOIST, RED, MAROON FORMATION RELATIVELY uNDlsruRBED DRtvE SAMPLE; 2-rNcH t.D. cALtFoRNIA LTNER sAMpLE. DRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH I.D. SPLIT sPooNSAMPLE, ASTM D-l586. 30/12 IFIYF -SA!,IPLE BLow coUNT. lNDlcATEs THAT 50 BLOWS oF A 140-PoUND HAMMERFALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES. I enlcrrcAL AUcER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JIJLY 27,2018 WITH A 4_INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BOR¡NGS WERE MEASURED APPROXIMATELY BY PACINGFROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. ÏHE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATEONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THEAPPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING OR WHEN CHECKED ON AUGUST 23, 2018, 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D ?216);DD = DRY DENSITY (PCt) (NSTU D 2216); -200= PERCENTAGE PASSING NO. 200 STEVE (ASTM D 1 1 40). 18-7 -451 H-PryKUMAR LIGEND AND NOTES Fig. 3 & É SAMPLE OF: Sondy Sill ond Ctoy FROM:Boringl@5' WC = 6.0 %, DD = l0S pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I I L {I I I fhtl.rkd, bt ¡ñ rilhoul ól ¡ I I I Ì I i JJ t¡J =vt I z.o F- ofo lr7z.oo 0 2 5 -4 -5 APPLIED PRESSURE - 18-7 -451 H-PryKUMAR SWELL-CONSOLIDATION TEST RESULTS Fis. 4 SAMPLE OF: Sondy Sitt ond Ctoy FROM:Boring2O5' WC = 6.9 ?6, gÐ = 92 pcl { 1 ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I I rl I l:I I il 2 N JLI =v, I z.o F ô Jolt7z.o(J 0 -t -4 -6 -8 -10 -12 t8-7 -451 H.PVKUMAR SWELL-CONSOLIDATION TEST RESULTS Fig. 5 H-P*lruMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. 18-7-451SOIL TYPESilty Clayey Sand withGravelSandy Silt and CIaySandy Silt and ClaySilty Sand with GravelSilty Sand with GravelUNCONFINEDCOMPRESSIVESTRENGTHATTERBERG LIMITSPLASTICINDEX(o/"1LIQUIDLIMIT(o/olNATURALDRYDENSITYGRAVELSANDPERCENTPASS¡NGNO.200SIEVE%t(%',36JJ25981039210'/106NATURALMOISTURECONTENT(o/ol6.56.06.95.94.2SAMPLE LOCATIONDEPTHtft)2%55I0I5BORING12