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HomeMy WebLinkAboutSubsoil Study for Foundation Design 01.26.17H-PvKUIVIAR 5020 Gounty Road 154 Glenwood Springs, CO 81601 Phone: (970) 945.7988 Fax (970) 945'8454 Emall: hpkglenwood@kumarusa.com Geotechnical Engineeríng I Engineeríng Geology l,laterials Testing I Envlronmental Office Locations: Parker, Glenwood Springs, and Silverthome, Colorado f{EctfT'tË} DEc 07 ?0n ,fi #[ñ',i,'f,,fff Hf;i,,y*,SUBSOIL STUDY FOR F'OUNDATTON DESIGN PROPOSED RESIDDNCE AND SHOP 899 GAGE ROAD GARFIELD COUNTY, COLORADO I,ROJECT NO. t7-7-il1 JANUARY 26,20t7 PREPARED FOR: HEATH COTTER 752 CACTUS COURT, RIFLE, COLORADO 81650 (heath cottcr@gmal.com) T,ABLE OT CONTENTS PUR.POSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS....... FIELD EXPLORATION. SUBSURFACE CONDITIONS DES IGN RECOMMENDATIONS FOLINDATIONS FOIJNDATION AND RETAINING TYALLS FLOOR SLABS UNDERDRATN SYSTEM.. SURFACE DRAINAGE...,.. LIMITATIONS FIGURE I - LOCATION OF EXPLORAI'ORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FICURE 3 - LEGEND AND NOI'ES FIGURES 4 AND 5 - SVI/ELI.-CONSOLIDATION TEST RESULI'S TABLE I - SUMMARY OF LABORATORY TEST RESULTS -t - -t - ,........- 2 - _) - 7- H.P s KUMAR Project No, 17'7-1 1 1 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence and shop building to be located at 899 Gage Road, south of the Rifle Airport, Garfìeld County, Colorado. The project site is shorvn on Figure 1. The purpose of the study rvas to develop recommendations for the foundation design. The study rvas conducted in accordance rvith our agreement for geotechnical engineering sen'ices to you dated January 9,2017. A fìeld exploration progrâm consisting of exploratory borings rvas conducted to obtain information on the subsurface conditions. Samples of the subsoils and bedrock obtained during the field exploration rvere tested in the laboratory to determine their classification, compressibility or srvell and other engineering characteristics. The results of the lield exploration and lal¡oratory testing s'ere analyzed to develop recommendations for foundation t1'pes, depths and allorvable pressures for the proposed building foundation. This report summarizes tlte data obtained during this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed co¡rstruction and the subsurface conditions encountered PRO POSE D CONSTIIUCTION The proposed residence rvill be a one story concrete structure abot'e a full basement. "fhe shop building rvill be one story u'ood frame construction. Ground floors rvill be slab-on-grade. Crading for the slructures is assumed to be relatively minor rvith cut depths betrveen about 3 to 9 feet. l/e assumc relatively light foundafion loadings, typical of the proposed type of constructìon. If building loadings, location or grading plans change significantly from those described above, rve should be notified to re-evaluate the recommendations contained in this report, SITE CONDITIONS The building site is located noñh and rvest of Gage Road and accessed by an existing trvo track H-P t KUMAR Project No 17.7-111 .\ drivervay. A partially buried rvater tank is located on the site. 1'lre area is vegetatecl rvith scatteredjuniper trees, sage brush, grass and rveeds. There rvas about 4 inches ofsnorv cover at the time of our exploration. The ground surface slopes strongly down to the rvest. Small boulders and cobbles are visible on the ground surface. FIELD EXPLORATION Tlre field exploration for the project rvas conducted on January 16,2A17. Two exploratory borings were drilled at the locations shorvn on lrigure I to evaluate the subsurface conditions. The borings were advanced rvith 4 inch dianreter continuous flight augers powered by a truck- mounted CME-458 drill rig. The borings rvere logged by a represcntative of I'l-P/Kumar. Sanrples of the subsoils *ere takert rvith a 2 inch l.D. spoon sampler. The sampler rvas driven into the subsoils at t arious depths rvith blorvs from a 140 pound hammer falling 30 inches. This test is similar to the sfandard penetration test described by ASTM Methocl D-I586. The penetration resistance values are an indication of the relative density or consiste¡rc¡'of the subsoils and hardness of the bedrock. Depths at rvhich the samples rvere taken and the penetration resistance values are shorvn on the Logs of Exploratory Borings, Figure 2, The sanrples rvere returned to our laboratory for revierv by the projecl engineer and testing. SUBSURFACE CONDITIONS Graphic logs of the subsurlace conditions encountered at the site are shorvn on Figure 2. The subsoils belorv about 6 inches of topsoil consist of l%to 3Vz feet of sandy silty clay overlying claystonclsandstone bedrock. Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of srvell-consolidation testing perlormed on relatively undisturbed drive samples of the claystone portion of the bedrock, presented on Figures 4 and 5, indicate lorv compressibility under existing moisture conditions and light loading and a lorv lo nroderate expansion potential when rvetted. The laboratory tcsting is summarized in Table l. H.P * KUMAR Project No 17-7-111 --7- No free rvater lr'as encountered in the horings at the time of drilling and the subsoils and bedrock rvere slightly moist to moist. DESIGN RECOMMENDATIONS FOTINDATIONS Considering the subsurface conditions encounlered in the exploratory borings arrd the nature of tlie proposed construction, we recommend the building be founded rvith spread lootings bearing on the claystonelsandstone bedrock, 'l'he design and construction criteria presented belorv should be observed for a spread footing foundation system. l) Footings placed on the undisturbed claystone/sandslone should be designed lor an allorvable bearing pressure of 4,000 psf. To help mitigate the expansion potential of the claystone bedrock, 1ve recommcnd that the footings also be designed for a minimum dead load pressure of 1,000 psf. Based on experience, we expect settlenrent/heave of footings designed and constructed as discussed in this section will be about I inch or less. 2) The footings should have a minimum rvidth of l6 inclrcs for continuous rvalls and 2 feet for isolated pads. 3) Exterior footings and footings beneath unheated areas shor.rld be provided tvith 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 rvalls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least l4 feet. Foundation rvalls acting as relaining structures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) All topsoil, sandy silty clay and any loose or disturbed soils should be removed and the footing bearing level extended dorvn to the relatively fìrm bedrock. If H.P \ KUMAR Project No. 17-7-1 1 1 4 rT'ater seepage is encountered, the footing areas should be dervatered belore concrete placement. A representative of the geoteclrnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION AND RETAINTNG WALLS Foundation rvalls and retaining structures rvhich are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit rveight of at least 55 pcf for backfill consisting of the on-site soils and rvell-broken bedrock fragments. Cantilevered retaining structures rvhich are sepârate fronl the resídence and can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral eadh pressure computed on the basis of an equivalent fluid unit rveight of at least 45 pcf for backfìll consisting of the on-site broken bedrock liagmen(s. All founclation and retaining struclures should be dcsigned for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures recommendecl above assume draincd conditions behind the rvalls and a horizontal backfìll surface. The buildup of rvater behind a rvall or an upward sloping backfill surface rvill increase the lateral pressure imposed on a foundation rvall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind rvalls. Backfill should be placed in uniform lifts and compacted to at least 90% of thc maximum standard Proctor density at a moisture content slightly above optimum. Backfill in pavement and *'alkrvay areas should be compacted to at least 95% of the maximum standarcl Proctor density. Care slrould be taken nût to overcompact the backfill or use large equipment near the rvall, since this could cause excessive lateralpressure on the rvall. Some settlement of deep loundation rvall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. 6) H-P \ KUMAR Project No, 17-7-1 I 1 -5- We recommend imported free-draining granular soils for backfìlling fbundation rvalls and retaining structures because their use resulls in lorver lateral earth pressures and the backfill can be incorporated into the underdrain system. Subsurface drainage reconrmendations are discussed in more detail in the "Underdrain System" seclion of this report. Imported [free-draining] granular r.vall backfìll should contain less than [5% 15%) passing the No. 200 sieve and have a maximum size of 6 inches. The lateral resistance of foundation or retaining rvall footings rvill be a combination of the sliding resistance of the footing on the foundation mater¡als and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings placed on the bedrock can be calculated based on a coefficient of friction of 0.50. Passive pressure of compacted backfillagainst the sides of the footings can be calculated using an equivalent fluid unit rveíght of 375 pcf. The coefficient of friction and passive pressure values recomnrended above assume ultinrate soil strength. Suitable factors of safety should be included in the design to limit the strain w'hich 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 95% of the maximum standard Proctor density ât a moistufe content near optimum. FLOOR SLABS The natural on-site clay soils and bedrock, exclusive of topsoil, are suitable to support lightty loaded slab-on-grade construction. To reduce the effects of some differential movement, floor slabs should be separated front all bearing rvalls and columns rvith expansion joints rvhich allorv unrestrained vertical movement. Floor slab controljoints should be used to reduce damage due to shrinkage cracking. The requirements forjoint 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 co¡rsist of minus 2 inch aggregale rvith at least 50% retained on the No.4 sieve and less than 2% passing the No. 200 sieve, H.P x KUMAR Project No. 17-7-11'l -6- All fìll materials for support of floor slabs should be conrpacted to at least 95% of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site granular soils devoid of vegetation,lopsoil and oversized rock. UNDERDRATN SYSTEM Although free n'ater was not encountered durirtg our exploration, it has been our experience in areas rvhere bedrock is shallow that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also creale a perched condition. We reconrmend belor,v-grade construction, such as retaining rvalls, crarvlspace and basement areas, be protected f'rom rvetting and hydrostatic pressure buildup by an underdrain system. The shop rvill be a slab-at-grade structure rvhich should not require an underdrain. Where inslalled, the drains should consist of drainpipe placed in the bottom of the rvall backlill surrounded above the invert level rvith free-draining granular material. The drains should be placed at each level of excavation and at least 1 foot belorv lorvest adacent hnish grade and sloped at a nrinimum lYa to a suitable gravity oullet. Frec-draining granular malerial used in the underdrain systcm should contai¡r less than 2% passing the No. 200 sieve, less than 50?'o passing the No. 4 sieve and have a maximum size of 2 inches. 'l'he drain gravel backfìll should be at least I Vz feú deep. An inrpervious nrembrane such as 20 mil PVC should be placed bcneath the drain gravel in a trough shape and attached to thc foundation rvall rvith mastic to prevent rvetting of the bcaring materials. SURITACE DRAINAGE The lollorving drainage precautions should be observed during construction and maintained at all times after the residence and shop building lrave been completed: l) I¡rundation of the foundation excat,ations and underslab areas should be avoided during construction. H.P s KUMAR Project No. 17-7-111 -7 - 2)Exterior backfill slrould be adjusted to near optimum nroisture and compacted to at least 95o/o of the maximum slandard Proctor density in pavement and slab areas and to at least 90o/o of üte maximunr standard Proctor density in landscape areas. The ground surface surrounding the exterior of the building should be sloped to drain arvay from the foundation in all directions. We recornmend a minimum slope of l2 inches in the first l0 feet in unpaved areas and a minimum slope of 3 inches in the first l0 feet in paved areas. Free-draining rvall backfill should be capped rvith about 2 feet of the on-site soils to reduce surface rvater infìltration. Roof dorvnspouts and drains should discharge rvell beyond the limits of all backfill. Landscaping rvhich requires regular heavy irrigation should be located at least l0 feet from foundation rvalls. Consideration should be given to use of xeriscape to reduce the potential for rvetting of'soils belorv the building caused by irrigation. 3) 4) 5) LIMITATIONS This study has been conducted in accordance rvith generally accepted geotechnical engineering principles and practices in this area at this time. We nrake no rvarranty either express or implied. The conclusions and reco¡nmendations submitted in this report are based upon the data obtained from the exploratory borings drilled at the locations indicated on Figure l, the proposed typc of construction and our experience in the area. Our services do not include deternrining 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 perbrmed. lf conditions encountered during construction appear different from those described in this report, rve should be notifìed so that re-evaluation of the rccommendations may be made, This report has been prepared lor 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, rve H-P K KUMAR Project No 17'7-111 -8- should provide continued consultalion and fìeld sen'ices during construclion to revierv ancl monitor the implementation ol'our recommendations, and to verify that the recomnrendations have been appropriately interpreted. SignifÏcant design changes n:ay require additional analysis or modifications 1o the recommendations presented herein. Vy'e recommend on-site observation of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfirlly Submitted, H-P* KU ts E. Eller Revieu'ed by Daniel E. Flardin, P.E. LEE/kac H.P \ KUMAR Project No. 17-7.1 1 I s ¡ È 6 PROPOSED SHOP BU|LDTNG o BOFING 2 19 ÊXISTING WATEFI TAf'lK PBOPOSEO RESIDÉNCE BORING 1 o BÊNCHMARK: TOP OF WATEH TANK; EL*1ffi', ASSUI,/ED ÊOAD APPROXfMA'IE SCALE_FEET VICINIÍY MAP SCALE: 1"=600' Ë 8r,{ 0t tô s¡l¡I I -t soÈ I I 17 *7 *111 H-PryKUMAR LOCATION OF TXPLORATORY BORINCS Fíg 1 f ; ¡ ¡ BORIHG 1 EL. 103' RESIOENCE EORING 2 EL. 86' SHOP 0 0 st /12 WC=5.6 DD=75 56/t2 WC=6.7 DD=1 25 5 %/6,5a/1 567/t2 t0 5ø/3 27 /6.30/ 4 WC=6.2 DD= I 28 t0 l-t¡l t¡JLr IIt-fL l¡Jcl l'-t¡J t¡Jl¡- t5 34/6,5t/ t $/C= l0.l 0Ð= 1 26 t530/ t zo ss/2 2A 25 ?5 17-7-111 H-PryKUMAR LOGS OF IXPLORATORY BORINGS Fig. 2 I É I r E LEGEND ñ ï0PSO|L; ORGANIC SANDY SILT AND CLAY WITH GRAVEL, F!RM, MO|SI, DARK BROWN. CLAY (cL); SANDY, SILTY, VERY STIFF, SLTGHTLY MOtsT, LTGHT BROWN ñl kil CLAYSTONE/SANDSTONE BEDROCK; HARD, SLIGHTLY MOIST TO MOIST, MIXED LIGHT BROWN AND GRAY. F RELATIVELY UNDISTURBEO DRIVE SAMPLE; 2-INCH l.D. cALIFoRNtA LTNER SAMPLE ai/1? DRIVE SAMPLE BLOW COUNT. lNOlCATEs THAT 3l BLOWS OF A 140-POUND HAMMER-.,'- FALLING 50 INCHES WERE REQU¡RED TO ORIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES. NOTES 1 THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 16,2017 WITH A 4-]NCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2, THE LOCATIONS OF THE EXPLORATORY BORINGS WËRE MEASURED APPROXIMATELY BY PACING FROM FEATURTS SHOWN ON THE SITE PLAN PROVIDED. 3, THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HANÐ LEVEL AND REFER TO THE BENCHMARK ON FIG. 1, 4. THE EXPLORATORY EORINO LOCATIONS AND ETEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USEO. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORINC LOGS REPRE5ENT THE APPROXIMATE BOUNDARIES 8ITWEEN MATERIAL TYPES AND THE TRANSITIONS MAY 8E GRAOUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE EORINGS AT THE TIME OF DRILIING. 7. I.ABORATORY TEST RESULTS: WC = IYATER CONTENT (Z) (ASTM O 2216)Z DD = DRY DENSITY (pcf) (ASTM D 2216). 17-7-111 H-PryKUIVIAR LEGEND AND NOTTS Fig. 3 t e d I I SAMPLE 0F: Cloyslona/Scndslone Bedrock FROMrBorlng 1O 15' WC = 10. I %, ùD = 126 pcf EXPANSION UNDER CONSTANÍ PRES5URE UPON WFNING 4 5 x J l¡l3t/, I o (¡ J C'vlzo(J z 1 0 -t -z t00 ñ l¡.13v, I zoË f3 Io,/tzo(J 2 I 0 -1 -2 SAMPLE OF: Cloyslone/Sondslone Bedrock FROM:Borlng 2O2.5' \{C = 6.7 %, OD = 123 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 17 -7-111 H-PVKUTVIAR SWELL_CONSOLIDATION TTST RESULTs Fig. 4 SAMPLE OF: Cloyslone/Sondslone Bsdrock FROM:Borlng 2ø 10' YIC = 6.2 %, DÐ = 128 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 0 j-1 t¡, =tn t-2 z.I c¡ oU'z.o(,_4 17 -7 * 111 H-PTKUIVIAR SWELL-CONSOLIDATION TTST RESULT Fis. 5 H-PvKUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProjectNo. 17-7-111SOIL OR BEDROCKTYPESandy Silty ClayClaystone/SandstoneClaystone/SandstoneClaystone/SandstoncSWELLtslLl3.91.91.4SWELLPRESSURE{PSFT7,0004,0002,800AÎÎËRBERG LIfIIITSPt-ASTtCINDEXP/.1LIQUIDLIMfTa%lPERCENÎPASSINGNO.200SIEVENATURALIIOISTURECONTENTNATURALDRYDENSITYGRAVELSANDtmt%t75t261231285.610.16.76.2-oCATIONBORINGoEPll{2Y2l5?r/"l0SAMPLEI2