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Home My WebLink AboutSubsoil Studylcrtmåmfffiif';-- An Emdoycc otflrcd Compony 5020 CountyRoad 154 Gteûuruod Sptings Cll 81601 phone: (970) 945-7988 fax (970) 945-&454 emait kaglenwod@lumarusacom wtvr¡¡,kumâ¡rtsô.com Ofrc¿I¡c¿ttone: Dcq¡cr(IIQIP¡drer,ColondoSpings,FortColiüsrGlcnrôodSpeirgs,mdSrumitCotty,Coldado RECEIVED t',lAY 2 3 2rt22 GARFIELD COUNTY COMMUNITY DEVELOPMENT STJBSOIL STT]DY FOR FOT]NDATION DESIGN PROPOSED RESIDENCE LOT 114,IRONBRTDGE 295 SILVAR MOI]NTAIN DRTVE GARtr.IELD COTJNTY, COLORADO PROJECT NO.21-7-186 APRrL t+2021 PREPARED FOR: PATRICK \ilEST .ELDT 339 CLEYELA¡ID PLACE CARBONDALE, COLORADO 81623 Batrickbwestfeldt(Osmail.com TABLE OF CONTENTS PIJRPOSE AI.ID SCOPE OF STT'DY ........- 1 - PROPOSED CONSTRUCTION smE C0NDITIONS..... STJBSIDENCE POTENTIAL I I 2- 3 3- FIELD ÐGLORATION SIJBSTJRFACE CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS ....................... FOTJNDATION AND RETAINING WALLS ..........- 4 - FLOOR SLABS UNDERDRAIN SYSTEM.. STJF.FACE DRAINAGE LIMITATIONS................ FIGURE 1 - LOCATION OF ÐGLORATORY BORINGS AI.ID PTTS FIGURE 2 - LOGS OF Ð(PLORATORY BORINGS FIGTJRE 3 - SWELL.CONSOLIDATION TEST REST]LTS FIGURE 4 - GRADATION TEST RES{.JLTS TABLE 1- SUMMARY OF LABORATORY TEST RESIJLTS 5- 6- 6- Kumar t A¡soc{tb¡, lnc, o Prdcc{ No.2l-7-186 PTIRPOSE AIID SCOPE OF STTIDY This reportprese¡rts the results of a subsoil study for aproposed residence to be located on Lot 114, konbridge, 295 Silver Mountain Drive, Garfield County, Colo¡ado. The project site is shown on Figure 1. The purpose of the study was to deveþ recommend¿tions for the foundation design. The study was conducted in accordance with our agreement for geoteohnical engineering sen¡ices to Patick Westfeldt dated February 8,2021. The findings ofpreliminary subsurface conditions at the lot were presented in a report datod Mafch 4,2021. A freld elçloration program consisting of exploratory borings and hand dug pits was conducted to obt¿in information on the subsr¡rface conditions. Samples of the subsoils obtained during the field oxploration lvere tested in the laboratory to determine their classification, comltressibility or swell and other engineering cha¡acteristics. The results of the fíeld exploration and laboratory testing werc analyzed to dwelop recommendations for foundation types, depths and allowable pressures for the proposed þ¿ilrling foundation. This re,port st'mrnarizes the d¿ta obtained duing this study andpresents our conclusions, design recommendations and other geotechnical engine€ring considerations based on the proposed construction and the subsurface conditions encor¡ntered. PROPOSED CONSTRUCTION The proposed residence will be a two-story wood frame structr¡re with attached garage and possibly apafüalbasement level. Cround floors will be a combination of structr¡ral over crawlspace and slab-on-grade. Grading for the structure is assumed to be relatively minor with cut dçths between about 2 to 8 feet. We assume relatively light foundation loadings, t¡pical of the proposed tlpe of construction. Ifbuilding loadings, looation or grading plans change significantþ from those de.scribed above, we should be notifïed to re-evaluate the recommendations contained in this report. SITE CONII)ITTONS The subject site was vacant at the time of our field exploration. The ground surface is gently sloping down to the east at a grade of aror¡nd 5 percent in the area of the borings. The Roaring Fork River is east of and below the subject site. The ground surface east of the building a¡ea is sloping steeply down to the river as shown on Figure l. Vegetation consists of grass, weeds and sage brush. Kum¡r t Ascocld¡¡, lnc. o PloJoct No.2r-7-'186 -2- ST]BSIDENCE POTßNTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite r¡ndedies the honbridge Subdivision. These rocks a¡e a sequence of g¡psiferous shale, fine-grained sandsûone and silgtone with some massive beds of glpsum and limestone. There is a possibility that massive ryp$rm deposits associated with the Eagle Valley Evaporite rmderlie portions of the lot. Dissolution of the rypsum under certain conditions can car¡se sinkholes to deveþ and can produce areas of localized subsidence. During previous work in the alea, several si¡liholes were observed scattered throughout the honbridge Subdivision. These sinlùoles appear similar to others associated with the Eagle Valley Evaporiæ in areas of the lower Roaring Fork River valley. Sinl¡holes were not observed in the immediate area of the subject [ot. No evidence of cavities was encountered in the subsurface materials; however, the exploratory borings were relativeþ shallow, for for¡ndation desþ only. Based on or¡r present knowledge of the subswface conditions at the site, it cannot be said for certain that sinlùoles will not deveþ. The risk of future ground subsidence on Lot 114 throughout the service life of the proposed residence, in our opinion, is [ow; however, the owner shouldbe made aware of the potential for si¡lûole deveþment. If fi¡rther investigation of possible cavities in the bed¡ock below the site is desired, we should be contacted. FIELD EXPLORATION The field exploration for the project was conducted on Ma¡ch 3 and24,2021. Four pits were hand dug and three exploratory borings were drilled at the locations shown on Figure I to evalu¿te the subsu¡face conditions. The borings were advanced with 4 inch diameter continuous fligþt augers powered by a truck-mounted CME45B drill rig. The borinç were logged by a representative of Kumar & Associates, Inc. gamFles of the subsoils were taken ç'ith 1% inch and 2nchl.D. spoon samplers. The samplers were driven into the subsoils 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 penetation resistance values are an indication of the relative density or consistenuy of the subsoils. Depths at which the samples were taken and the penetation resistance values are shoum on the Logs of Exploratory Borings, Figure 2, T\e samples were returned to our laboratory for review by the project engineer and testrng. Kumar t À¡¡oclatso, lnc, o Proþct tlo.2f -7-186 -3- SI]BSURFACE CONDITIONS Graphic logs ofthe subsurface conditions encountered atthe site a¡e shown on Figure 2. T\e subsoils consist of about Yzfootoftopsoil overlying hard, sandy clay ûo between I and3Yzfeçt deep where dense, siþ sandy gravel with cobbles and probable bouldere was encountered down to the maximum explored dqth of 5% feet. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit. Laboratory testing performed on samples obt¿ined from the borings included natural moisture content and densþ and gradation analyses. Results of swell-consolid¿tion testing performed on a relativeþ undistr¡rbed drive sample of the clay soil, presented on Figwe 3, indicate low to moderate compressibility under conditions of loading and wetting. Results of a gradation analysis performed on a small diameter drive sample (minus lYz-nchfraction) of the coañ¡e granular subsoils are shown on Figrne 4. The laboratory testing is sr¡mmarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightlymoist. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and pits and the nature of the proposed constn¡ction, rrye rec(xnmend the building be founded with spread footings bearing on the natt¡ral granular soils. The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed on the undistrnbed natu¡al granular soils should be designd for an allowable bearing prcssure of 3,000 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about I inch or less. 2) The footings should have a minimum $'idth of 16 inches for continuous walls and 2 feet for isolated pads. 3) Exterior footings and footings beneath unheated areas should be provided with adeqr.rate soil cover above their bearing elevation for frost protection. Placement Kumar & A¡¡ocl¡taû, lnc. o Prcled tlo.2l-7-106 -4- 4) of found¿tions at least 36 inches below extErior grade is typicallyused inthis araa. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 10 feet. Foundation walls acting as retaining strucûues should also be designed to resist lateral earthpressures as discussed in the 'Fotmdation and Retaining Wallsu section of this report. Topsoil, upper cþ soils and any loose distr¡rbed soils should be re,moved and the footing bearing level extended down to the relativeþ dense natr¡ral granular soils. The exposed soils in footing area should the'n be moistened and compacted. A represe,ntative of the geotechnical engineer should observe all footing excavations prior ûo concrete placeme,lrt to evaluate bearing conditions. FOUNDATION AND RETAINING WALLS Formd¿tion walls and retaining shuctures which are lateralþ supported and can be expected to undergo only a slight amount of deflection should be desþed for a lateral earth pressure computed on the basis of an equivale,nt fluid unit weight of at least 50 pcf for backfill consisting of the on-site granular soils. Cantilevered retaining structures which are s€' aratÊ from the residence and can be expected to deflect sufficientþ to mobilize the full active earth pressure condition should be designed for a lateral earth pressure compuúed on the basis of an equivaleirt fluid unit weight of at least 40 pcf for backfill consisting of the on-site granular soils. All formdation and retaining stnrctr¡res should be designed for appropriate hydrostatic and surcharge pressr¡res such as adjacent footings, üaffic, consfuction materials and equipment. The pressr¡r€s recomm€nded 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 lateral pressure imposed on a foundation wall or retaining süucture. An underdrain shouldbe provided to prevent hydrostatic pressure buildup behind walls. Baclfill should be placed in uniforrr liffs and compacted to at least 90% of the manimum standard Proctor densrty at a moisture content near optimum. Bacldill placed in pavement and wallcrnray areas should be compacted to at least 95o/o of the mærimum standard Proctor densþ. Care should be taken not to overcompact the backfill or use large equipment near the walln since this could caute excessive lateral prcssrre onthe wall. Some settle,ment of dee,p for¡ndation wall backfill should be expected, even if the material is placed correctþ, and could result in disfress to facilities constucted on the backfill. 5) 6) Kumer & Argoclabs, lnc. c Prolcct llo.2t.7.l80 5 The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footrng 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 calcul¿ted based on a coefficient of friction of 0.45. Passive pr€ssr¡r€ of compacted backfill against the sidss of the footings can be calculated using an equivale,nt fluid unit wçight of 400 pcf. The coefficient of friction and passive pressrre values recomme,lrded above ar¡sume ultimate soil süength. Suiøble factors of safety should be included in the design to limit the sEain which will occur at the ultimate stength, particularly in the case ofpassive resistance. Fill placed against the sides of the footings to resist lateral loads should be a granular material compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. Fill can consist of the onsite soils devoid of topsoil and oversized (plus 6-inch) rock. FLCIOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support ligbtly loaded slab-on-grade construction. To reduce the effects of some differe,ntial mov€,ment, floor slabs should be separated from altbearing walls and columns with expansion joints which allow r¡nrestained vertical movement. Floor slab confiol joints should be used to reduce damage due to shrinkage cracking. The requireme,nß forjoint spacing and slab reinforceme,nt should be established by the designer based on experie,nce and the intended slab use. A minimum 4 inch layer of free- draining gravel should be placed beneath basement level slabs to facilitaæ drainage. This m¿terial should consist of minus 2 luorch aggregate with at lø,st 50o/o ret¿ined on the No. 4 sieve and less lhan z%passing the No. 200 sieve. Alt fill materials for support of floor slabs should be compacted to at least 95% of ma¡rimum standard Prootor density at a moistr¡re content near optimum. Required fill can consist of the on' site granular soils devoid of vegetation, topsoil and oversized rock. I'NDERDRAIN SYSTEM Atthough free w¿ter was not e,ncountered during our exploration, it has been otn experience in the a¡ea that local perched groundwater can dwelop dwing times of heavy precipitation or seasonal runofn Frozen ground during spring runoffcan create a perched condition. We recommend below-grade constructior¡ such as retaining walls, crawlqpace and basement areas¡, be protected fiom wetting and hydrostatic pressure buildup by an underdrain syst€m. The d¡ains should consist of drainpipe placed in the bottom of the wall backfill surror¡nded above the invert level with free-draining granular material. The drain should be placed at each level of Kumer&A¡¡oclabq lnc.c PruþdHo.2l.7-186 -6- excavation and at least I foot below lowest adjacent finish grade and sþed at a minimum 1%to a suit¿ble gravity outleÇ sump and pump or drywell. Free-draining granular material used in the underdrain system should contain less than 2Vopassngthe No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least l% feet deep. SURFACE DRAINAGE The following drainage precautions should be observed during constnætion and maintained at all times after the reside,nce has becn completed: l) Inundationofthe for¡ndationexcavations andunderslab a¡eas shouldbe avoidd ùring construction. 2) Exterior backfill should be adjusúed to near optimum moisture and compacted ûo at least 95Yo of the maxinum standard Proctor density in paveinent and slab areas and to at least 90% of the ma¡rimum standard Proctor density in landscape areas. 3) The ground surface surounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend ¿ minimum slope of 12 inches in the first l0 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. Free{raining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site finer graded soils to reduce surface water infiltation. 4) Roof downspouts and drains should discharge well beyond the limits of all baclfill. 5) Landscaping which requires regular heavy irrigation should be located at least 5 feet from foundation walls. LIMITATIONS This study h¿s been conducted in accordance with generally accepted geotechnical engineering principles and practices in this are,a atthis 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 oçloratory borings drilld and pits excavaûed at the locations indicated on Figure 1, the proposed t1rye of construction and our experience in the area. Our services do not include determining the prese,nce, preve,ntion orpossibility of mold or otherbiological contaurinants (MOBC) deveþing in the future. If the client is concemed about MOBC, then a professional in this special field ofpractice should be consulted" Our findings include interpolation and Kumar&As¡ochbo, lnac Proþd llo.2l.7.l80 -7 - extrapolation of the subsurface conditions identified at the exploratory borings and pits and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear diffbrent 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 veriff 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 ofstructural fill by a representative of the geotechnical engineer. Respectfully Submitted, Kumar dl¿ Associates, Inc' grrrrurÈ.PM { JamesH. Parsons, P.E. Reviewed by: Steven L. JHP/kac t tt l* tl,52212I Kunrar & rXss+cial*s, lnc"Prr,rj*ct Fl*. ;1-T"l 8{i I "r'^ tìtt. (__,,,.... "...''_r.'\.\\\\ BORlltG I \\ O 5 FEEI 10 GRAVETI 2.5 ÍEET GNAYEL / t \ \r[*,'çli"--*;,'.-]BORING BORING 5 J (î I 2.23 GRAyET ti T FEN 10 GRAYELr !!!ÌtBt:.qfgu_ltÍt-! L 'e,z tt+ l;iìi:f"" \ LOT'tfs d LEGEND: o BoRTNG LOCATTON I HAND DUG PIT LOCATION 1 APPROXIMATE SCALE-FEET Fig.1LOCATION OF EXPLORATORY BORINGS AND PITS21-7-186 Kumar & Associates d BORING 1 EL. 5992.5' BORING 2 EL. ã990.5' BORING 5 EL. 5992.5' t-r¡Jl¡lL I :EFLl¡¡c¡ 00 55 e/6, 31/6 WC=S.1 DD=1 1 I 5o/3 50/s 50/5 21/6, 50/6 so/1 l-ùl l¡Jl! I T FL l¡Jo LEGEND n W F I TOPSOIL: C¡-AY, SANDY, ORGANICS, FIRM, SLIGHTLY, MOIST, BROWN. CI-AY (CL); SANDY, I{ARD, MOIST TO SLIGHTLY MO¡ST, TAN AND GREY. sANDy, SILW, COBBLES, POSSIBLE BOULDERS, DENSE, SLIG|{TLY MOIST, GREY ROUNDED ROCK. cRAvEL (cM); AND BROWN. DRIVE SAMPLE, 2.1NCH I.D. CATIFORNIA LINER SAMPLE. DRTVE SAMPLE, I s/8-tNcl{ l.D. SPLIT SPOON STANDARD PENETRATION TEST. ,^r.- DRIVE SAMPLE ELOW COUNT. INDICATES THAT 40 BLOWS OF A I¡+O-POUND HAMMER+v/ tz FALLTNG 50 rNcHEs wERE REQUIRED To DRtvE Tt{E SAMpLER 12 tNcHEs. I nnlcrrclL AuGER REFUsAL. NOTES I. THE EXPLORATORY BORINGS WERE DRILLED ON MARCI{ 21, 2021 WlÏH A 4-INCI{ DIAMETER CONTINUOUS-FLIGHT POWER AUGER. THE PITS WERE HAND DUG ON T4ARCH S, 2021, Z. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROX]MATELY BY TAPING FROM FEATURES SHOWN ON THE SITE PI.AN PROVIDED. 5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOI.ATION BETWEEN CONTOURS ON THE SITE PI-AN PROVIDED. 1. 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 THE EXPLORATORY BORING LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETIYEEN HATERIAL TYPES AND THE TRANSITIONS ITAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILL¡NG. 7, I¡BORATORY TEST RESULTS¡wc = WATER CONTENI (f) (ASTM o2216); DD = DRY DENSTTY (pct) (aSrU D2216);+1 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM 06915); -200= PERCENTAGE PASSING NO. 200 S¡EVE (ASTM Dll4O). WC=2.4 +4=52 -200= I 3 LOGS OF EXPLORATORY BORINGS Fig. 221-7-186 Kumar & Associates d SAMPLE OF: Sondy Cloy FROM: Borlng f O l' WC = 5.1 X, DD = 111 pof¡ i Ì ì I il --i -. il NO MOVEMENT UPON WETTING !il itrii.ri tlr,liii I-l 1 I I I I ¡ I ii I I I I ì I I ì I I i I-l I I I I.! I I t ilir 'ilr i I a I ii l, It. I l i iiiir,i'lrtiliirit'ìtii::ii I l t I i I 1 I I I I I I i ..i.. I ¡ I I-¡ ii ii iì il,rl:iìillriì iiiiiiììilir I 1iitlii!iitiìi I 1 I I I I J ! I'I I I I I Ì ]l1i ii ! I I I I 1 I I iiÌlr rit!irii iliril:rlil,,tliri ,i,riirlillti1ìli:li L - I r ' ,- iilïli lltilriliìt li1r Iii I I I I J I I I l ! I Il iiiiilii l t I I ! I I I ì I I ì I ¡ l tj i I i I I iI I : i ¡l I ì I I ili¡IIri ! I I ¡ I Ì iiilil ri f 0 à( l-1l¡¡ =an t_2 zo $-soû-o<s -1 SWELL-CONSOLIDATION TEST RESULTS Fí9. 521-7-186 Kumar & Assoclates ! ¡ lo zß ¡þ ,o lo to to lo a0 Ë E DIATETER OF CI¡Y TO SILT COBBLES CRAVEL â2 X UQUID UYTÍ sND 55 X PIISÏICITY INDEX stlï AND Ct¡Y t5 X S lrPt"E OF: Sllty Sondy GrcYcl FROH¡ Borlng 2 C 1' e l" (Gomblncd) thð td lnllr o¡Dlt dlt to thrlffiplq rhloh r.r ltrH. lü.Hlne nporl dìoll rþt b. nÞÉdu€d..rupt ln lull. rËhod tf. rrillmoÞÞml of Kumr t l'odclr., lEs.Yr orcl'lb tr.il!! h p.rlomd frsordom rllfi AglÍ 06e15, Alrî¡ D7rrl, Aslta ClSt andlü ASil oltao, SIEVE AIIALYSISHYDNOTEÍEN ANALITIS ¡4 tn ffiffi tùr I I I I / I I '¡ I I ¡! I I I I i I I I I .l I I ! SAND GRAVEL MEDIUX FINE COARSEFINE Fig. 421-7-186 Kumar & Associates GRADATION TEST RESULTS l(+rtf,tme&Assochbq lno.@Geotechnical and Materials Engineersand Envimnmental ScientisbTABLE ISUiITARY OF I.ABORATORY TEST RESULTSNo.2l-7.1862IBORIilG1&4combinedItñtDEPfI{2.45.1pÁtilAruRALIOßTUREooilTEt{Î111ilAruRALDRYDEI{sITYlûcñ52(el)GRAYET(t|,8r¡{DGRADAfloil3513PERCEf,fPASSilGT{O.2008tEtEuQuDufffftÊtPLASNCItftExfÍìfDûñulrooi¡FNEIDCOflPRESSIYESifRETgIHSandy ClaySOIITY?ESilty Sandy Gravel