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Home My WebLink AboutSubsoil Study for Foundation Design 07.03.2017H.PryKUMAR 5020 County Road 154 Glenwood Springs, C0 81601 Phone: {970) 945-7988 Fax (970) 945'8454 Email: hpkglanwood@kumarusa.com Geotechnlcal Englneering I Englneedng Geology Matarlals Testing I Envlronmental 0flice Localions: Pa¡kar, Glenwood Springs, and Silverthorne, Colorado SUBSOIL STUDY FOR FOUNDATTON DESIGN PROPOSED RDSIDENCE LOT 65, FILING 2, PTNYON MESA TBD PAINTBRUSH \ryAY GARnELD COUNTY, COLORADO PROJECT NO. t7-7-391 JULY 3,2A17 PREPARED FOR: INTEGRATtrD MOUNTAIN DEVBLOPMBNT, INC. ATTN: JIM GORNICK P.O. BOX 908 cLEN\ryOOD SPRINGS, COLORADO 8t602 tjeorntsk9spp¡is.ns!) TABLE OF CONTBNTS PURPOSE AND SCOPE OF S"UDY PRCIPOSED CONSTRUCTION SITE CONDITIONS SUBSIDENCE POTENTIAL................ FIELD EXPLORATION SUBSURFACE CONDTTIONS FOUNDATION BEARTNC CONDITIONS DESTCN RECOMMENDATIONS ....................... FOUNDATIONS FOUNDATION AND RETAININC WALLS FLOOR SLABS.,.... UNDERDRAIN SYSTEM ........ -t _ I 2- 2- _?_ ..-3- ..-4- -\_ 4- 5- 6- 8-SURFACE DRATNAGE ............... LIMITATTONS FICURE I . LOCATION OF EXPLORATORY BORINC FIGURË 2 . LOG OF EXPLORATORY BORING FICURE 3 - SWELL-CONSOLIDATION TEST RESULTS TABLE I- SUMMARY OF LABORATORY TEST RESULTS 8- H-PIKUIVIAR Project No. '17-7-391 PURPOSE AND SCOPB OF STUDY This report presents the results of a subsoil sludy lor a proposed residence to be located at Lot 65, Filing 2, Pinyon Mesa, TBD Paintbrush Way, Garfield County, Colorado. The project site is shown on Figure l. 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 Integr¿¡ted Mountain Development, Ins. dated May I1,2017 . An cxploratory boring was drilled to obtain information Õn the subsurface conditions. Samples of the .subsoils and bedrock obtained during the lÌeld exploration were tesfed in thc laboratory ro determine their classification, compressibility or swell and other engineering char¿cteristics. The results of thc field exploration and laboratory testing rvere analyzed to develop recommendations for foundation types, deplhs and allorvable pressures for tlrc proposed building foundation. This reporl. sumnrarizes the data obtained during this.study and presents our conclusions, design ¡ecommendations and other geotechnical engineering considerations based on the proposed conslruction and the subsurface conditions encountcred. PROPOSßD CONSTRUCTION The proposed residence will be a two-story structurc above a basement ¿nd with an attached gärí¡ge. Basement and garage floors will be slab-on-grade. Grading for the structure is assumecl to be relatively minor with cut depths between about 3 to l0 fcet. 'We assume relatively lighr foundatio¡ loadings, typicalof the proposed type of construction. If building loadings, location or grading plans change significantly liom those described above, we should be notified to re-evaluate the recommendations contained in this report. SITB CONDITIONS The property is vacant and vegetated with sage brush, grass and weeds. Vegetation in the f ront parl of the site has been removed during the subdivi.sion development. The ground surface is H.P+KUMAR Project No. 17-7-391 -2- relatively flat in the building envelope with a slight slope down to the southwest. A deep gully is located beyond lhe rear building envelope line. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the Pinyon Mesa Development. These rocks are ¿l sequence of gypsiferous shale, fìne-grained sandstonelsiltstone and limestone with some massive beds of gypsum. There is a po.ssibility that massive gypsum deposits associated with tlæ Eagle Valley Evaoprite underlie portions of the property. Dissolution of the gypsum under certain conditions can cÂuse sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, sinkholes have been observed scattered throughout the lower Roaring Fork River valley. No evidence of subsidence or sinkholes were observed on the property or encountered in the subsurface materials, however, the exploratory borings were relatively shallow, for foundation design only. Based on our pre.sent knorvledge of the subsurface conditions at the site, it cannot be said for certain that sinkhales will not develop. The risk of future ground subsidence at the site throughout the service life of lhe structure, in our opinion is low, however the ow¡ler should be aware of the potential for .sinkhole dcvelopment, If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. FIELD I'XPLORATION The ñeld exploration for the project rvas conducted on May 16, 7Al7 . Ane exploratory boring was drilled at the location shown on Figure I to evaluate the subsurface conditions. The boring was ndvanced with 4-inch dianleter continuous fiight augers powered by a truck-rnounted CME- 458 drill rig. The boring rvas logged by a repre.sentative of H-PlKumar. Samples of the suh.soils were taken with a 2 inch [.D. spoon sampler. The sampler was 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 H-PIKUMAR Projecl No. 17-7"391 -3- penetration rcsisfance 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 Log of Exploratory Boring, Figure 2. The samples were relurned lo our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The subsoils, below about I foot of fill, consist of very stiff sandy clay to l2 feet and sandy silt and clay to 23 feet overlying medium hard to hard siltstone bedrock down to 3l feet. Laboratory testing performcd on samples obtained from the boring included natural nroisture content and density and percent finer than sand size gradation analyses. Results of swell- consolidation testing performed on relatively undisturbed drive samples of the clay and silt soils, presentcd on Figure 3, indicatc low to moderate compressibility under conditions o[ loading and wetting with a low collapse potential (settlement under constant load) when wetted. The Iaboratory testing is summarized in Table l. No free wate r was encountered in the boring at the time of drilling or when checked on June 15, 2017 and tlre subsoils and bedrock were slightly moist. TOUNDATION BtrARING CONDITIONS The sandy clay and silt soils encountered af lypical shallow foundation depth mainly tend to settle when fhey become wetted. A shallow foundation plnced on these soils will have a risk of setllement if the soils become wetted and care slrould be taken in the surface and sub.surface drainage around the house to prevent the bearing soils from becoming wet. It will be critical to the long-term performance of the structurc that the recommendations for surface grading and subsurface drainage contained in this report be followed. The ãmount of settlement, if the bearing soils become wel, will mainly be related to the depth and extent. of .subsurface wetting. We expect that initial settlements will be le.ss than I inch. If wetting of the shallow soil.s occurs, H-PÞKUMAR Proiecl No. 17-7-391 4 additional setllerltents of I to I /r inches could occur and cause building distress. Mitigation methods such as a deep lìoundation (piles or piers extending down about 25 to 30 feet below existing ground surface and into bedrock) or removing and replacing lhe bearing soils with compacted structural fill should be used to support the proposed house with a lower risk of settlement. If a deep foundation is desired, we should be contacted to provide further design recommendations. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions sncountered in the exploratory boring and the naturc of the proposed construction, tlle building can be founded r.vitlr spread footings bearing on compacted structural fill. The design and construction criteria presented below should be <¡b.çerved for a sprcud looting foundation systenr. I ) Footings placed on compacted .structural fill shculd be designed for an allowable bcaring pÍcssure of 1,200 psf. The basement and garage footing areas should be .sub-excavated down about 6 to l0 feet below exisling ground surface and the excnvated soil replaced with compacted struclural fill back to design grade. The sub-excavated areas should extend clown at least 3 feet below the footing bearing level. Based on experience, we expect initial settlcmenf of footings designed and constructed ¿s discusred in this section rvill be about I inclr or less. Additional settlements o[ about ¡/z to I inch could occur if the bearing soils are wetted. A '¡i increase in the allowable bearing pressure can be t¿ken for toe pressure of eccentrically loaded (retaining wall) footings. 2) The footings should have a minimum width of 20 inches for continuous walls and 2 {eet for i.solated pads. 3) Ëxlcrior footings and footings beneath unheated areas should be provided with adequate soil cover above their be:rring elevalion for frost protecf ion. Placement H-P4KUMAR Projecl No, 17.7-391 5 4) of loundations ût least 36 inches below exterior grade is typically used in this area. Continilous foundation walls should be heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported lcngth of at least l4 feet. The foundation should be configured in a box like shape to help resist differential movements. Foundaiion walls acting as retaining structures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Vy'alls" section of this report. The topsoil, sub-excavation depth and any loose or disturbed soils should be removed below the foundation area. The exposed.çoils in footing areas after sub- excavation should then be nloistened and compacted. Structural lill should consi.st of lorv permeable soil (such as the on-site sandy clay and silt soils) compacted to at ¡eâst 98Vo ol standard Proctor density within 27o of optimum moisture content. The structural lill should extend laterally bcyond the footing edges equal lo at le¡st 7¡ Lhe f¡ll depth below the footing. A representative of the geotechnical engineer should evaluate the fill placement for compaction and observe all footing excavåt¡ons prior to concrete placement. 5) 6) FOUNDATION AND RETAINfNC }VALLS Foundation walls and retaining struct"ures which are laterally supported and can be expected to undergo only a slight arnount of deflection should be designed for a lateral curth pressure computed CIn the basis of an equivalent fluid unit rveight of at least 55 pcf for backfill consisting of the cn-site fìne-grained soils. Cantilevcred retaining .structures which are separate from thc residence and can be expected to deflect sufñciently to mobilize the full aclive 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 pcl for backfill consisting of the on-site fine-grained soils. All foundation and retaining struclures should be designed for appropriate hydrostal¡c and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures tecommended above ilssume drained conditions behind the walls and a horizontal H.P*KUMAR Proiecl No. 17.7.391 -6- backfill surface. The buildup of water behind a wall or an upward sloping backlìll surface rvill increase the lateral pressure imposed on a foundalion wall or retaining .strûcture. An underclrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least gA?a o{ the maximum standard Proctor density al. a moisture conlent ne¿¡r opti¡num. Backfill placed in pavcment ancl rvalkway areas should be compacted to at leasl957* 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 câuse excessive l¡teral pressure on the rvall. Some settle¡nent of deep foundation rvall backlill should be expected, even if the material is placed corrcctly, and could resr¡lt in distress to facilities constructed on the backfill. The lateral rcsistance of foundation or retaining wall footings rvill be a co¡nbination of the slicling resistance of the footing on the fou¡rdation materials and passive eârth pres.çr.rre against the side of the footing. Resislance to sliding at the bottonrs of the foorings can be calculated based on a coefficient of friction of 0.35. Passive pressure of compacted b¡ckfill against the sides of the footings can be calculated using an equivalent fluicl unit weighr of 325 pcf. The coefficient of friction and passive pressure vatucs recommended above âssr¡me ultimate soil strenglh. Suitablc f¿lctors of safety should be inch.rded in the design to limit the srrain which will occur at the ullinr¿¡te strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be cornpacted to a[ least 95Vo of llte maximum standard Proctor density ¿¡t a moisture content near optimum. FLOOR SLABS The nltural on-site soils, exclu.sive of topsoil, can be used to support lighrly loaded .slab-on-grade construction rvith a settlement risk similar to the foundation if the underlying soils are wettecl. We should ev¿luate the subgrade for expansive soils and the need for sub-excavation. To reduce the effects of some differential n'¡ovement, floor slabs should be separated from all bearing rvalls and columns with expansion joints which allow unrestrained vertical movernent. Floor slab controljoints should be used to reduce damage due to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be established by the deslgner ba.secl on experience H-PtKUMAR Proiect No. 17-7.391 -7- and the intended slab use. A minimum 4-inch layer of free-draining gravel should be placed beneath base¡nent level slabs to facilitate drainage. This material should consist of minus 2-inch aggregate with at least 507o rctained on the No. 4 sieve and less th¡n ZVo passing ¡he No. 200 sieve. All fill malerials for support of floor slabs should be compacted to at least gSVa of nlaximum standard Proctor density ât a moisture content ne¿¡r optimum. Required fill can con.çisf of the on- site soils devoid of vegetation and topsoil. UNDERDRAIN SYSTEM Although free water was nol encountered during our cxploralion, it has becn our experience in the area and where clay soils are ptesent, that local perched groundwater can develop during ti¡nes of heavy precipitation or seasonûl runoff. Frozen ground during spring runoff can crcate a perched condition. 'We recommend bclorv-grade construction, such as retaining walls and basemenl areas! be protected from wetting and hydrostatic pressure buildup by an underdrain systen. An underdrain should not be provided around slab-argrade garrge and crawlspace arcâs to help limit potential wetting of bearing soils from shallow wâler sources. The drains should consist of drainpipe placed in the bottom of the wall backfîll surrounded above the invert level with free-draining granular malerial. The drain should be placed at each level o[ excavation and at least I foot below lorvesl. ad.iaccnt lìnish grade and sloped ¿rt a minimum l%a to a suitable gravity outlet or sump and pump. Free-draining granular material used in the underdrain system should contain lcss than 2tlo plssing the No. 200 sieve, les.s than 507o passing the No.4 sicve and have a maxi¡num size clf ? inches. The drain gravel backfill .should be at least l'/tfeel deep. An impervious n¡embrane such as 20 ¡nil PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wctting ol the bearing soils. SURFACE DRAINAGE The lollowing drainage precâut¡ons should be observed during construction and maintained at all timcs after the residence has been completed: H-P{KUMAR Projecl No. 17-7-39'l -8- r)Inundation of the foundation excâvûa¡ons and underslab are¿s should be avoided during construction. Exterior backfill should be ndjusfed to near optimum moisture and compactcd to al least 954/o of the maximum standard Proctor density in pavement and slab areas and to at leasl 9AVo of the maxi¡num standard Proctor density in landscape areas. The ground surf¿ce surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimu¡n 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 wall backfill should be covered with filter fabric and capped rvith at least 2 feet of the on-site soils to reduce surface rv:rter infi I tr:ltion. Roof downspouts and drains should discharge well beyond rhe limits of all backfill, Graded surface swales should havc a minimum slope of 3tlo. Landscaping wl"rich requires regular heavy irrigation.should be located at least l0 feet from for¡ndation rvalls. Consideration should be given lo use of xcriscapc to reduce the potential for rvetting of soils below the building c¡Llsed by irrigation. 2) 3) 4) LIMITATIONS This study has been conducted in accordance with gcnerally accepted geoteclrnicalengineering principles and practices in this are¿¡ ¿rt this ti¡ne. We make no warranty either express or irnptied. The conclusions and recomnrendillions submitted in this report ¿¡re based upon the data obtained from the exploratory boring drilled al the location indicated on Figure l, the proposed type ol' construction and our expericnce in the area. Our services do not include determining the pre$encet prevenlion or possibility of mold or other biological contaminants (MOBC) developing in the future. Ilthe client is concerned about MOBC, then a professional in this special field t¡f practice should be consulted. Our lìnding.s include interpolation and extrapolation of the .subsurface conditions identified at the exploratory boring and variations in the subsurface conditions may not become evident until excavation is performed. Iiconditions encountered during construct¡on appear differenl from those described in this report, we should be notifìed so that re-ev¿luâtion of the recommendâtions may be made. s) H.PIKUMAR Projecl No. 17-7-391 -1¡- 'I'his rcport has becn plepared for the exclu.sive usc hy our client for design purposes. r#c are not responsible for tecltnical inlelpretations by others of our inforrnation. As thc project evolves, we should provide contin*cd consultalion and field sen'ices during constructio¡r to rcr.,iel,and monitor the implementation of our recommendations, and to verify tlrat the rcco¡nlnendations havc [:een appropriately interpreted. Significant design changes nray require additional analysis or modifications to the recomnlend:¡tions presented herein. We recommend on,sitc observatiolr of excavations and foundation bearing strata and testing of slruc¿ur'¿rl fîll by â represcnlative of the geotechnical engineer. Respcctful ly Subnrittetl, Louis E. ElleL Revieivcd [ry: Stcvcn L. Paq'lak, LEE/krc cc: Oddo Enginccring - ßob Oddo (tr!þ@cdclogrvs.conr) Ì{ H-PåKUMAR Projecl No. 17-7-391 LOT 64 P ¡Ñgnrls\'\w¡r 1 LOT 65 BORING 1 o ÀPPROXIMATÊ SCAL€-FÊET t7-7-391 H-PryKUMAR LOCATION OF EXPLORATORY BORING Fig. I ! âoRtNr r EL. 6204.8' LEGEND o n llLl; 5Al{0Y SILï AN0 CLAY WlTtl 6RAV[L, FIRM, SLIGHILY l{015f, 8R0WN. 5 tE/t2 11/t2 WC:5.6 g!=105 n ctAY (cL); 5|LTY, SÅRoy, VERY SfitF, SLtcHtLy l¡otsT, BR0|VN, Lot¡V PLÅSTICIIY. srLI ÀN0 clAY {ML-CL); SÀ}IDY, VIRY Sntf, sltcHIly M0|ST, UGHI ÊßolryN, cAtcÂRE0u5. SlLISr0Nl 88DR0C(; llt0lu',l HÂRO t0 ¡lAÊ0 UIH 0lPIlJ, SL¡CHIIY Morsl, u6HT GRÅY. EÅCLI VÄl.lÊy gVÂP0RtTt. 10 2t/12 WC:6,1 0D= I 07 -200=9 I þ IRIVE SAilPtf, 2-rNCr{ t.0. CÀUroRN|A Lil{Êt sAHpK. rqzr¡ I}RIVE SAMPII BL0W COUNï, H0lCÂftS ¡HAI 18 9L0WS 0l'-t '' A t4o-pouND HÁMMER rÂLl.tN6 l0 t¡¡cHls tryER[ R[QutR[o TO DRIVE THÉ sÅMPLTR I 2 INCHES. 15 2Ê/12 VIC:6.0 NOTES|-l¡J l¡Jl¡ IIFo- l¡Jê D0=107 1 rH[ txPr0RÀloRY s0R¡NÊ t'Ås 0R|LL¡0 0N t{Ây 16, 2017 l'/,rH Å 4-|NCH DrÀntTER C0NTTNUoUS tLroÌtl po|ltR AUGIR, 2A 28/t2 WC=t.5 D0:l l7 -200:60 2, THE IOCATION OI IHT TXPLORATORY BORINc WÅS IITASIIRID ÂPPROXIIIÂIÊLY. gY PACING FROM FTÂTURËS SHOWN ON 'H[ S¡¡T PtA¡¡ PROVIDÊ0. ]. THÉ TTIYÀTITN OF THE EXPLORÅTORY BORI',I6 TIÂ5 MTÂsUFTÐ BY HAND LTVTL AN} RTITR IO ROÅDI{ÅY GRAOÊ STAXT5. {. THt gxPtonÂIOBY 8ofiNe tocÅTtot'¡ Àrio tLtvÀTtori sHouLD 8E coNsrogRt0 ÅccuSAIr 0NtT I0 lr{t 0t6ntt tupltt0 gy Ît{Ë r4rTH00 usü). ?5 4t/t2 WC:5.4 00:1 08 5. TI{I TINIS ET]ì,ITTN ilAT¡RüLS SHOWN ON T¡{T IXPLORA1ORY 80R|NG toc FtPRtstNT Tl{t APPR0X|UÁII BoUNoÂRles Etrr{ft]¡ uÂItRrÂL TYPTS Àr'r0 lHt ¡iAt'¡stïtoNs ilAy Bt GRÀ0uÂ1. 6. CRûUN0WÅ¡IR WÅ5 NOT I|¡COUNIIRID lN ltlt 8OR|NC ÂI THt ïl'¡t 0r 0ntLUNc. 30 se/t2 7, LA8ÛftÂTORY 1T51 RTSUTTS: wc : lvAtÊfl c0filEt'ti tx) (Åsril Þ 2216); 00 = oRY 0iil51ïY {pct) (miu o tzr6); -200 = PtRCtNTAGt PÂSSINC ¡10. 200 SlEVt (ASI|'{ 0 ll10}. 35 1 7-7-391 H-PÈKUMAR LOG OF EXPLORATORY ÊORING Fig. 2 SAMPL€ OF: Sondy Silly Cloy FROM:Borlngt@5' WC = 5,6 ?{, 00 = 105 pcl ÂOÐITIONAL COMPRESSION UNDER CONSTÀNT PRESSURE ouE ro wETTtñc JJLJ3,tl I 2ê â :3otnzo{.) 1 0 -1 2 -3 *4 t ¡0 JJ l¡J3an I o)- (f J C)tt ()(J I 0 -l *2 -t PÉTSsIJß¿ - KST SÂMPLE OF: Sondy Slll ond Cloy FROM:Boring¡6t5' WC : 6,0 X, DD = 107 pcl t7-7-391 H-PryKJMAR S}YELL*CONSOLIOATION ÏEST RESULTS Fig. 3 H-P\KUMARTABLE 1SUMMARY OF LABORATORY TEST RTSULTSProject No. 17-7-391SOIL OR BÍDROCI(TYPISandy ClaySandy ClaySandy Silt and ClaySandy Silt and ClaySiltstone BedrockUNCONFNTDcoMPRËSStV€SIREN6THfP5FIAÎTÊR8ÊRG IIMITSPt^AsTtCINDËXt96lllourD UMITle6lPËNCENTpÂsstNG Ãto.2to stÊvÊ9l60GRADATION5ANO{%}GnAVn(%ìNATURALDRY DTNSTTY{pcf}r05107107lt7108NATURÂtMOISTUREC0NTÊttÎ{}615.6616.04.35.4SAMPTE TOCATIONDEPTHfftl510152025BORINGI