HomeMy WebLinkAboutSubsoil StudyK+rfGededmicat and l.Íäleri¡b EnEineenard Enrircune¡hl SientiskS020CountyRoad 154Glenwood Springs, CO 81601phone: {970) 945-7988fax: (970) 945-84#email: kaglenwood@kumarusa.comAn Employcg ûmçd Compony www'kumqrusa'cornOfice Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Spr¡ngs, and Summit County, ColoradoSUBSOIL STUDYF'OR FOUNDATION DESIGNPROPOSED RI,SIDENCELOT 56, FILING 2, PINYON MESAPAINTBRUSH WAYGARFIELD COUNTY, COLORADOPROJECT NO. 19-7-221MAY 6,2019PREPARED FOR:PMGC2, LLCATTN: RON NORMAN6300 RTGLEA PLACE, SUITE 900FORT WORTII, TEX,{S 76116rrnorman@sbcglobaLnet
TABLE OF CONTENTSPURPOSE AND SCOPE OF STUDY..,SITE CONDITIONSFIELD EXPLORATION........- 1 -a......- 3 -1......- 3 -......- 3 -......- 4 -......- 5 -5-SUBSURFACE CONDITIONS......FOLINDATION BEARING CONDITIONS..DESIGN RECOMMENDATIONS..FOIINDATIONS..........FLOOR SLABST'NDERDRAIN SYSTEMSURFACE DRAINAGE ................LIMITATIONS...FIGURE 1 - LOCATION OF EXPLORATORY BORINGFIGURE 2 . LOG OF EXPLORATORY BORINGFIGURE 3 - SWELL-CONSOLIDATION TEST RESULTSTABLE 1- SUMMARY OF LABORATORY TEST RESULTS.....- 6 -Kumar & Associates, lnc.Proiect No.19-7-21
PURPOSE AND SCOPE OF STUDYThis report presents the results ofa subsoil study for a proposed residence to be located on Lot56, Filing 2, Pinyon Mesa, Paintbrush Way, Garfield County, Colo¡ado. The project site isshown on Figure 1. The purpose of the study was to develop recommendations for foundationdesign. The study was conducted in accordance with our agreement for geotechnical engineeringservices to PMGC2, LLC, dated April 8,2019.A field exploration program consisting of an exploratory boring was conducted to obtaininformation on subsurface conditions. Samples of the subsoils obtained during the fieldexploration were tested in the laboratory to determine their classification, compressibiiity orswell and other engineering characteristics. The results of the fie1d exploration and laboratorytesting were analyzed to develop recommendations for foundation tn)es, depths and allowablepressures for the proposed building foundation. This report summarizes the data obtained duringthis study and presents our conclusions, design recommendations and other geotechnicalengineering considerations based on the proposed construction and the subsoil conditionsencountered.PROPOSED CONSTRUCTIONAt the time of our study, design plans for the residence had not been developed. The building isproposed in the area of the exploratory boring location shown on Figure 1, Similar to the otherresidences proposed in the development, we assume basement or below grade levels will not beconstructed. Grading for the structure is assumed to be relatively minor with cut depths between2 and 5 feet. For the purpose of our analysis, foundation loadings for the structure were assumedto be relatively light and typical of the proposed type of conskuction.When building loadings, location and grading plans are available we should be notified to re-evaluate the recommendations contained in this report.SITE CONDITIONSThe property was vacant at the time of our exploration. The boring was drilled within thebuilding area. The site is vegetated with grass and weeds and scattered sagebrush. The groundKumar & Associates, lnc.Project llo. 1W-m
1surface is relatively flat and slopes moderately down to the west with about 10 feet of elevationdiflerence across the building area.FIELD EXPLORATIONThe field exploration for the project was conducted on April 17 , 2019. One exploratory boringwas drilled at the location shown on Figure 1 to evaluate the subswface conditions. The boringwas advanced with a 4-inch diameter continuous flight auger powered by a truck-mounted CME-458 drill rig. The boring was logged by a representative of Kumar & Associates.Samples of the subsoils were taken with l%-inch and 2-inch I.D. spoon samplers. The samplerswere driven into the subsoils at various depths with blows from a 140-pound hammer falling 30inches. This test is similar to the standard penehation test described by ASTM Method D-1586.The penetration resistance values aÍe an indication of the relative density or consistency of thesubsoils. Depths at which the samples were taken and the penetration resistance values areshown on the l-og of Exploratory Boring, Figure 2. The samples were returned to our laboratoryfor review by the project engineer and testing.SUBSURFACE CONDITIONSA graphic log of the subsurface conditions encountered at the site is shown on Figure 2. T\esubsoils consist approximately 6-inches of topsoil, underlain by stiff, sandy clay and silt down to7 feet, underlain by medium dense sand and silt from 7 to 19 feet, and underlain by dense, siltyto very silty, sand and gravel with cobble down to 26 feet. The soils encountered in the boringare variable and generally similar to the soils encountered at other nearby lots.Laboratory testing performed on samples obtained during the field exploration included nafuralmoisture content and density, and percent fines þercent passing the No. 200 sieve). Swell-consolidation testing was performed on a relatively undisturbed drive sample of the silt and claysubsoiis. The swell-consolidation test results, presented on Figure 3, indicate lowcompressibility under relatively light surcharge loading and a low collapse potential when wettedunder consta¡rt pressure. The laboratory testing is summarized in Table 1.No free water was encountered in the boring at the time of drilling and the subsoiis were slightlymoist.Kumar&Associatæ, lnc.Projec{ l{o. 19-7-221
-JFOUNDATION BEARING CONDITIONSThe sandy silt and clay soils and silty sand soils encountered at expected shallow cut depth tendto settle when they become wetted. A shallow foundation placed on the sandy silt and clay soilsor silty sand soils will have a high risk of settlement if the subsoils become wetted. It will becritical to the long-term performance of the structure that the recommendations for surfacegrading and drainage contained in this report be followed to limit potential wetting of the bearingsoils. The amount of settlement, if the bearing soils become wet, will mainly be related to thedepth and extent of subsurface wetting. Settlement in the event of subsurface wetting could be Ito 2 inches and likely cause building distress. Mitigation methods such as deep compaction, adeep foundation (such as piles or piers extending down around25 feet below existing groundsurface) or a heavily reinforced mat foundation designed by the structural engineer can be usedto support the proposed house with a lower risk of settlement. Presented below arerecommendations for shallow spread footings and slab-on-grade floor bearing on compactedstructural fill. If a deep foundation or mat foundation is desired, we should be contacted toprovide further design recommendations.DESIGN RECOMMENDATIONSFOT,J}TDATIONSConsidering the subsurface conditions encountered in the exploratory boring and the nature ofthe proposed construction, the building can be founded with spread footings bearing oncompacted structural fill with a risk of settlement and possible building distress.The design and construction criteria presented below should be observed for a spread footingfoundation system.1) Footings placed on at least 3 feet of compactedstructural fill should bejlor an allowable bearins Dressure of 1,500 psf. Based on experience, we expectinitial settlement of footings designed and constructed as discussed in this sectionwill be about I inch or less. Additional settlement on the order of I to 2 inchescould occur if deep wetting of the subsoils were to occur.2) The footings should have a ryrinimum width of 20 inches for continuous walls and2 feet for isolated pads.Kumar & Associates, lnc.Projec{ No.1$,7-221
-4-3)Exterior footings and footings beneath unheated a¡eas should be provided withadequate soil cover above their bearing elevation for frost protection. Placementoffoundations at least 36 inches below exterior grade is typically used in this--rarea.Continuous foundation wails should be heavily reinforced top and bottom to spanlocal anomalies such as by assuming an unsupported length of at least 14 feet;Foundation walls acting as retaining structures should also be designed to resist alaterai earth pressure corresponding to an equivalent fluid unit weight of at least55 pcf.The topsoil and any loose or disturbed soils should be removed in the buiidingarea. Thenatural silt and ciay soils or siltysand soils in footing areas shouldbesub-excavated to at least 3 feet below design bearing level and to at least I%feetbeyond footing edges. The exposed soils in footing area should then bemoistened and compacted. Stnrctural fill can consist of the onsite silt and claysoils compacted to at least 98% of standard Proctor density at near optimummoisture content.A representative of the geotechnical engineer should conduct compaction testingduring structural fill placement and observe all footing excavations prior toconcrete placement to evaluate bearing conditions.4)FLOOR SLABSThe natural on-site soils, exclusive oftopsoil, can be used to support lightly loaded slab-on-gradeconstruction with a risk of settlement similar to that for spread footings. To reduce the effects ofsome differential movement, floor slabs should be separated from all bearing wails and columnswith expansion joints which allow unrestrained vertical movement. Floor slab control jointsshould be used to reduce damage due to shrinkage cracking. The requirements for joint spacingand slab reinforcement should be established by the designer based on experience and theintended slab use. A minimum 4 inch layer of relatively well graded sand and gravel such asroad base should be piaced beneath interior slabs for support. This material should consist ofminus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than I2o/o passingthe No. 200 sieve.5)6)Kumar&Ássociats, lnc.Projec{ lrlo 19-7-221
-5-All filt materials for support of floor slabs should be compacted to at least 95o/o of maximumstandard Proctor density at a moisture content near optimum. Required fill can consist of the on-site silty soils or a zuitable imported granular soil devoid of vegetatior¡ topsoil and oversizedrock.T]NDERDRAIN SYSTEMAlthough free water was not encountered during our exploratior¡ it has been our experience inthe a¡ea that local perched groundwater can develop during times ofheavy precipitation orseasonal runoff. Frozen ground during spring runoffcan create aperched condition. 'Werecorune,nd below-grade construction such as basement areas be protected from wetting andhydrostatic prffsure buildup by an underdrain system. Slab-on-grade areas and crawlspaces lessthan 4 feet deç should not be provided with an underdrain.Where needed, the drains should consist of drainpipe placed in the bottom of the wall backfillsurrounded above the invert level with free-draining granular lnaterial. The drain should beplaced at each level ofexcavation and at least I foot below lowest adjacent finish grade andsloped at a minimum lo/o to a suitable gravity outlet. Free-draining granular material used in theunderdrain system should contain less than ZYopassingthe No. 200 sieve, less than 50% passingthe No. 4 sieve and have a mærimum slz;e of 2 inches. The drain gravel backñll should be atlæstlYz feet deep. An impervious membrane such as 20 mil PVC should be placed berieath thedrain gravel in a hough shape and attached to the foundation wall with mastic to prevent wettingof the bearing soils.SURFACE DRAINAGEProviding proper surface grading and drainage will be critical to keeping the bearing soils dryand limiting potential forbuilding settlem€nt and distress. The following drainage precautionsshould be observed dwing construction and maintained at all times after the residence has beencornpleted:1) Inundatioa of the for¡ndation excavations and underslab areas shouldbe avoidedduring construction.2) Exterior backfll should be adjusted to near o,ptimum moisture and compacted toat least 95Yo of úe maximum standard Proctor density in pavement and slab areasand to at least 90% of the maximum standa¡d Proctor density in landscape areas.Kumar & Associates, lnc"ProjdNo.l*7'221
-6-3) The ground surface surrounding the exterior of the building should be sloped todrain awayslope of 12from the foundation in all directions. We recommeird a minimum4)areas and aminimumslope of 3inches in the first 10 feet in paved areas. Free-draining wall backfill (if any)should bc covered with filter fabric and capped with about 2 feet of the on-sitesoils to reduce surface water infiltration.Roof downspouts and drains should discharge well beyond the limits of allbackfill.Landscaping which requires regular heavy irrigation should be located at least 10feet from foundation walls. Consideration should be give,n to use of xeriscape torduce the potential for wetting of soils below the building caused by irigation.LIMITATIONSThis study has been conducted in accordance with generally accepted geotechnical engineeringprinciples and practices in this area at this time. '!V'e rnake no waranty either express or implied.The conclusions and recommendations zubmitted in this report are based upon the data obtainedfrom the exploratory boring drilled at the location indicated on Figure l, the propose.d t¡pe ofconstruction and our experience in the area. Our services do not include determining thepresence, preveirtion or possibility of mold or other biological contaminants (MOBC) developingin the future. If the client is concerned about MOBC, then aprofessional in this special field ofpractice should be consulted. Our findings include interpolation and extrapolation of thesubsurface conditions identified at the exploratory boring and variations in the subsurfaceconditions may not become evident until excavation is perforrred. If conditions encounteredduring construction appearto be different from those described in this report, we shouldbenotified at once so re-evaluation of the recommendations may be made.This re,port has been prqpared for the exclusive use by our client for design purposes. We ae notresponsible for technical interpretations by others of our information. As the project evolves, weshould provide continued consultation and field services during construction to review andmonitor the impleinentation of our recomme,ndations, and to veriff that the recommendationshave been appropriately interpreted. Significant design changes may require additional analysisor modifications of the recommendations presented herein. lVe recommend on-site observation5)Kumar&Associatæ, lnc.Projeci l'lo. 1*7-n1
-7 -of excavations and foundation bearing strata and testing of structural fill by a representative ofthe geotechnical engineer.Sincerel¡Kumar & Associates, lnc.Shane J. Robat, P.E.Project ManagerReviewed by:Steven L. PSJR/kaccc: F&Mr'!td.1,ÅKumar E Associates, lnc.Pq¡ecrilo.197-n1
Fig. 1LOCATION OF TXPLORATORY BORINGKumar & Associates\\tË1\\\\II\\{\'.\t.\'\\-1.I'...,.r\II\IIIIIIIIIIIoFJ\àI-)-IloIIlìIIt-T-I-\-oÈort:1..,1LtI\\LOTÞ\\I\\IìYI"4%r9tt ""t\\-tI\\57\I//LOT/I/III/,Il,/IIllI\,utLOT20APPROXIMATE SCALE-FEET19-7 -221 AÉ
ãFig. 2LOG OF EXPLORATORY BORINGKumar & AssociatesBoRTNG 1/s6EL. 5205',LE*AENÐ*0NNT0Ps0lL; 0RGANIC, CLÅY ANÐ SILT, SÀNDY, FIRM, MOlSl, BR0WN.l--8/12WC=8,10D= 1 00CLAY AND SltT (CL-ML); SÀNDY, STIFF, SLI0HTLY MO|ST, UGHTBROWN.-51o/12WC=5.1ÐD=95*?00=70SAND AND SILT (SM-ML); CÄLCARE0US, GRAVELLY, MEDIUMDTNST, SLIGHTLY MOIST, LIGHT 8ROWN.IEEw,:¿GRAVTL AND SAND (cM-sM); Sltll T0 vtRY $LrY WIIH C0BBLIS,DENSÊ, SLIGHTLY MOIST, 8ROWN,- - 10FiDRIVT SAMPLT, 2.INCH I.D. CÅLIFORNIÄ UNER SÅMPLT,23/12t-UUuI:cF-o-LJôDRtVt SÀMPLE, I 3/8-INCH l.D. SPUT SP00N STANDÂRDPËNTÏRATION TEST15sl12DRIVI SAUPLT BLOW COUNT, INDICATES ÏHAÏ E BLOWS OFA 140-POUND HAMMIR FALLING 30 INCHES WIRT RTQUIREDTO DRIVT THI 5AMPLTR 12 INCHTS.22/12NOTËSI. THE EXPLORATORY BORING WAS DRILLTD ON APRIL 17, 2019 WITHA 4_INCH DIAMITER CONTINUOUS FLIGHT POVÍTR AUGER.-¿v72/12WC=7.5DD= 1 08-200:582. THE LOCATION OF THE EXPLORAÏORY BORING WAS MTASUREDAPPROXIMATTLY BY PACING FROM FTATURTS SHOWN ON THE SIÍTPLAN PROVIDTD.3. THT TLryAÏON OF THT TXPLORÂTORY BORING WAS OBTAINED BYINTERPOLATION BETWTEN CONTOURS ON THE SITE PLÂN PROVIDED."" 2546/124. THT TXPLORATORY BORING LOCATION AND TI.TVATION SHOULD STCONSIDËRED ACCURATT ONLY TO ÏHT DEGREE IMPLITD BY THEMETHOD UsED._305, THE LINES BETWEEN MAÏERIALS SHOWI.I ON ÏHT TXPLORÀÏORYBORING LOG RTPRISENT lHT APPROXIMATT BOUNDARITS BTTWETNMATERIAL TYPES AND THE TRANSITIONS MAY BT GRADUAL.6. GROUNDWATTR WAS NOT TNCOUNTIRTD IN THI BORING ÄT THTflME OT DRILLING.LABORÅTORY TEST RESULTS:WC ; WÁTER C0NTENT (%) (ÅSTM D 2216);DD = DRY DENSITY (PCf) (ÀSTM D 221ô);-2OO = PERCENTAGE PASSING NO. 2OO SITVT (ÀSTM D 1140).19-7 -221 A
Fig. 3SWELL-CONSOLIDATION TEST RTSULTSKumar & AssociatesS,AMPLE OF: Sondy Silt ond CloyFROM: Boring 1/56 @ 2.5'WC = 8.1 %, DD = 100 pcfbilÌt-i_l,j'lf,-- 1--i-liADDITIONAL COMPRESSIONUNDER CONSTANT PRESSUREDUE TO WETTING0^-1àsj-zUJ=v)t--5z,()tr-re -+otz.oc:-5-6-7-8l0t0019-7-221 A
l(t tlþ¡ur & As¡oclaiac, lnc,Gaotachnlcal and Matorials Ëngineersand Ënvironmental So¡ontlstskum¡ruca.comTABLE 1SUMMARY OF LABORATORY TEST RESULTSProjec{ No. 19.7.22156Very Silty Sand and Gravel581087.52ASandy Silt and Clay70955.151008.12y,Sandy Silt and Clayt/s6Pt-ÀsTtcINDEXlolcl(%lLIOUID LIMÍTSÀtlDf¿)f,{}GRAVELDEPTHBORINGlülìUNCO}IFINEDCOMPRESSIVESTRENGTHLIMITSPERCE¡IÏpAsstNG ¡to.200 slElÆGRADATIONNATURALDRYDENSfTY{ocnlo/"1NATURALilorsïuREcot'tïEr'rTLOCATTO¡¡SOILTYPE