HomeMy WebLinkAboutSubsoil Study 05.12.2021ffi,tii l;.iii;¡,:i't fr¡ Jq¡,srr,,;iair,x" T$c;.': - ,.1:: : :, ,.,; ,:: .; ,. ,. it. ";,j . - ::- ,::j :, fli',:l i;i[';,rrn.1.;", :l.ii l,î]ål;;iìif5{)2t {ìounïy l{¡rad i54Clcnn'ood Springs, Cû 8160Iphone; {97{}) 945-7988fac: {s7{"¡) 945-8454crnail: kaglenwood@ku*ranrsa.ccnr,¿,. Ì,, l":' l'i', i: iü-),t,1 {";'*, i1*4: ;rj rr..L. (; t ì}'ûfiìce [.,ocatiolis: I]cnver {}lQ), Parkcr; Color"actro Sprirrgs, frort Co}lins. (ileuu,ood Spriegs, anri i}unrmit {)oun1¡, C*}oradoRECETVEDAU0 0 5 zoltGARFIELD COUNTYCOI¡IMUNITY DEVELOPMENTSUBSOIL STUDYFOR FOUNDATION DESIGNPROPOSED RESIDENCE7315 COUNTY ROAD 312GARFIELD COUNTY, COLORADOPROJECT NO.21-7-321MAY t2,2021PREPARED FOR:MATT RINGER7315 COUNTY ROAD 312I¡-EW CASTLE, COLORADO 81647
TABLE OF CONTENTSPURPOSE AND SCOPE OF STI'DY,.PROPOSED CONSTRUCTIONSITE CONDITIONS..FIELD EXPLORATIONFOUNDATION AND RETAINING WALLSFLOOR SLABST]NDERDRAIN SYSTEM ..............SURFACE DRAINAGELIMITATIONS...........FIGURE 1 - LOCATION OF EXPLORATORY BORINGSFIGURE 2 - LOGS OF EXPLORATORY BORINGSFIGURE 3 - LEGEND AND NOTESFIGURE 4 - SWELL-CONSOLIDATION TEST RESULTSFIGURE 5 - GRADATION TEST RESULTSTABLE 1- SUMMARY OF LABORATORY TEST RESULTS........-2 --1--4--5-.....- 6 --6--1--7 -SUBSURFACE CONDITIONS1FOUNDATION BEARING CONDITIONS1DESIGN RECOMMENDATIONS............... .....- 3 -FOUNDATIONSaJ-i{u.m¿r & Asso*åate*, ìnc, 6rFr*j*at ll}*. "Å1""1 "3f1
PURPOSE AND SCOPE OF STUDYThis report presents the results ofa subsoil study for aproposed residence to be located at7315 County Road 312, Garheld County, Colorado. The project site is shown on Figure 1. Thepurpose of the study was to develop recommendations for the foundation design. The study wasconducted in accordance with our agreement for geotechnical engineering services to MattRinger dated April 5,2021.A field exploration program consisting of exploratory borings was conducted to obtaininformation on the subsurface conditions. Samples of the subsoils obtained during the fieldexploration were tested in the laboratory to determine their classification, compressibility orswell and other engineering characteristics. The results of the field exploration and laboratorytesting were analyzedto develop recommendations for foundation types, 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 subsurface conditionsencountered.PROPOSED CONSTRUCTIONThe proposed residence will be a single-story wood-frame structure with a lower walkoutbasement level. Ground floors will be slab-on-grade. Grading for the structure is assumed to berelatively minor with cut depths between about 2 to 9 feet. We assume relatively lightfoundation 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.SITE CONDITIONSThe subject site was avacant pasture with a reclaimed well pad uphill of the building envelope.The ground surface was sloping down to the north/northwest at a grade estimated at around5 percent. Vegetations consists of grass.K¡¡mar & Åcsm*ìatec, ån*. IFruje*t I{*+. il'i "?"t?1
/)FIELD EXPLORATIONThe field exploration for the project was conducted on April 7, 2021. Two exploratory boringswere drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. Theborings 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 Kumar &Associates, Inc.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 penetration test described by ASTM Method D-l586.The penetration resistance values are 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 Logs of Exploratory Borings, Figure 2. The samples were returned to ourlaboratory for review by the project engineer and testing.SUBSURFACE CONDITIONSGraphic logs of the subsurface conditions encountered at the site are shown on Figure 2. Thesubsoils consist of about 1 to 2 feet of topsoil overlying very stiff, sandy clay to between 8 and9 feet deep where dense, very clayey sand and gravel was encountered down to the maximumdrilled depth of 21 feet.Laboratory testing performed on samples obtained from the borings included natural moisturecontent and density and gradation analyses. Results of swell-consolidation testing performed onrelatively undisturbed drive samples of the clay soils, presented on Figure 4, indicate low tomoderate compressibility under existing low moisture conditions and light loading and a low tomoderate expansion potential when wetted under constant light surcharge. Results of gradationanalyses performed on a small diameter drive sample (minus 3á-inch fraction) of the granularsubsoils are shown on Figure 5. The laboratory testing is summarizedin Table 1.No free water was encountered in the borings at the time of drilling and the subsoils wereslightly moist to moist.FOUNDATION BEARING CONDITIONSThe upper clay soils encountered in the borings to a depth of approximately 9 feet possessrelatively low bearing capacity and low to moderate expansion potential when wetted. TheKumar & Åesc*iaten, i*'n" 6'Froject Nn. ä'q"T"3?'l
a-t-underlying sand and gravel soils possess a moderate bearing capacity and typically lowsettlement potential. Footings placed on the upper clay soils will have a risk of movement,mainly if the bearing soils become wetted, possibly resulting in distress to the proposedresidence.At the proposed excavation depth, we expect the subgrade will expose both fine-grained clay andcoarse-grained sand and gravel subsoils. We recommend using a spread footing foundationsystem bearing entirely on the granular soils for support of the proposed residence. Clay soilsencountered at footing grade should be sub-excavated to expose granular soils. Footing gradecan be reestablished with compacted structural fill or extended down to the granular soils bydeepening foundation walls.Isolated piers for support of decks or roof overhangs will have a risk of movement if placed onthe upper clay soils. Isolated piers in clay soil areas should be placed on a minimum of 3 feet ofcompacted structural fill or extended down to underling gravel soils, such as with helical piers, toprevent distress to the supported structures. Provided below are recommendation for spreadfootings on natural granular soils or compacted structural fill. Helical piers are typically a designbuild system. If used, the helical pier design should be submitted for our review and approvalprior to installation.DESIGN RECOMMENDATIONSFOUNDATIONSConsidering the subsurface conditions encountered in the exploratory borings and the nature ofthe proposed construction, we recommend the building be founded with spread footings bearingentirely on the natural granular soils or compacted structural fill.The design and construction criteria presented below should be observed for a spread footingfoundation system.l) Footings placed on the undisturbed natural granular soils should be designed foran allowable bearing pressure of 2,500 psf. Based on experience, we expectsettlement of footings designed and constructed as discussed in this section willbe about 1 inch or less. Isolated piers for support ofdecks or roofoverhangsplaced on a minimum 3-foot depth of compacted structural fill should be designedfor an allowable bearing pressure of 2,000 psf. Based on experience, we expectmovement of piers designed and constructed as discussed in this section could beup to about 1 inch.Kurnar &;l$sc+íaïeu, in*, oPr*j**ì l{m. ä'1.?"üä1
42)The footings should have a minimum width of 16 inches for continuous walls and2 feet for isolated pads.Exterior footings and footings beneath unheated areas should be provided withadequate soil cover above their bearing elevation for frost protection. Placementof foundations at least 36 inches below exterior grade is typically used in thisarea.Continuous foundation walls should be heavily reinforced top and bottom to spanlocal anomalies such as by assuming an unsupported length of at least 12 feet.Foundation walls acting as retaining structures should also be designed to resistlateral earth pressures as discussed in the "Foundation and Retaining Walls"section of this report.The upper clay soils, topsoil and any loose disturbed soils should be removed andthe excavation extended down to the relatively dense natural granular soils. Theexposed soils should then be moistened and compacted. The proposed footingbearing level can either be deepened to the granular soils by extending foundationwalls or reestablished with compacted structural fill placed on the underlyinggravel soils.Structural fill can consist of the onsite granular materials devoid of organics andoversized þlus 6-inch) rock, or imported granular material such as CDOT Class 6road base. Structural fill should be compacted to 98 percent of maximumstandard proctor density at a moisture content near optimum. Structural fillshould extent laterally beyond the edges of footings at a slope of l/zhorizontal to1 vertical.A representative of the geotechnical engineer should observe all footingexcavations prior to concrete placement to evaluate bearing conditions.3)4)FOLINDATION AND RETAINING WALLSFoundation walls and retaining structures which are laterally supported and can be expected toundergo only a slight amount of deflection should be designed for a lateral earth pressurecomputed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consistingof the on-site soils. Cantilevered retaining structures which are separate from the residence andcan be expected to deflect sufficiently to mobilize the full active earth pressure condition shouldbe designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weightof at least 45 pcf for backfill consisting of the on-site soils.s)6)7)ffiurw¿r Ál Å'nsqclatsn. ln*" 'r'firoj*rut FJ*. f t "?"i!?'1
-5-All foundation and retaining structures should be designed for appropriate hydrostatic andsurcharge pressures such as adjacent footings, traffic, construction materials and equipment. Thepressures recommended above assume drained conditions behind the walls and a horizontalbackfill surface. The buildup of water behind a wall or an upward sloping backfill surface willincrease the lateral pressure imposed on a foundation wall or retaining structure. An underdrainshould be provided to prevent hydrostatic pressure buildup behind walls.Backfill should be placed in uniform lifts and compacted to at least 90% of the maximumstandard Proctor density at a moisture content near optimum. Backflrll placed in pavement andwalkway areas should be compacted to at least 95o/o of the maximum standard Proctor density.Care should be taken not to overcompact the backfill or use large equipment near the wall, sincethis could cause excessive lateral pressure on the wall. Some settlement of deep foundation wallbackfill should be expected, even if the material is placed comectly, and could result in distress tofacilities constructed on the backfrll.The lateral resistance of foundation or retaining wall footings will be a combination of thesliding resistance of the footing on the foundation materials and passive earth pressure againstthe side of the footing. Resistance to sliding at the bottoms of the footings can be calculatedbased on a coefficient of friction of 0.45. Passive pressure of compacted backfill against thesides of the footings can be calculated using an equivalent fluid unit weight of 375 pcf. Thecoefficient of friction and passive pressure values recommended above assume ultimate soilstrength. Suitable factors of safety should be included in the design to limit the strain which willoccur at the ultimate strenglh, particularly in the case of passive resistance. Fill placed againstthe sides of the footings to resist lateral loads should be compacted to at least 95% of themaximum standard Proctor density at a moisture content near optimum.FLOOR SLABSThe natural on-site granular soils, encountered below the clay soils, are suitable to support lightlyloaded slab-on-grade construction. The upper clay soils possess an expansion potential whichcould result in slab movement if the subsoils become wetted. Movement sensitive slab-on-grade(basement floor) construction should be avoided where clay soils are present. Slab-on-gradeconstruction may be used provided precautions are taken to limit potential movement and therisk of distress to the building is accepted by the owner. To reduce the risk of slab movement,structurally supported floors over crawlspace can be constructed or the clay soils can be removedto a depth of 2 to 3 feet and replaced as compacted structural f,rll.Kt¡ rylan å",&.*s*Ëint*$, lnÇ"'iiTsrcject fi*. ?1"T"fä1
-6-To reduce the effects of some differential movement, floor slabs should be separated from allbearing walls and columns with expansion joints which allow unrestrained vertical movement.Interior non-bearing partitions resting on floor slabs should be provided with a slip joint at thebottom of the wall so that, if the slab moves, the movement cannot be transmitted to the upperstructure. This detail is also important for wallboards, stairways and door frames. Slip jointswhich will allow at least llz-inches of vertical movement are recommended. Floor slab controljoints should be used to reduce damage due to shrinkage cracking. The requirements for jointspacing and slab reinforcement should be established by the designer based on experience andthe intended slab use.A minimum 4-inch layer of free-draining gravel should be placed beneath basement level slabsto facilitate drainage. This material should consist of minus 2-inch aggregate with at least 50%retained on the No. 4 sieve and less than 2o/o passing the No. 200 sieve.All fill 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 predominantly granular soils devoid of vegetation, topsoil and oversized rock.UNDERDRAIN SYSTEMAlthough free water was not encountered during our exploration, it has been our experience inthe area and where clay soils are present that local perched groundwater can develop duringtimes of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create aperched condition. We recommend below-grade construction, such as retaining walls,crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup byan underdrain system.The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded abovethe invert level with free-draining granular material. The drain should be placed at each level ofexcavation and at least I foot below lowest adjacent hnish grade and sloped at a minimum I%ofoa suitable gravity outlet. Free-draining granular material used in the underdrain system shouldcontain less than 2o/o passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have amaximum size of 2 inches. The drain gravel backfill should be at least TYzfeet deep.SURFACE DRAINAGEThe following drainage precautions should be observed during construction and maintained at alltimes after the residence has been completed:Kumar & f.rsçc*Ëateç, ln*" 'i'åïr*j*ct &l*" Í1"7"3ä1
7-1)Inundation ofthe foundation excavations and underslab areas should be avoidedduring construction.Exterior backfill should be adjusted to near optimum moisture and compacted toat least 95o/o of the maximum standard Proctor density in pavement and slab areasand to at least 90o/o of the maximum standard Proctor density in landscape areas.The ground surface surrounding the exterior of the building should be sloped todrain away from the foundation in all directions. We recommend a minimumslope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of3 inches in the first 10 feet in paved areas. Free-draining wall backfill should becovered with filter fabric and capped with about 2 feet of the on-site finer gradedsoils 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 least10 feet from foundation walls.3)4)LIMITATIONSThis study has been conducted in accordance with generally accepted geotechnical engineeringprinciples 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 obtainedfrom the exploratory borings drilled at the locations indicated on Figure 1, the proposed type ofconstruction and our experience in the area. Our services do not include determining thepresence, prevention or possibility of mold or other biological contaminants (MOBC) developingin 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 extrapolation of thesubsurface conditions identified at the exploratory borings and variations in the subsurfaceconditions may not become evident until excavation is performed. If conditions encounteredduring construction appear different from those described in this report, we should be notified sotbat 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 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 implementation of our recommendations, and to verifu that the recommendations2)s)it¡,:rn;rr å Ågssciate*" !riç" 6Prøj*ct Se'. ii'f "T-3?1
-8-have been appropriately interpreted. Significant design changes may require additional analysisor modifications to the recommendations presented herein. We recommend on-site observationof excavations and foundation bearing strata and testing of structural fill by a representative ofthe geotechnical engineer.Respectfully SubmittedJames H. Parsons, P.E.Reviewed by:L(n1ã2?2Steven L. Pawlalq P.JHPlkaccc: Hinge Architects - Kurt Camrth -
7315 COUNTY ROAD 312.:-.' : .r..:.'¡ ... :: r ì,''';ì iÌi,j{j:"l: ."'lì r:i'(,sBENCHMARK:TOP EDGE OF CULVERTEL. 1OO" ASSUMEDNOT TO SCALEFig. 1LOCATION OF TXPLORATORY BORINGSKumar & Associates21 -7 -321
Fig. 2LOGS OF EXPLORATORY BORINGSKumar & Associates21 -7 -321BORING 1EL. 95.5'BORING 2EL. 95.2'07/1221/1226/ 12WC=9.7DD= 1 0814/12tNC=12.7DD= 1 06J20/ 12WC=9.4DD= 1 06-2OO=9218/6, 23/61010F-tJLJt!I-Fo-LIÕ40/6, 50/ 4.5WC=8.5DD=117+4=10-200=5841/12WC= l 1.8DD=115-200=58t--TJt!l"LITF-ILt¡lô151544/ 1250/.252020so/12s5/122525qII
IIÊa¡RLEGENDTOPSOIL; CLAY, SLIGHTLY SANDY, SLIGHTLY SILTY, ORGANICS, FIRM, MOIST, DARK BROWN.cLAy (cL); SLTGHTLY SANDY, SLTGHTLY StLTY, SCATÎERED ORGANTCS, VERY STTFF, SLIGHTLYMOIST.ß?.4l¡çtrlh:¡4wsSAND AND GRAVEL (SC-GC); VERY CLAYEY, DENSE, SLIGHTLY MOIST, YELLOW, WEATHEREDsr LTSToNE/SANDSTONE FRAGMENTS.DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLEIDRIVE SAMPLE, 1 S/3-|NCH l.D. SPLTT SPOON STANDARD PENETRATTON TEST7712 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 7 BLOWS OF A 14O-POUND HAMMER.,.- FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.NOTES1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 7,2021 WITH A 4_INCH DIAMETERCONTINUOUS-FLIGHT POWER AUGER.2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACINGFROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY INSTRUMENT LEVEL ANDREFER TO THE BENCHMARK ON FIG. 1.4. 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.7. LABORATORY TEST RESULTS:WC = WATER CONTENT (%) (ASTM D2216);DD = DRY DENSITY (pcf) (ASTM D2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913);-2OO= PERCENTAGE PASSING NO. 200 SIEVE (ASIM D1r4O).Fig.3LEGEND AND NOTESKumar & Associates21 -7 -321
NIIFig. 4SWELL-CONSOLIDATION TTST RESULTSKumar & Associates21 -7 -3214òrSJJLJ=tr1Izotrô=oU)zo(J3210-1-21.0 APPLIED PRESSURE - KSF10100¡sJJLI=tnIzot-'ô=o(nzoo10-1-2-3EXPANSION UNDER CONSTANTPRESSURE UPON WETTINGISAMPLE OF: Slightly Sondy CloyFROM: Boring 1 @ 4'WC = 9.7 %, DD = 108 pcfEXPANSION UNDER CONSTANTPRESSURE UPON WETTINGSAMPLE OF: Slightly Sondy CloyFROM:Boring2@5'WC = 12.7 %, DD = 106 pcf1l--1 -ìn¡ñSwcllt6tcd, Thsnot h æpduéd,wilhout the wrjtten apprcvol of-4100
iSIEVÊ ÂNALYSISU.S. SANDARD SERIESI.-.-..,..-....\r-. .-..HYÞROMETER ANALYSISTIME READINGS610090ao706040302010oot0203040so60298090100tr.125ROFMCLAY TO SILTCOBBLESGRAVEL 1O % SANDLIQUID LIMITSAMPLE OF: Grovêlly Sondy Cloy32%PLASTICITY INDEXSILT AND CLAY5A%FROM:Boringl@10'Thesé tesl rosulls opp¡y only lo lhesomples which wer6 issl6d. Th6lcsllng r6port shôll ñol bê rrprcduc.d,exc6pl ln full, wllhoul lhe wrlttênopprovol of Kumor & Associol€s, lnc.SlôvG ondlysls lesllng ls p€rformôd înoccordqnce wlth ASTM D6913, ASTM 07928,ASTM C136 oñd/or ASTM Dlf,lo.COARSEFINEGRAVELMEDTUM ICOARSESANDFINEFig. 5GRADATION TESÏ RESULTSKumar & Associates21 *7 -321
i' ii::: : :.i. .tì , ::.t 1.'r:.!.:::.il t'ì::.,;::.i ti : ;.t.:r:¡:,,t,r.;:::: I r. rl,.'':::, : .:, : r :i iTABLE 1SUMMARY OF LABORATORY TEST RESULTSSOILTYPESlightly Sandy ClaySlightly Sandy ClayGravelly Sandy ClaySlightly Sandy ClayGravelly Sandy CIaylosf)UNCONFINEDCOMPRESSIVESTRENGT}ILIMITS(o/olPLASNCINDEXAT(ololLIQUID LIMIf925858PERCENTPASSING NO.200 stEVESAND(%)32GR(%)GRAVEL10lDct)NATURALORYDENSITY108106117106ll59.48.5t2.7I1.8Í,tolNATURALMOISTURECONTENT9.74710510(fr)DEPTH2BORINGINo,21-7-321