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HomeMy WebLinkAboutSubsoil Studyiì{irlçi:ËË?'t*g:*.ÞVå,iqt : {;Ë*"} ä{:i=€ iË i{:¡'rl i ì.:;, i:'.'; ¡ !-; - l:';t-,',':,,i t ' lREG,Eflf EÐ:r.,,'.,i -¡r::'::.t l-i,.,,.rÌ : li-i ,'.: .. , -r ..i ,, ,,,,',..,,,'.,frl{R'Ï'4 2422 i',,'.,'.,],i.,r ì,'.QARFIELD COUNW r r : : r : i : ì : i :-,,.,,:ûO..]![Mü!tl lÏy, DEVELOPIIENT þ4, SUBSOIL STUDY FOR TOUNDATION DESIGN PROPOSED RESIDENCE LOT FW-8, THE FATRWAYS ASPEN GLEN GARtr.IELIT COUNTY, COLORADO JOB NO. tt4 22sA JUNE 30,2014 PREPÁ.RED FOR: CRAIVFORD DESIGN BUILD, LLC ATTN: SIMON BENTLEY PrO. BOX 1236 CaRB(}NDALE, COLORADO 81623 s ¡¡q g.$ r#ìÊ0 Stç i¡¿qÊ1$ et : : '! iì I : : 'II I 'ì I': : : t, i I ì ; j! iå-aii;r:r .:i*l-,941"?T ;ç e {--",.'i¿:;.:,j¡; S;-:ri:'e.1:- ?i:}-ti.,a5-55,.:,; * lirlvr,:r¡}:,"¡rp* i:t?t.}.,4{':¡j,l+:jt"- TABLE Otr'CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION......... SITE CONDITIONS SUBSIDENCE POTENTIAL ....... FIELD EXPLORATION............. 1 SUBSURFACE CONDITIONS J- FOUNDATION BEARING CONDITIONS,.... ........_ 3 - DESIGN RECOMMENDATIONS FOUNDATIONS."....... FOUNDATION AND RETAINING IMALLS FLOOR SLABS TINDERDRAIN SYSTEM SURFACE DRAINAGE .........,. 4- 4- 5- 6- 7- 7- LIMITATIONS.. REFERENCE FIGURE 1 . LOCATION OF Ð(PLORATORY PITS FIGURE 2 - LOGS OF EXPLORATORY PITS FIGURES 3 AND 4 - S}VELL.CONSOLIDATION TEST RESULTS .9- PURPOSE AND SCOPE OF STUDY This report presents the results of a zubsoil study for a proposed residence to be located at Lot FW-8, The Fairways, Aspen GIen, Garfield county, colorado. The project site is shown on Figure I ' 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 Crawford Design Build, LLC dated June 9, ZA14. Chen-Northern, Inc, (1991 and 1993) previously conducted preliminary geotechnical engineering studies for the subdivision development and preliminaryplat clesign. A field explorationprogram consisting of exploratorypits was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classification, compressibility or swell and other engineering characteristics. The results of the field exploration and laboratory testing were anallzed to dwelop recommendations for foundation t)ipes, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained. during this study and presents our conclusions, design recornmendations and other geotechnical engineering considerations based on the proposed construction and the subsurface eonditions encountered. PROPOSED CCINSTRUCTION The proposed residsrice wiil be a two story wood frame structure above a crawlspace with an attached garage. The garage floor will be slab-ou-grade. Grading for the structu¡e is assumed to be relatívely minor with cut depths between about 2 to S feet. We assume relatively light foundation 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 cont¿ined in this report. -2- SITE CONÐITTTNË The property is located cn üolden Bear and the pits were dug pricr to our site visit. Vegetation consists of grass and weeds. The ground surfaee is relatively fiat with a gentle slope clown tn tlle north*nofiheast ånd possiblypartly graded during the subdivision developrnent. Elevation cliffersnce aflûss the building ares is about two feet. Ths site is horder*d by a gclf eourse To the west {rear} and the k:t to the south is tleveloped with a two*stcry residence. SUBSIDENüE PTTENTIÁ,L The Aspen Glcn Subclivision is underlain byFennsylvania Agefragle Valley Evaporite bedrack. The evaporite eontains gypsum deposits. Dissolution of the gypsurn undcr cÊrtain conditions tan cause sinkholes to develop and canprcduce arcas ofloc¿iized sul¡sidence. During previous studies in the areä, several braad subsiclence arsas and smaller size sinkhals areas were observe<l seattcred t}:roughout the Aspen Gleir development, predominantly on the *ast side of the Koaring Fark River {Chen-N*rthern, hrc., 1993). A mapped sinkhole is located about 60ü fect north of this lot. Sitrkfrcles r¡''ere not abserved in t"hc immediate area çf the subjeet tot" Based on our present knowledge of the site, it oanr¡.ot be said for certain that sinkh+les will not deveiop. ln aur opinion, the risk of ground subsidence at Lot FtrVr8 tfu*ugh the serviCe tifb of thé residen{re ie low and similar to sther lots in the area but the c,u/ner should be aware of the potential för sinkk¡le develcpment. FIELÞ UXFLÛRATIÛN The pits were observed on June 9,2û14. Three exploratory pits had been excavated by pthers at the locations shown cn Figure 1 tc evaluate the pubsurface eaneliÈåcns. The pits were laggeet by a representative of Hepworth-Fawl¡¡k Geotechnical, Inc, Job No. l14225A eeRecr-t -J- Relativeþ undisturbed samples of the subsoils were taken by hand with 2 inch liners. The liners were driven into the subsoils at various d.epths and the depths at rvhich the samples were taken are shown on the Logs of Exploratory pits, Figure 2. The samples were refumed to our laboratory for review by the project engineer and tesfing. SUBSI'RFACE CONDITTONS Graphic logs of the subsurface conditions e,ncountered at the site are shown on Figure z, The subsoils below about 6 inches of topsoil/root zone consist ofmedium stiff, sandy silty claydown to the maxirnum depth excavated af 7 feet. Based on our experience in the are4 we expect that the clay overlies silty sandy gravel with cobbtes and small boulders at depths of 10 to 12 feet. Laboratory testing performed on samples obtained from the pits included nafural moisture content and density and swell-consalidation testing. Results of swell-consolidation testing perfonned on relatively undisturbed liner samples, presented on Figures 3 and 4, indicate low compressibility under existing moisture conditions and light loading with a Iow collapse potential (settlement under constant load) when wetted. The samples showed moderate to high compressibility under increased load.ing after wetting. No free water \ryas encountered in the pits at the time of observation and the subsoils were slightlymoist. FOT]NDATION BEARING CüNDITIONS The nafural soils below topsoiVroot zone are adequate for support oflightly loaded spread footing foundations with some settlement potential, The underlying dense silty sandy gravel subsoils have low settlement potential but at about lZ fætdepth are below expected excavation depths for the garà,ge and erawlspace. If a foundation bearing on the dense gravel soils is desred for a low settlement risk, we should be contacted for additional recommendations. Topsoil should be removed from beneath builcling areås. JobNo. ll42ZSA ce$tecrt -4- Our experience in the area indicates that the topsoil and any man-placed fill is relatively shallow but should be evaluated for support of slab-on-grade construction at the time of excavating. DE SIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory pits and the nature of the proposed construction, we recoürmend the building be founded wíth spread footings bearing on the natural clay soils. îhe design and construction criteria presented below should be observed for a spread footing foundation systern, t) Footings placed on the sandy clay soils shorild be designed for an allowable bearíng pressure of 1,500 psf. Based on experienc€, r¡¡e expect initial settlement of footings designed and constructed as discussed in this section will be about t inch or less. There could be about t/zto t inch of additional settlement if the bearing soils are wetted and precautions should be taken to keep the bearing soils dry. 2) The footinp should have a minimum width of 20 inches for continuous walls and 2 feetfor isolated pads. 3) Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for iÌost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this area. 4) Continuous foundation walls should be reinforced top ¿ind bottom to span local anomalies. Foundation walls acting as retaining stn¡cfures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining'Walls" section of this report. Job No. 114225A cåfrecrt -5- 5) The topsoil, existing fill and any loose or disturbed soils should o-e removed and the footing bearing level extended down to the undistwbed natural soils. The exposed soils in footing area should then be moistened and compacted. 6) A representative of the geotechnical engineer should observe all footing excavations prior to çonc,rete placeme,nt to evaluste bearing con¿itions. FOTINDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth preszure computed ón the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting of the on-site fine-grained soils. Cantilevered retaining structures which are separate from thc residence and can be expectcd to deflect sufficiently to mobilize the fu1l active earth pressure condition should be designed fbr a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 45 pcf for backfill consisting of the on-site fine-grained soils. All foundation ¿nd retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent fcotings, traffic, construction materi¿ls and equipment. The pressures recofitmended. above a¡¡sume drained conditians behind the walls and a horizontal backfill su¡face. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral prcssure imposed on a foundation wall or retaining struchne. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in unifonn lifts and compacted to at least 90% of the maximum standard Proctor density at a moisture content near optimun. Backfill in pavement and walkway areas should be compactcd to at least g5% 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 cause excessive lateral pressure on the wall. Some Jt¡b No. '114275Í\ -6- settlement of deep foundation wall backfill should be expected, even if the material is placed oortectly, and could result in distress to facilities consffucted on tha backfilt. The lateral resistance of foundation or retaining wall footings will be a combinatiop of the sliding resistance of the footing 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 calculated based on a coeffisient of friction of 0.35. Passive pressure of compacted backfill against the sides of the footings can be calcul¿ted using an equivalent fluid unit weight of 350 pcf. The coefficicnt of friction and passive pressure values recommended above asfllme ultimate soil strength. suitable factors of safety should be included in the design to limit the strain which will occur at the ultirnate strength, partieularly in the ca.se 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 at a moisture content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly ioaded slab- on-grade construction. There couldbe some potential for slab movement if the subgrade soils are wetted. Any existing man-placed fîll shoutd be evaluated for slab support at the time of excavation. To reduce the effects of some differential movement, floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage cracking, The require,ments for joint spacing and slab reinforcement should be establish"d by the designer bassd on experience and the intcnded slab use. A minimum 4 inch layer of free-draining gavelshouki beplacedbeneath basement level slabs to facilitate drainage. 'fhis material should consist of minus Z inch aggregate with at least 50% retained on the No. 4 sieve and less than l% passing the No. 200 sieve. l Job No. 114 -7 - All fill materials for support of floor slabs should be compacted to at least gyvo of maxímurn standard Proctor density at a moisture content near optimum. Required fïll can consist of the on-site soils devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our experience in the area that local perched groundwater can develop during times of heavy precipitation or sçasonal runoff. Frozea ground during spring runoffcan create a perched condition. We recommend below-grade consfir¡ction, such as retaining wafls and basement areas (if any), be protected from wetting and hydrostatic pressure buildup by an underdrain system. The proposed shallow crawlspace and garage slab-on-grade should not need a perimeter drain system provide that good surface drainage away from the house is maintained around the building perimeter. Where installed, the drains should consist of drainpipe placed in the bottom of the wall backfill stnrounded above the invert level with free-draining granular material, The drain should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum lYo to a suitable gravity outlet, sump and purup or drywell that extends down into the underlyiug gravel soils. Free-draining granular material used in the underdrain system should contain less than 2% passing the No.200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of Z inches. The drain gravel backfill should be at least l% feet deep. SURFACE DRAINAGE The fcllowing drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) lnundation of the foundation excavafions ând underslab areas should be avoided during conskuction. No. ll 4225A -8- 2> Exterior backfill should be adjusted to near optimum moisture and compacted to at least g5% of the maximum standard Proctor density in pavement and slab areas and to at least g0% of the maximum standard Proctor density in landscape areas. 3) The ground surface surrounding the exterior of the building should be sloped to drain qway from the foundation in all directions. we recommend a minimum slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the fîrst 10 feet in paved xeas. Free-draining wall backfilt (if any) should be capped. with at least 2 feet of the on-site soils to reduce surface water infiltratiou. 4) Roof downspouts and drains shoulcl discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least 10 feet from foundation walls. LIMITATTONS This study has been ûonducted in accordaace with generally accepted geotechnical engineering princþles and practices in this area at this time. We make no warîanty either oxpress or implied. The conclusions and recommendations zubmitted in this report are based upon the data obtained from ths exploratory pits exeavated at the locations indicated on Figure 1, the proposed type of construction and ow experience in the area. Our services do not include determining the presencg 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 pits and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction ıpFear different from those described in this rqlort, we should be notified so tJrat re-evaluation of the recommendations may be made. eåFtecrr -9- This report has been prepared for the exclusive use by our clier¡t for design purposes, Itr/e are not respònsible fcr technical interpretations by others cf,cur info¡matisn. As the pmject evoives, we should provide continued consultation and field services during construcfion tn review and monitcr the implementation of aur recommendationso and to Yerifu that the recommendations have lrean apprapriately inferpretecl, Signifieaffi design cha*ges may requirc additional analysis sr modifications tÕ the reeommendations presented herein' \Ë'e recammend an-site *hservation of excavatiaRs and foundation beariag skata and testing of structural fîllby a representative of the geotechnical engineer. RespectfuIly $ubmitted, FIEP\4/ORTH * F,{'WL.{K Daniel E. Hardin, P.E. Reviewedby: INC Steven L. Pawlale, P.E. DEHlksw KEFERENCE chen*Northern, fuc., 199r, preliminaty Geotechnieal Engineeríng study, praposed '4spen Glen l)evelapmeut, Garfierd caunty, color*dç, preparcd roraspen clurCampany, dated ÐecemberZt,lggl, Jab No. 4 llã.gZ, Chen-Northeri, Inc., !993, {ieoteehnícal Engineering SÍudyþr prel.iminary plat Ðesign,' ,4.spen Glen llevølopment, Gãrfreid county, cçlorada, prepare4 fcrÃspen GlenCompan¿ dated M*y Zg, lgF3, Job No. 4 lll g?.. z ,"'t.-jf f a '44443 JobNo.114225A ;i ! APPROXIMATE SCALE 1t' :20' LOï 7 I I I ./ LOT I I ¡$ bo' 601z / "d" I ,I L P¡T 1r 3 I \ \ -t 1 GOLF COURSE I I / GOLDEN BEAR /: 6û11 I I 1 601 LOT B o I 6071 ¿ GAFAGE PROPOSED RESIDËNCE PIT 2;I Figure 1114 2254 ELEV.= 6070.5' 2 ELEV.- 6071' PIT 3 ELEV.= 6070' 1 0 0 à (l) c)IL Ic g 0)tf c)d) TL I -c o-oo 5 WC=3.5 DD:87 WC=4.7 DD:108 10 10 LEGENÐ: TOPSOIL; root zone, sandy silty clay w¡th roots, organic, soft, slightly moist, dark brown. CLAY (CL); silty, sandy, medium stiff, slightly rnoist, brown. þ 2" Diameter hand driven liner sample. NOTES: "1. Exploratory pits wero sbserved on June 9, 2014. 2. Locations of exploratory pits were measured approximately by pacing from features shown on the site plan provided. 3. Elevations of exploratory pits were based on topographic lines on the site plan provided. 4. The exploratory pit locations and elevations should be considered accurate only lo tho degree implied by the method used. 5. The lines between materials shown on the explorâtory pit logs represent the approximate boundaries between material Wpes and transitions may be gradual. 6. No free water was encountered in the pits al the time of observation. Fluctuation in water level may occur with time. 7. Laboratory Testíng Results: Wt : Water Content (7d DD : Dry Density (pcf) 114 225A LOGS OF EXPLORATORY PITS Figure 2 Compression %o)l\)oæJo)åJN)oosN)o9booo'!-urmg-o3m(na)cflm¡FûË'q5 ãrËrB-U(uf,=-'nolP- l€'QËq,' äd=ó +gq ri€^æü)etttÐC)Ðooo:f,g'c ¿^to!¿o=(J -(oxoU)9.o5r\t\T](ocCDC^) Compression %(¡)sl.ùJ();:)oc:C)tlTrffttfrflmct)îhc3mtFøä q5 5iËuejoıorú :f{t c)tq;3ile ig!a rr.e-€Ëìıo13ooo:l€(D='(o