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HomeMy WebLinkAboutSubsoil Studyl-lcf u. t'r tit. [':¡t'i¡ k ('-ie,ir,rr l-¡ll ic,rl, I ¡ re- jl-i.ì,.'r r._ì-,r.rnr.i' Ìì¡,¡,:ì i i -ì (-ì l,: rrr'¡"r, I Sl-¡ i r¡t-::. t- r',1,:,r ¡il,r rj I tir-ì i l:'lr,¡¡re: -'l?r.ì"il.li ;ç¡ ¡;) HEPWORTH - PAWLAK GEOTECHNICAL l;r:.:: 9 rt-1-t).[ j -,i.1i I erìììì I : hiltt (:tr'l :¡..tt,.'r c,- li,i,.'iri Septernber 16,20Ag Walter and Margaret Topor 52039 Highway 6 Glenwood Springs, Colorado 81601 Job No. 109 266A Subject: Subsoil Study for Fou¡rdation Desþ and Percolation Test, proposed Residence, ÍÃt4, Glenwood Highlands, 607 Highlands Drive, Glenwood Springs, Colorado Dear Mr. and Mrs. Topor: As requested, Hepworth-Pawlak Geotechnica! Inc. performed a subsoil study and percolation test for foundation and septic disposal desigrr,s at the subject site. The study was conducted as part of ou ptoposal for geotechnical engineering senrices to you dated August I l, 2009. The data obtained and our recommenda-tions based on the proposed construction and subsurface conditions encountered are presented in this r.pó.t. Proposed Constn¡ction: The residence will be a two story wood ûame stn¡ctwe ovçr a walkout basement level located on the site as shown on Figure l. The basement and attached garage wilthaye slab-on-grade floors. Crrt deptlls are expected to range between about 3 to l0 feet. Foundation loadings forthis type of ónstruction are assumed to be relatively light a1d tpical of the proposed tlpe of corntrucrion. The septic disposal system is proposed to be located to the south of the residence. Ifbuilding conditions or foundation loadings are significantly different ûom rhose described abovq we should be notified to re-evaluate the recommendations presented in this report. Site Conditions: The lot is v¿cant and located on the southern downslope side of Highlands Drive. The ground surface appears mostly natural and has u rtrong slope down to the south at about l5o/o grade. The te¡rain becomes steeper to the southeai. Elevation difference scross the assumed building area is about tO feet and across the lot is about 50 to 60 feet. Vegetation consists of grass, weeds and sage brush with scattered pinion andjuniper trees. There is a shallow ditch along the southproperty line that was not flowing water at the time of our field exploration. There are existing residences on the adjacent Lots 3 and 5 Subsurface Conditions: The subsurface conditioru at the site were evaluated by excavating two exploratorypits in the building a¡ea and one profile pit in the sepic disposal area at the approximate locations shown on Figure f. fne iogs of the pitr *e presented on Figure 2. The subsoils encountered, below about I to lt/z feet of topsoil, H -2- consistd of stifi.sandy. sitlV claf with scattered gravel and cobbies. The sandy silty clay extended to the pit depth of 8 feet in Pit 2 mrdto depths of about 5 ftet in pit I nd Syz feet in the Profile Pit where mdium dense, very clayyy silty sandy graveland cobbleî wer€ €Nrcountered to the pit depths of I feet. Results of swell-consolidation tcsting performed on relativelyundisrurbed saurples ofthe subsoþ præentcd on Figures 3 and 4, indicate low compressibilityunder existing moisture ænditions and light tãøing ana moderate to relativelyhigh compressibilitywhen loaded after wetting. One samplð slrowed a mino¡ collapse potential and another sample showed a bwþansion potantial when wetted u4der a oonstant 1,000 psf surcharge. The laboratory test iesults are . sunmrarized in Table I. No free watcr was obscrved in the pits atihe time of excavation and the soils were slightly næist. Found¡tíon Bearing Conditions; Thc subsoils possess low bearing capacity and in general a moderate sdtlcmcnt potential. Lightly loaded spread footings bearing on the natural soils can be used for fawrdation support ofthe UuilOing with a risk of settlemcnt. The risk of settlement is primarily ifthe bearing soils become wetted and precautions should be taken to prevent wefting. Potential sources of wetting include sr¡¡face watsr ponding and exccssive irrigation near tbe building foundation, and utility line 1eaks. The low expansion potential encourrtered in one ofthe tested samples is considered an isolatcd condition and can be neglected in thç building foundation and floor slab designs. We shoutd firther evaluate ihe overall subgrade condition at the time of construction. A lower risk foundation altemative with respect to potential settlement is a relatively deep foundation system such as helical piers or screw piles. provided below are recommendatior:s fsr a spread footing foundation systern Ifrecommendations for hclical piers or srrew piles are desired, we should be contacted. l'tiund¡tion Recommendafions: Coruidering tbe subsoil conditions encor¡ntered in the e4ploratory pits and the natrue of thc proposed constructio& u¡e recommend the building be supported on spread footings bearing on the rurdisturbed natt¡ral soils with some risk äf settlement. The footings should be designed for an allowable soil bearing pressure of 1,000 psf The soils tend to mmpress afrer wetting and there corrld be some post- construction for¡ndation settlement. The settlements oould be up to about 2 inches and diffferential depending on the depth and extent ofthe wetting. Footings should be a minimum width of i8 inches for continuous walls and 2 feet for columns. Loosc and disturbed soils and existing fill encounfsred at the for¡ndation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural soils. The footing subgrade should then be moistened and compacted. Exterior footings should be provided with adequate cover above their bearing elevations for frost protecfion. Placement of footings at least 36 inches below the exterior grade is typically used in this area. Continuous foundation walls should be heavily reinforced top and bçttom to span local anornalies and better withstand the effects of some differential settlement such as by assurning an unsupported length of at least 15 feet. Foundation walls acting as retaining structures-should also designed to resist a lateral earth pressu¡e based on an equivalent fluid unit weight of at JobNo.1092ó64 <;å5æcn 3 least 50 pcf for the on-site soil as backfill. The backfill should not contain topsoil or oversized rocks. Floor Slabs: The natural on-sitc soils, exclusive oftopsoil, are suitable to support lightly _loaded slab-on-grade construction. There could be some slab settlement ifthåiubgrãde - becomes wetted as discussed above. To reduce the effects bf some differential movement, floor slabs should be separated from all bearing walls and colum¡rs with expansion joints which allow unrestrained vertical movcrn-ent. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirements øi¡oint spacing and slab reinforcement should be established bytfe designei based on expårience and the intended slab use. A minimum 4 inch layerof free-draining gravel should be placed beneath basement level slabs to facilitate drainage. fnis maierial should consist of minus 2 inch aggregate with less tlwr 50o/o passing the Ño. 4 sieve and less thanz% passing theNo. 200 sieve. All fill materials for support of floor slabs should be compactod to at least 95% of maximum standard Proctor density at a moisture content near optimurn Required fip can consist ofthe on-site soils devoid of vegetatior¡ topsoil and oversized rocks. Underdrain Systeml Although fiee water was not encounterd during our exploration, it has been our experience in the area and where clay soils are present thãt bcal ierchedgroundwater can develop during times of heavy precipitation or seasonal runoif Frozen ground during spring runoffcan also create a perched condition. We recommend below- grade constructiorl such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup bv * rurderdrain systern The drains should consist of drainpipe placed near the bottom ofthe wall backfill suroundd above the invert level with free-draining granular material. The drain should be placed at each level ofexcavation and at least I foot below lowest adjacent finish grade and sloped at a minimum I% to a suitable gravity outlet. Free-draining granular material used in the r¡nderdrain system should contain less than 2% passing ttt" No. ZOO sievq less than 50% passing the No. 4 sieve and have a maximum size ofl inches. The drain gravel backfill should be at least lYt feetdeep. An impervious membrane such as 20 ot 30 mil PVC should be placed beneath the drain gravefin a trough shape and attached to the for¡ndation wall with mastic to prevent wetting ofthe bearing soils. Sur{ace Drainage: Positive surface drainage is an important aspect ofthe project to prevent wetting of bearing soils. The following drainage precautions should bè observed during construction and maintained at all times after the rèsidence has been completed:1) Inundation ofthc foundation excavations and tmderslab areas should be avo ided during construction.2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% ofthe maximum standard Proctor density in pavement and slab areas and to at least 900/o ofthe maximum standard Proctor density in landscape area{¡.3) The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. we JobNo,1092664 eåeecrr recomm€nd a minimum slope of 12 inches in the first 10 feet in unpaved areas and a minimurn shpe of 3 inches in the û¡st l0 feet in pavennent and walkway arear¡.4) Roofdonrnspouts aad drains should discharge well beyond the limits ofall backfill.5) tandsgaping which requires regular heavy irrigation, such as sod, and sprinkler heads should be locatcd at least l0 feet ûom the building. Consideration shoub bc given to the use of xeriscape to limit potential wetting of soils below the building caused by irrigation. Percol¡tion Testing: Percolation tests were oonducted on August 25 to waluatc the feasibility of an infiltration septic disposal system at thc site. One profile pit and three percolation holes were dug at the locations shown on Figure l. Th; test holes (nominal l2 inch diametff by 12 inch deep) were hand dug at the bottom of shallow backhoe pits and were soaked with water one day prior to testing, The soils exposd in the prrcoLti*r, holes are similar to those exposed in the Profile Pit slmwn on Figure 2 andconsistcdpl-Tl{ of sandy silty claywith scattcred gravel to very ctayey-sitty sandy gravel and cobblEs in percolation test P-2. Results of a gradation ana nyArometer *uíyJ.r nn u disturb€d b-ulk sample ofthe sandy silty clay soils from the Profile Pit are provided on Figure 5. The usDA soil classification ofthe sandy silty clay is Loarn The percolation test results, prese,uted in Table 2, indicate percolation rates ranging from about 10 to 20 rninutes per inch. Long term acceptance rale (LTAR) of Loam roiti p"t the State of Colorado regulations is about 0.50 gallons pßr squâre foot per day. Based on the subsurface conditions encormtered and the percolation test results, the tested area should be suitable for a conventioual infiltration septic disposal system. 4 Llmitationsl This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. V/e make no warranty either expressed or implied. The conclusions and recornrnendations submitted in this report are based upon the data obtained ùom the exploratory pits excavated at the locations indicated on Figure 1, the proposed type of construction *A o* experience in the area. Ûur services do not include determining the presence, prevention oi possibüity ofmold or other biologicat contaminants (MOBC) developing in the fi¡ture. If the cüent is concernod about MOBC, tïen aprofessional in this special field ofpractice should be consultd. Our ñndings include interpolation and extrapolation ofthe subsurface conditions identified at the exploratorypits and variations in the subsurface conditions may not bccome evident until excavation is performed. If conditions ericotmtered during construction app€ar different ûom thosc described in this re,port, we should be notified ai once so re-evaluation ofthe 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 or¡r information, As thc project wolves, we should provide continucd consultation and field services during construction to review and monitor the implementation of our recommendations, and to veriff that the recommendations have been appropriatety interpreted. Significant design Job No. 1ffi266A cåFtecrr -5- changes mayrequire additional analysis or modifications to the recommendatiors presented herein. We recommend on-site observation of excavations and foundation bearing strata and testing ofstructural fill by a representative ofthe geotechnical engineer. If you have any questions or ifwe may be of fi¡rther assistance, please let r:s know. Respectfirlly Submitted, HEPWORTH.INC. David A. Young, Reviewed by: t s ,Ï*-ALE. DAYlksw attachments cc: Figure l, Location of Exploratory Pits and percoration Test Holes Figure 2, Logs of Exploratory Pits Figures 3 and 4, Swell-Consolidation Test Results Table l, Summary of Laboratory Test Results Table 2, Percolation Test Results J.L.H. Architects * Attn: James Harris (iharisfôjlharchitects.com) H-P Geotech silverthorne- Attn: Jason Deem rjdeem@hpgeotãòír.co¡q) JobNo.1092664 cåFtecrr APPROXIMATE SCALE;l'- 4O ¡lþ¡¡an*-#é \Driu"I*-.- ,- I -_".-l- I I I I I Plr r \."-\ LOTS (F.risling Røsidence) ,II \ \I LOTS (Exbüng Be¡ldenee)\ II I \ \1 \ItPtrzttI II \v\I \ I L t 1 \ t I P'11\ AP.2 ¡ I PROFILE PIT LOT 4 Ê E¡r¡ldngDidt E¡lü¡E Fer¡c¿ .a t3 Ðr PROPOSÉD RESIDENCE €otrcHt ANDS DRryE 1 09 2664 HEntrôËñ{-FlrrtÄr( GEotEcHiltcAt LOCATONS OF EXPLORATORY PITS ANO PERCOLATION TEST HOLES FIGURE 1 PIT 1 ELEV.-87 P¡T 2 ELEV-*74'ELÉV.=67' PIT 0 5 10 LEGEND: WC-7.5 DD-90 WC*9.8 DD-102 0 (¡, (I)l¡ I o_oô 5 ¡ J 0¡,f I ! o.c)o WC-7.4 DD*99 WC-7.2 DD-99 i4-0 -2ffi=67 10 w TOPSOIL; organ¡c siþ clay, slightly moist, brown, scatt€red gravel. ctAY (CL); silty, sandy, scattered graveland cobbles, stitf, slightly moist, brown, câlcareous strea,(s, uppø several feet porous. GRAVEL AND COBBLES (GC.CL); v€ry clayey, silty, sandy, medium dense, stighüy moist, lþht brown, calcareous, rocks are prlmarily angular limestone ffagments. 2'Diameter hand driven liner sample. Disturbed bufk sample. þ t:: NOTES: 1. Exploratory pits were excavated on August 1g, 2009 with a backhoe, 2. Locations of exploratory pitswere measured approximalely by pacing from features shown on the site plan provided. 3' Elevations of exploratory pits were approximated from contours shown on the site plan provided. The plt logs are drawn to depth. 4. The exploratory pit locatlons and elevations should be considered accurate onþ to the degree implied bythe method used. 5. The lines between materials shown on the exploratory pit logs ropresent lhe approximate boundaries between materialtypes and transitlons may be grdual. 6. No free water was encountered in the pits at the time of o<cavating. Fluctuation in water level may occur with time. 7. Laboratory Testing Results: WC : Water Content (Zd DD = Dry Denstty (pcf) +4 : Percent Retained on the No.4 Sieve -2@ : Percent Silt and Clay 109 266A LOGS OF EXPLORATORY PITS Figure 2 percent pcf Moisture Content - 7. Dry Density = g0 Sample of: Sandy Sitty Gtay From: Pit I at 4 Feet il )7 / \ /Compressíon upon wetting il\ \ \ \ \ \ \ ) 10 AFPLIED PRESSURE - kst IO 0 a Co u,(:t i¡)go. o(J 2 3 4 5 6 7 I I 1æ1.00.1 109 2664 SWELL-CONSOLIDATION TEST RESULTS Figure 3 Moisture Contenl - 9.8 porcent Dry Density = '102 pcf Sanple of: Sandy Silty Ctay with Gravet From: Pit 1 at8 Feet \-) \ /.No movement upon wetting \ \ ( 0.1 1.O 10 'r00 10 APPLIED PRESSURE - ksf APPLIED PRESSURE - ksf 0 òs co '-an cD Eo Eo C) 2 3 4 1 àe Lo thc(lto-x ¡.rJ I L .g(Í, v,(¡) L CL Eo() 0 1 2 3 1 Moisture Content : 7.2 Dry Density = 99 Sample of: Sandy Silty Clay From: Pit 2 at 4 Feet pefcent pcf ( ç \ ¿ { \ \ Érpansion upon wetting \ , rr 1001.00.1 4 109 266A SWELL.CONSOLI DATION TEST RESU LTS Figure 4 2¡l HR. 7 !fr o 45 MIN_ l5 MlN. NMËREADINGS U.S, ETA}¡DArcSEFIES #50 t30 *1a #8 CLÞAN SAUAßE OPE¡{Nffi 4 MIN. 1 MIN,#4 E8' u4 111? 3. 5.6. 8'100 s0 80 7A 60 50 & sCI 20 10 æ 30 ôl¡J ¡tOz. æF ¡¿.l É, f- 50zl¡,() É.lr¡e60 (,z îrttt fL l-zl¡Jþ É,l¡¡ù 70 60 90 100 10 0 .001 .00¿ .005 .00s .019 .Og? .074 .1OO .900 .600 1.18 Z.æ 4.7s D!{MEÍEÊ OF PABT1CLES IN MITIIMETEHS 9.5 19.0 12.5 .5 76.2 2ff¡ 127 û¡Y co8tE8 GRAVËL O %gqND 33 %srLT 44 96 CLAY 23 To LIQUID LIMIT %PI-ASTICÍTY INDFX YO FROM: Profile Pit at 4 to 5 Fe€t - E Àla8[l I tlæ USDA SOIL TYPË: Loam 109 2664 USDA GRADATION TEST RESULTS Figure 5 HEPI VORm'PAW,AK GBOTECHNICAL INCTABI.E IsUftüNAFf OF I.ABORATORT TElif RESULn;Job No, tO9 26áAsoltonffDnoo(ïtPESaûdy Silty ClaySady Silty Clay withGravelSandy Silty ClaySandy Silty ClayI¡amult@tç$ÞGffiPrg¡smmnFlrlPrSFtAÎTREERO TffitlPIASÍICIt{oExmUOUÍ)uttftftPE¡C¡TTSlLlltlDCIAY89rft{S|A¡Dt¡l116RAV!tlfl0NAn illDßYDÊXg¡rfocî90Itz99Iì{AilrnÂrfMEilJECOMENÍfil7.59.87.47.2samtErocÀnoNOEPTHIttl4E244-5PrfI2ProñIePit HEPWORTH-P AUULAK GEOTECH}IICAL, INC. TABLE 2 PERCOLATIOII TEST RESULTS JOB NO. t09 268A HOLE NO.HOLE DEPTH (rNcHEs) LEI{GTH OF IHTERVAL (tutil) WAÏER DEPTI{ AT START OF 11{TERVAL {tNcHES} TYATER DEPTH AT END OF II{TERYAL (rNcHË3) DROP II{ WATSR LÉ'I'EL (rHcHESl AVERAGE PERCOI.ATIOil RATE (twÌ{JtNcH} P-1 25 t t*tU.Vt n ßVt t Yt t 7r/t t/. 7t/t ,+h Vt lv,7V*r/t 7r/.7 tA 7 8/t tA trlt 6+t v P-2 u 5 9 tVt V. t2 t*7r/t +t 7r/t 7V.V2 TVt flà t/t 6+t 6r/t Vt 6r/t ít/t V2 írlt SU¡.U. 5U 5 u, P-3 ?t 5 relilled 6r/2 5tÅ t/, 10 5rá ír/t \t Sr/.4r/.ra tr/t 7 ,/t 7 6\t tlt 6+t $t/t tlt ít/t s+t V. Srlz 5 Y2 Note: Penoolaüon t¿st holes rere hsnd dug ín the bottom of backbæ pits and soaked on Augr¡st U, 2W9. Percohüon tests werc corduttCId on August 25, 2N by a rcpræentatlve of IIP Ceotcch. The average percolaüon rat€s wßre bCIs€d on the lâst three readingF of each tcst.