HomeMy WebLinkAboutSubsoil Study for Foundation Design 03.11.2011t (iji¡
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Brctt Beawrx aml laurn ltatten
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Subjecl:Subsoil Study hr Foundatfuir Dsign" Prn¡nsed Residence' [-ot M-4"
Mfrllarxl Point, ?82 Midland Foint Road, Carfieltl County, Cok¡rado
Ds¿r Gcntlcman:
Às rct¡ucstc{ Heprwrth-Fa$rlak GeoteJuricnl" Inu perbnned t $uh!CIil study for dcsigtl
of fouxlations at the subjcct sitc. The study rvas aoftduated in acmrdurce lv¡th cur
agtcemeilt for geotelrnical o.ngineering services to Brdt Beavers dated Odober 29, 201CI
arrd revisd February ?4 201 I . The datu obtained and our resDmürerdatbns bnsd on the
proposed qrrnt¡ucti<ur arrd sul¡aurfaæ conditions cncounterql are prmented i¡r tl¡ls rqx'ut"
Evaluatin¡r ofpotential geobgic lraza¡d inrpacls on tl¡c site ale be¡rotxl thc sm¡reofthb
study.
Prnposert Constlr¡etion: Thc proposed resitlwce rvill trc one arxl tnro $ory nmocl franrc
mnstmctk¡n rvith an attad¡ed garÐge nnd gurerally krcatd on the site as strcrvn orr lìþrc
l. Thc ktrver garder level bnsenrent {loor arxl gärqgc thor rvill bæ slatron-gnnde. (l¡t
rtqlths are e.x¡rccld to range bdrvee¡¡ about 4 to 6 M. Foundetion loadingp fur this type
of constructftrn are assu¡red to be relatirrely light srKI t)'picål of tlrc pro¡msd type of
construction.
If building conditions en bundatùo¡l kmdings are siguilicantly diflbent fiu¡¡r tlmse
tlcscribed abovg n"e slmuH be notifid to re-evahtatc the recorluncndatblts prwcrrted iü
this report.
Sitc Couelitions: I'tre propcrty wrus roacant ofsttt¡cturss and had lutthy stutw ctlvcr at the
tirne ofour tietd exptoration Tlre site is l,ocatcd irr the vnlþ bottom r¡f thc Roaring Fork
Rivrr and tlre ground surhee appeans to have gra<letl tturing stlbdiroision tlerrehpmurt
w"ith minor cnts ard fill. Vegctation on tlre site mnsists ofgrass and rveeds" Thø gmund
surftrcr is rplntivcly flat in tlre ñont and rcar ¡xrts of thc sitc rvith a rtry slrx:p
ernbo¡rknmr¡t trc¡dùrg northrvcst t<¡ soutluust &c{oss the ce¡rts ¡rortion of thc ¡xnputy.
A$orrdtmctl irrigatbn ditc-tres hal'c been mostly backnücd atd al4mruilly musstrl thc lot
irr tlre stcqr elnbn¡*nrent area, A, snul! ¡rcrd is bçrted about ?00 k{ rvrol of the site arxl
the Roaring tsork Rlvct ahout ?50 {i:ct cast of the propnty" Eagle Valley Eruporite
Fannalior¡ bcldrock is ex¡xrscrl on the vnlley side to tEre n'cst"
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Subsidence Potential: The Midland Point Subdivision is underlain by Pennsylvania Age
Eagle Valley EvaporÌte bedrCIck. The evaporite contains gyp$um deposits, Dissolutionãf
the g¡psum under certain conditions can cause sinkholes to develop and ean produce
areas of localized subsidence. Duting previous work in the area, sinkholes were observed
in nearlry subdivisions and along County Road 109. Sinkholes were not observed in the
immediate area ofthe subject'lot during our exploration. Based on our present
knowledge of the sitg it cânnot be said for certain that sinkholes will not develop, In our
opinion, therisk ofgrountl subsidence at Lot M-2 ís low and similar to other lots in the
area but the owner should be aware ofthe potential for sinkhole development.
Subsurface Condifions: The subsurface conditions at the site rver.e ev¿luated by
excavlting thlee exploratorypits at the approximate locations shown on Figure 1. The
logs of the pits aro presented on Fþre 2. Thesubsoils eneountered, below abou t 1.tÁ to 3
feet of rnan-placed fill in Pits 1 and 3 and IY, feet oftopsoil in Pit I consist ofrelatively
dense slightly silty sandy gravel with cobbles and boulderc. A sandy clay layer was
encounteled in Pit 3 overþing the granular soils. Results ofswell-consolidation tasting
performed on a relativelyundisturbed sample of the sandy clay, prosented on Figure 3,
indicate low compressibility under existíng moisbure conditíons and tight loading ancl a
low collapse potontial (settlernont undcr constant load) rvhen wetted. ihe sampiu
exhibited moderate cornpressibility after wetting under additional loading. Results ofa
gradation analysis performed on a sample of the natural sandy gravel (minus 5 inch
ûuction) obtarned û'orn tbe site are plasented on Fþre 4. No ûee water rvas obsorved in
the pits at the time cf excavation and the soils were slightly moist to moist.
Foundntion Recommendations: Considering the subsoil corulitions encountered in the
gxpl_oratory pits and the naturc.of the proposed conshuction, rve recommend spr.ead
footings placed on the undisturbcd natural granular soil designe<l for an allowable soil
bearing pÌessure otåJsp-f fot support of the plopose<l residence. The man-placed fill
and sandy clay soils tend to comllress under load ätd should be removed folnbeneath
footing areas. Footings should bo a minimurn width of 16 inchos for continuous walls
and 2 feet for columns. Loose and disturbed soils, existing fill and sandy clay soils
encountered at the fbundationbearing level within the exsavation should be removed and
the footing bgaring level extended down to the unclistulbed natural granular soils,
Exterior footings should be provided with a(tequate cover above their bearing elevations
foråost protection. Plaeement of footings at-lèast 36 inches below the exterior grade is
t¡picallyused in this area. Continuous toundãÏffiÇãTisMüld bereinforced tof, ard
bottom to span local anornalies such as by assuming m unsupported length of af least 10
feet. Foundation walls actirig as retaining structures should be designedlo rc,sist a latsral
earth pressure based on an equivalent fluid unit weþht of at least 50pef for the on-site
soil as backfÏll. A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placer¡ent to evaluate bearÌng conditions,
Floor Sl¿bs: The naturul on-site soilg exclusive of topsoil, are suitablo to support lightly
loaded slab-on-grade construction. To re<luce the effeıts ot'some differential movem--ent,
floor slabs should be separated fronr all beartng walls and columns with expansion joints
which allow unlestrained verlical tnovoment. Floor slab control joints should be used to
reduce damage due to slrinkage cracking. The requirements for joint spaoing and slab
Job No.l l0 3994
cåFtecrt
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rcinfotcement should be established by the designer based on experience and the ùrtenderl
slab use. A minimum 4 inoh layer of ûee-draining glavel6'hould beplaced beneath
basement levsl slabs to facilitate drainage. This materjal should consist ofminus 2 inch
agglegate with less than 5A% passing the No. 4 sieye and less than}a/opassing the No,
200 sievo,
All fill materials for support of floor slabs should be compacted to at least g5% of
maximum standard Proctor density at a moisture content near optirnum. Required fill can
consist ofthe on-site gravel soils devoid of vegetatio4 topsoit and oversiz.edrock.
Underdrain System: Although free water was not encountered tluring our exploralion, it
has been our exporience in the area that local perched groundwatu cariCevetop during
times of heavypecipitation or seasonal nrnoff Ftozen ground during spring runotrJan
create a perched condition. V9'e recommend below-grade constructíon, suoh as retaining
walls and garden level basement &reas, bÊ protected fiom wettirrg and hydrostdic
pressure buildup by an underdrain system.
The drains should consist of drainpipe placed in the bottorn ofthe wall backfill
surrounded above the invert level with ûee-draining grûnular materiat. The drain should
be placed at each level of excavation and at least I frot below lowest adjacent finish
grade and sloped at a minimum lYo ta a drywelr or sump and pump, Free-draining
granular materiel used in the underdrain systern should òontaln bsl than z0lo passing the
No. 200 sievg less than 50% passing the No. 4 sieve and have a maxímum size of i
inches, The draÍn gravel backfill should be at leasf l% feet deep.
Surface l)rainage: The followng drainage precautions should be observqd during
constntction and maintained at all times after the resiclence has been cornpleted:1) Inundation ofthe foundation exoavations and undetslab aieas should be
avoided during construction.2) Exterior backfill should be adjusted to near optimummoisture and
compacted to at least 95Yoof flte maximum standard Proctor density ín
pavement and slab areas and to at least 90% ofthemaxìmurn standard
Proctor density in landscape areas. Free-draining rvall backfill should be
capped with about 2 feet ofthe on-sitq fìner graded soils to reduce surface
water infiltration.3) 'Ilhe ground surf¿ce surroundfurg the exterior of the building shoulcl be
sloped to drain away tom the foundation in all directions. lVe
rteornmend a minimum slope of 6 inohes in the first I0 feet in unpaved
arÊas ând a minimum slope of3 inches in the first l0 feet in pavement and
walkway areas.4) Roof downspouls and dlains slrould discharge well beyoncl the limits of alt
backfill.
Li¡nltations: This study has been conducted in accordance with generally accepted
geotechnioal engineering principles and practices in ttris area at this time. We make no
waranty eithø express or irnplied. Theìorrclusions and recornmendations $ubmitted in
this ïeport are based upon the data obtained û'om the exploratory pits excavated at the
Job No. I l0 3994
efftecfi
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locatitlru ir¡dicatetl on Figrue I ard to ttre de6tus shorvn on Fþure 2" ttrc pnrpnwt tgrc .¡fm¡utruclbn, and our ex¡rcrience in tlrc sreå. oursrvicns ¿o imt inchxüc-dcisrnining rtrepremcg ¡rrevcrrtkrn orpossibilityof nxrkl urotherbiohgical cCIntaminants (MOBCj
dcveloping in tlæ futura tftlrc clie¡rt is concernd ahout MoBc, then a proÈsshnal'in
this special field ofpradioestmuld be comultsl. our findings i¡rclutlc intcrpotatiton arxucxtrapolatkrn of tlrc subsurfnce mnditk¡ns identiñed at the c.iphrarory pits a¡xl rnruiatknn
fu the subsurfacrc corxli'tþns nray rmt beurnæ evident ur*il cxäratbn is perfornrd. Ifmnditbus enwuntM durirlg m¡rstruc{it¡n ¿ìppear diflircnr {iou¡ thosne describd in thisrclþd, rr¿c slrouH bc rc{ifid at ouce so re-evuluationofthe reænmrc¡rdatftrns nny bç
nrade"
This report has beenr preparad for the exclusive txe try our clie¡rt &r dçþ pur.¡roses. Wearc¡Klt respomible fur tæhniaal interpretatbrx by otlrux ofour inñrnration As thepmiect cvolves, rve stnuk! pmvide continued ct¡nsultatk¡n nn¡ ficltl se¡viccs duringconstruetfun to revierv a¡d nrronitor the irnplculeirtatio¡r ofo¡¡r req¡nu¡re¡xlations, oø t*verify tlmt the rcconrmendatbr¡s have bec¡¡ appro¡uiately interprcted" sþnificant dc$ignctnngæ may rquirc additional anaþis or nr.rd¡Rcatbrn to tlù rcmnrnrendatüonsprwnted he¡cin. lVc rnconrnre¡xl on-sitcobservatior¡ofcxcavatft¡¡u a¡nl fu¡rnd¡rtionbearing straüa a¡rd lwtirl8 ofstruduat Íill by a rqrrescntative ofthe geotechnical
enginccr.
Ifyou har"c any queståons or ifrvc nray he of frrxher æistarre, please lct us knorv"
Respecr fu I ly Suhr¡rittad"
PAWLAK CECITECI-Nü\üICAI* ll.ùe"
l¡ruis Eller
Revierwed by:
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Daniel E- l{ardin" P.Ë.
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Altachnru¡ts Fi$¡rB t -
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Fits
2 - LogsofBxploratory Fits
3 - Srvell-C.or¡mlidation Test Results
Figure,å - Grdatbn "t'cst Rt'sults
"l-atrle I * Sumrnrary uf l-abt¡r*tory Testing
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PROPOSID I-O1' L AYOLJ I
r10 g$)A -ffi LOCATION OF Ð(PLORATORY PITS FIGURE 1
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Fltl-; sar,dy chy ed bordde{s, rrozen ån tpper t2 b rg kdrcs. nftor det,b.
TWnj wdy sil$ dry. nnecnwn st¡lf" digt üy fix,lst" b¡owr.
ctAY (ct); sty. sr.dy. uith gravd, ne*¡rn s&ff to slrl[ sftgtw nrcì¡sr" brcfi{*.
q¡$ÆL (GF-GM); sdtdy" d¡gÛrttr sllty. un:tlr dbtus ard boddees r.p to z @ h $ze h Fils I arìd g, derise,dbtrüyflr*t bror¡n
nda¡udy mffisH 2-öncf¡ <fp¡rneter eur sailWb.
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Ì{OTES:
1- Exphratory¡r*ts weexcarrded on February 24" ãll1 wittr a nù*rc¡.ca'dor.
2' Loc€ü¡orEoteeplolatcyptsnmrenwrulapprodnatdybypqcårgfroqnharr.nesstm¡¡onttrosüep6'lpro*led.
e Ehdkr$ d e¡@rdqy püs we obtaùned-byùderpohlier¡ betr¡reen cor*urs sû¡om¡r w¡ tho sfte o¡*r pro,&ld a.dffied by hrd bjd. togs are cha¡¡r, tCI d{h. --
* rheeç¡or*oryrxf tøiorpry¡dderødk¡nssmddbeoorxrilleredamratêorúytottcdbgreeürÐredbry$.ænretllod
used.
s" The Tr¡es befrrenrr rpfterifds st¡cnm on t'teelçrhre*rxy Frût kros refuasef* the a¡ryxminnte rxryrh[ftìs het*ee¡rmater¡dtypesa*dlraxmfunsn¡aybegrdd{i' ú -'r'-
6" f{o freB umder \4æ eflæw[ered h tte püts at ûre llne ol qcaratirg- FfudrHk]n in wder h,d mry offirrìrufth rkne.¿ LfudoryT€slÈ€Resdts:
ldúC - WeüerGortent(%)tÐ -- ùy|My(pct, '
+{ = fìercer¡l ld¡dr¡ed on ti}e t-lo. 4 sÈew
-Z(XI - Fercert passt¡g f.¡CI- 200 $bve
r10 399A I LOGS OF Ð(PLORAIORY PIT$FIGURË 2