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Home My WebLink AboutSubsoil Studyi{€: {¡H 4 Hcpworth-Pawlak Geotechnical, Inc. 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970-945-7988 Fax:970.945-8454 email hpgeo@hpgeotech.com -ð3' HEPWORTH - PAWLAK GEOTECHNICAL April 23,2003 Crystal Springs Builders Attn: Larry L. Stangeland 1044ManStreet Carbondale, Colorado 8L623 RECEIVED sËF iJ 3 ?ütl GARFIELD COUNTY COMMUNITY DEVELOPMENT Job No. 103 251 Ð ¡ .4 s Subject: Subsoil Study for Foundation Design, Proposed glrngeland Residence, Lot M-16, Midland point, Garfield County, Coloradı Dear Mr. Strangelandl ...,.,.. .tAs requested, Hepworth-Pawlak Geotechnical, Inc. performed a subsoil study for design of foundations at the subject site. The study rvas conducted in a."or¿aoce *it¡our agreement for geotechnical engineering services to you dated April 2L,2003. Thedata obtained and our recommendations based otr tle proposed consïuction and subsurface conditions eicountered are presented in thiì r"port. srÞ l} .t a Proposed Construction: The proposed residence will be one to two story wood frameconstruction over a basement level. An attached garage is proposed at th; main level.The basement and garage floors will be slab-on-giad.] coidepths are expected torange between about 3 to 8 feet. Foundation lóadings for this fupe of conitnrctiou are assumed to be relatively light and typical of the proposed type of construction. If building conditions or foundation loadings are significaffly different from those d'escribed above, we should be notified to re-evaluãte the recomrnendations presented inthis report. I Þà .lð .t q¡ 4fi 0 \dl ; Site Conditions: Lot M-16 is located on Midland Point Road and was vacant ar rhe timeof our site visit. The ground surface in'the building envelope is relatively flat with aslight slope down to the \r/est. There is a steep slope abouti to g feet hgh aown toMidland Point Road from thb building envelope. Mioor overlor gradingias performed 'on Lot M-16 during development of the subdivision. Vegetatioo i^ späse ano consisted of grass and weeds. Subsidence Potential: The Midland Point subdivision is underlain by pennsylvania Age Eagle Valley Evaporite bedrock. The evaporite contains gypsu; deposits." Dissolution of the gypsum uuder certain conditions can cause sintùoles tı develop andcan produce ar'eas of localized subsidence. During previous work in the area, sinkholeshave been observed in the lower Roaring Fork vaÍÃy. Sint<holes were not observed inthe immediate area of the subject tot. The exploratión pits were trrntiuJv shallow, for Parker 303'84t'71I9 r Colorado Springs 719-633.5562 ¡ Silverthome 970.46g-19g9 q t t ü 'or" a t a -2- foundation design only. Based on our present knowledge of the site, it cannot be said for certain that sinlùoles will not develop. In our opiniou, the risk of ground subsidence at Lot M-16 is low but the owner should be aware of the po-tential for sinlüole development. Subsurface Conditions: The subsurface conditious at the site were evaluated. by excavating two exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, belıw about onefoot of topsoil, consist of about 2 feet of silty sandy gravel overlying sandy gravel with cobbles and small boulders. Rezults of a gradation analysis perforned 6¡ ¿ srmple of ..u !-d_Y gravel (minus 5 inch fraction) obtained from the site are presgnted on Figure 3.'¡{}')No free water was observed in the pits at the time of excavation and the soils were slightly moist to moisr. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placed on tåe undisturbed natural soil designed for an allowable soit bearing pr_es.sure of 3,000 psf for support of the proposed rðsidence. Footings should be a minimum width of 16 iuches for continuous walls and,2 feet for colimns. Loose and disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed naturalI soils. Exterior footings should be provided with adequate cover above their bearing: : elevations for frost protection. Placement of footings at least 36 inches below the , **, t*ltdor grade is typically used in this area. Continuous foundation walls should be i i iffi :"tf:** t9p and bottom to span local anomalies such as by assuming æ unsupporred lli iWì l,enqth of at least 10 feet. Foundation walls acting as retaining qtrucures should be lil l'Ëii] fes|sryd to resist a lateral earth pressure based on an equivalent fluid unit weight of at''r ¡ I least 45 pcf for the on-site soil as backfill. Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded s1aþ-on-grade construction. To reduce the effects of some ditrerèntial 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 requirements f.ri:"i",t. spacing and slab reinforcement shoutd be established by thã designerbased on experience and the intended slab use. A udniul¡¡n 4 inch tayer of frss-d¡¿ining gravel should be placed beneath basement level slabs to facilitate Oiainage. This material ,,'. should co¡sist of minus 2 nchaggregate with less than 50% pugsiog the No. 4 sieve r. ,,!, üd less thau 27o passing the No. 200 sieve. , .'r:, t e ¡ i¡i All fill materials for support of floor slabs should be compacted ro at leasr 95Vo ofl:'. t"***t standard Procior density at a moisture cotrtent near optimqm. Required fill" can consist of the on-site soils devoid. of vegetation, topsoil andoversized rock. o "i 1j I I & ¿ I Iå"¡r'l'ß"|1.. ili llliillr I þ" t ó i3- Ëp 9 t) u Job#ß325r eåFtecrr - {- underdrain system: Although free water was not encountered during our it has been our experience in the a¡ea that local perched.groundwater can developI rs q "ir during times of heavy precipitation or seasonal runoff. Frozen ground.duing spring runoff can create a perched condition. 'We recommend below-grade consüuction, such as retaining walls and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. The drains should consr.st of drainpipe placed in the bottom of the wall backfill , L surrounded above the invert level with free-draining granular material. The drain i, , " i i ,1,, ,i' 'shouldbeplaced.ateachlevelof excavationandatleast I footbelowlowestadjacent :i i ' ,'l I i ii I il;, .;" fiish grade and sloped at a minimum 1% to a suitable gravity ourler or dryweti. The I ] i: lt I ,i b4; soils at the site are suitable for drywells. Free-draining granular marerial used in the I ] ' ' I ', underdrain system should contain less than 2vo passragthe No, 2o0 sieve, less thau #Jr:::::' î'mïi 50% passing the No. 4 sieve aud have a maximum size of 2 iuchès. The drain gravel i ; lt'-' "' backfill should be at least lVz feet deep. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed:1) Inundatic¡n ofthe foundation excavations and. undersl¿b areas should be avoided during construction.2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95Vo of the maximum standard Proctor density in pavement and slab a¡eas and to at least 90% of the maximum standard Proctor density in landscape areas. Free-draining wall backfill should be capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration.3) The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in alt directions. we recommend a minimum sþe of 6 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in pavement and walkrray areas.4) Roof downspouts and drains should discharge well beyond the limits of all backfiIl. a si ¿. ûr w lt rì , t1. È F ì^ LÍmitations: This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warranty either express or implied. The conclusions and recommendations submitted in !þis lenorl are based upon the data obtained from the exploratory pits excavated at the locations indicated on Figure I and to the depths shor¡m on Figure 2, theproposed type ., of construction, and our experience in the area. Our findings include interpolatiotr and , extrapolation of the subsurface conditions identified at the exploratory pits and variations in the subsurface conditions may not become evident until Licavatiou is' performed. If conditions encountered during construction appe¿u different from those t a O "4 Iob #103 ?-51 cåeecrr JffifitrffiffiIffiffi 4 jirlr \-l ìl ¡b... described in this report, \¡ie should be notified at once so re-evaluation of the recornmendations may be made. Louis E. Eller Reviewed by: h This report has been prepared for the exclusive use by our client for design purposes. W'e axe not responsible for technical interpretatioos bt others of our information. Asthe project evolves, we should provid,e continued consurtation end field servic""ao.iogcoûstruction to review and monitor the implementation of our recommendations, and toveriff that the recornmendations have been appropriarely interprer.o- significant designs[anges may require additional analysis or modifications to th; reconnrendations ¡ ;i i i f:::_YlÏ*h. TVe recodmend on-site observation of excavatioor *ãää¿äioo i Ip ;:: bea|ng süata and testiâg of structurat fitl by a represenrarive of rhe groærnoi"¿---- , t ,. r €tr$ltrêef. iìi I i:t i.: If you have any questions or if we may be of further assistance, please let us know. Respecttully Submiued, HEPTVORTH . PA\ryLAK GEOTECHNICAL, INC. d ii, t: liil l,l ,l e ot: ai' a Daniel E. Hardin, P.E. LEE/ksw attachments: Figure 1 - Figure 2 - Figure 3 -Gradation Test Results Pits Logs of Pits ila ðI I Job #103 251 eeeecrr rìill iill fri iil APPROXIMATE SCALE' 1" =3O'LOT M-19 &rt I %LOT M-20 t l.rii :tiill il: i lrldl{:,ìr -¡> lllrlr.,,lI clI o' i ì. i LOT BOUNDARIES i'r- r---¿-ê¿-¿¿êt¿¿-Õ-¿ PIT 1 I COMMON AREA LOT M-16 BUILDING SETBACK PIT 2 I LINES a-¿n-) ¿¿¿------- LOT M-15 l-ntn POINT ROAD NIIDLAND J 103 251 HEPWORTH-PAWLAK GEOTECHNICAL, INC.LOCATION OF EXPLORATORY PITS Flgure 1 4 .aI e $ 4. a ta l,i 'i lr PIT 1 P|'t 2 0 0 oo L¡. I J 5 +Þ64 - i -2oo-B 5 ool¡- I -c CLoô 1 1 l l p ll 1 \; 'f0pSO¡t-; sondy sllt ond cloy, orgcnlc, flrm, moist, dork brown. ffi ffi GRA\EL (GM); silty. sondy, wlth scotterod cobbles, dense, sllghtly moist to moist, brown GRAVEL COBBLES AND BOULDERS (GM-GP); sondy, slightly silty, very dense, slightty moÍst, tightbrown, rounded rocks. I I Disturbed bulk somple. Ïti:;*"ry pits were excovoted on Aprit 21, 2o05 wtth o cot 420D bqckhoe. 2. Locotions ol explorotory pits were meosured opproxfmotely by pocing from building envelopc córncrsstoked ln the ficld. !t. Elevctions of explorotory pits were not meosured ond logs of explorotory pits ore drown to depth.Pit 2 is obout 1 1/2 feet lower thon Pit 1. 1. }'e explorotory pit locotions ond elevotions should bc considered occurote only to the degree impliedby thc method used. 5. The lines betwèen moteriols shown on the. explorotory pit logs represent the cpproximote boundoricsbetween moteriql t¡lpes ond tronsitíons moy be groduol.- 6. No free woter wos encountcred ln the pits of the time of excovoting. Buctuqtions ln woter levet moyoccur with time. 7. Loborotory Testing Results: t4 = Percent retoined on No. 4 sieve -200 = Percent possing No. 20O sieve HEPWORTH-PAWLAK GEOTECHNICAL INC.LOGS OF EXPTORATORY PITS Figure 2 fi'e , t Æ{ LrÊs ---------- E- ---- --- EE - E -- I-¡- t-¡-¡- ETE -r- ---- ---- _E ---- - --¡- l- a -- IUE RÉTUÑGS (I.ETN Sq'âRE OPEMI{G¡ o 21{5 3l+' t t/t !' so. I't@ ro 90 Ìii :r ii, lii iliri It I iiit,t 'ril t0 I 30 ,o :, s ô!U ¡þIe l¡Ju.::t- to z, l¡J() É,tr¡o60 602 øv, fL 60F zl¡, C) É,l¡J{o o' l:!, l 70 go a0 20 90 to lm o.0s .(m .æ5 .09 .ots .o:t7 .gr1 .t5(r J00 .600 1.18 Lß +75 9.312ı tg.o t7..5 762 ß27t 20¡t DIAMEÏER OF PARTICLES IN MILLIME'IERS cl.AY 10 glf offi¡!¡ GRAVEL 64 %SAND 28 %SILT AND CLAY 8 % LIQUID LIMIT %PLASTCITY INDEX d,o SAMPLE OF: Slightly Silty Sondy Grovet wíth Cobbles FROM: Pit 1 ot 4 thru 5 Feet cotPsE 103 251 HEPWORTH-PAWLAK GEOTECHNICAL, INC.GRADATON TEST RESULTS Figure 3 b