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Home My WebLink AboutSubsoil Study for Foundation Design 05.30.02H Hrpruorth-Pawlsk Gcolechnical, lnc. 5020 County Road 154 Glenwood Springs, Colorado 8ló01 Phone; 970-945-79EE Fax¡ 9f0.945.8154 hpgeo@hpgerltech.com Job No. lff236l May 30,2002 Rob Crawford 1201 Fir Avenue Rifle, Colorado 81650 Subject:Subsoil Study for Foundation Desigu, Proposed Crawford Residence, Parcel 394, lJlttFLanq Garfield County, Colorado. Dear Mr. Crawford: As requested, Hepworth-Pawlak Geotech¡ical, lnc. performed a subsoil study for design of foundatioru¡ at the subject site. The study was couducted h accordatrce lvith our ag¡eemen: for geotechdcål engineering serv¡ces to you dated May 22,2002. The daø obtained and our recommendations based on the proposed constn¡ction atrd subsurface couditions encountered are presented in this report. Proposed Construction: The pro¡rosed residence will be a single story manufacnued stn¡cture over a walkout basement level loçated on the site as shown on Fig. l. Ground floor will be slab+n-grade. Cut depths are expectd to range beween about 3 to I feet. Foundation loadings for this type of construction are ¡uisuncd to be relatively light and typicål of the proposal rype of constnùction. lf building conditions or foundation loadings are significantly diffe¡ent from those described above, we should be notified to re-evaluate the recommendations presented in this repon. Site Conditions: The site was vacant at the time of our field exploration. The ground surface in the building area is relatively flat with a gentle slope down to the north and about 2 ¡a 3 feet of elevation difference. A drâinâge borders the norrhern ponion of the property. Vegeation coosists of grass and weeds. Sagebrusb and cononwood trees are loc¡ted along the northcrn drainage. Subsurface Conditions: The subsurface conditions at the site were evaluated by observing two exploratory pits at the approximate locatious shown on Fig. l. Thc pits had bcen excâvatd prior to our arrival on-site. The logs of the pits are presentd on Fig. 2. The subsoils encountered, below about I foot of topsoil, consist of medinm stiff to stiff, sandy ro very sandy clay and silt. Results of swell-consolidation testing perforrred on relatively undisurbed samples of the silt and clay soils, presented on Figs. 3 ar¡d 4, generally indicate lorv to moderate compressibility under conditions of loading and wetting. The sample from Pit I at 3 feet.showecl a minor collapse potential Rob Ctawford May 30, 2002 PageZ (senlemeot under constant load) when wetred. No frcc water was observed in the pin at the time of excavation and the soils were slightly moist to moist. Foundation Recommendations: Considering the subsoil condirioas encountered in the exploratory pits and the nature of the proposed construcdon, we recommend spread foodngs placed on the uudisturbed nan¡ral soil designed for an allowable soil bearing pressure of 1,500 psf for support of the proposed residence. The soils teud to compress after wening uncler load and there could be some post-constiruction foundation senlement. The amount of senlement would depend on the depth and extent of subsurface wening and could be on thc order of I to 2 i¡ches. Footings should be a minimum width of l8 inches for continuous walls utd} feet for colum¡s. Loose and disrurbed soils encountered at the fou¡datiou bearing level within the excavation sbould be removed and the footing bearing level extended down to rhe undisturbed natural soils. The exposed subgrade should be moistened and compacted prior to placing concrete. Exterior footings should be provided witb adequate cover above their bearing elevations for frost protection. Placement of footings at least 36 inches below rhe exterior grade is typically used in üris area. Continuous foundation walls should be reinforced top and bonom to span local anomalies such as by assuming en unsupportd length of at least 12 fcet. Foundation walls acting ari retaining structures should be designed to resist a lateral earth pressure bassd on an equivalent fluid unit weight of at least 55 pcf for the on-site soil as baclcfill. Floor Slabs: Tbe natural oo-site soils, exclusive of topsoil, are suitable to supporr lightly loadcd slab-on-grade construction. The clay and silt soils are compressible when rvettd. To reduce the effects of some differential rnovement, floor slabs should be separatd from all bearing walls and columns with expansion joints which allow un¡esuained vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage cracking. Tbe requiremeils for joint spacing urd slab reinforcement should be established by the designer based on experience and the inænded slab use. A minimum 4 inch layer of freedraining gravel should be placed bene¿th basement level slabs to facilinte drainage and for subgrade supporr. This material should consist of mi¡us 2 inch agg¡egate with less than 50% passing the No. 4 sieve and less than 2% passing the No. 200 sieve. All flrll materials for support of floor slabs should be compacted to at least 95% of maximum standard Proctor density at a moisture conterit near optimum. Required fill can consist of the on-site soils devoid of vegetation and topsoil. Uuderdrain System: Although free water rtras not encountered during our exploration, it has been our experience in the area that local perched groundwater cao develop during times of heavy precipitation or seasonal runoff. Frozcn ground during spring runoff caû create a perched condition. We recommend below-grade construction, such H.P GEoTEcH Rob Crawford May 30, 2002 Page 3 as rctainiug walls and basement areas, bc protected from wening afid hydrosatíc pressure buildup by an underdrain system. The drains should consist of drainpþ placed in the bonom of the wall baclcñll su¡rounded above the invert level with frsÊ-d¡¿ining granular material. The drai¡ should be placed at each level of excavatiou and at least I foot below lowest adjacent frnish grade and sloped at a minimum 1% to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, Iess than 50% pæsing tbe No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least l7z feet deep. An impervious membrane such as 20 mi¡ PVC should be placed beneath the drain gravel in a trougü shape and anached to the foundation wall with rnastic to prevent wening of the bearing soils. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: l) Inundation of the foundation excavations and underslab areas should be avoided during construction. 2) Exterior backfrll should be adusted to near optimum moisture and compacted to at least 95Vo of the maximum statrdard Proctor density in pavement and slab areæ and to at least 9O% of the maximum standard Proctor densiry in landscape areas. Free-draining wall backÍrll should be cappd with about 2 îeet of the on-site, finer graded soils to reduce surface water inf¡ltr¿tion. 3) The ground surface surroundi¡g the exterior of the building should be sloped to drain away from the fouudation in all directions. We recommend a minimum slope of 6 inches in the fust l0 feet in unpaved areas and a minimum slope of 3 inches in the first l0 feet in pavement and walhvay ¿uea:i. 4) Roof downspouts and drains should discharge well beyond the limirs of all backfll. 5) Landscaping which requires regular heavy irrigation, such as sod, should be located at least 5 feet from the building. Limitations: This sn¡dy has been conducted in accordauce with generally accepted gcotechnical engineering principles and practices in this area at this time. We make no warranty either expressed or implied. Thc conclusions and recomneudations submitted in rhis report are based upon the data obtained from the exploratory pits excavated at the locations indicated on Fig. I a¡d to the depths shown on Fig. 2, the proposed type of construction, and our experience in the area. Our frndings i¡clude interpolation and e.rtrapolation of the subsurface conditious ideutified at the exploratory pits and variations in the subsurface conditions may Dot become evident until excavation is performed. [f conditions encountered during construction appefu different from those H.P GEoÍÉcH Rob Ctawford May 30,2002 Page 4 described in this rcPort, we should bc uotified ar once so re-evaluation of rhe recommendations may be made. This rçon hæ been prepared for the exclusive use by our client for design purposes.'lVe are not respouiible for technical interpretations by others of our intormaìion. ns the project evolves, we should provide continued consultation and fìeld services during constructíon to review and monitor the implemen¿arion of our recommendations, and tovgrify that the recommendations have bcen appropriately intcrpreted. Significa¡r desigu changes may require additional analysis or modificatio¡x to thã recomme]ndations preseDtd herein. lrVe recommeud on-site observation of excavations and fo'ndation bearing shata and testing of structural ñll by a represent¿rive of the geotechnical engineer. If you have any questions or if we may be of funher assistjance, please let us litow. Sincerely, HEPWORTH - PAWLAK L, INC. Jordy Z. Adamson f., Reviewed by: tu;r. Steven L. Pawlak, P.E JZAlksw anachments 29707 H-P Geo::cx APPROXIMATE SCALE1'- 60' .IRACT 398 PROPOSED REsIDENCE \\ lPrT2 l¡J? 5 tr¡ @ = PIT 1 t I I ì t PROPERW EOUNDARIES 102 361 HEPWORTH - PAWLAK GEOTECHNICAL, INC.LOCATON OF EXPLORATORY PITS Fig. 1 PIT 1 PIT 2 rcræ.3 0D-9ã tC-1t.1 D0-tOJ -2t0l.70 0 5 10 LEGENO: 0 ooE I Eôoê ibo¡! I E Aoo rc-t¡.5 0D-10Íl tþ-20.O O0-e0 -200-E:l JJ.Þ47 Pl-7 5 1o þ TOPSOII; sondy silt ond cloy, orgonlcs, sllghtly moist, brovn. CLAY ANO SILT (CL-ML); sondy to wry sondy, etrotificd, mcdíum stiff to stlff, moist, brom,lor plosticlty. 2' Diometer hond drlwn llnr somplc. NOIES: 1. Explorotory pita were Gxcowted prior to our slte vislt on Moy 22, 2OOZ, 2. Locotlons of €xplorotory plts r€rc msoqrred opproximotely by poctng from feoturcs on thc elte plon provldsd. 3. Bevotlona of êxplorolory plts ware not meosured ond logs of explorotory plts ore drown to depth.Plt 1 ls obout 2 to 3 fcct hlgher thon Plt 2. 4. lhg- cxplorotory plt locotlons should be considered occurotc only to the dagrec lmplled by thc mcthod used. 5. 'fhe llncs bettesn motariols shotn on the crglorotory pit logs reprcaent the opproxfmotc boundorles batween moterlol t¡pes ond tronsltlons moy be groduol. 6. No ftee wotcr wos encountcrcd ln the plts of the tlme of obserwtlon. Fluctuotlons in çot€r l€vel moy occur wlth timc. 7. Loborotory Testlng Results: tÍC=lYoterContcnt(Z) DD - Dry Dcnsity ( pcf ) -200 - Pcrccnt posslng No. 200 sievcLL=LiguidUmít(Z) Pt - Ptosticity tndcx ( Z ) 102 361 HEPWORTH-PAWLAK GEOTECHNICAL, INC.LOGS OF EXPLORATORY PITS Fig. 2 o N cg aht,o o, Eo C) 1 2 3 4 0.1 r.0 10 APPUÉO PRËSSURE - ksf 100 o N Ê1(',6 cto CL) Eo C) 3 1.0 10 APPIIED PRESSURE - ksf 100 Moisturc Content - '18.5 Dry Dcnsity - 1Oz Somple of: Sondy Silt ond Ctoy From:PitlotJFeet percent Pcf \I *ComprcselonuPon retting \) Moisture Contcnt : 23.3 Dry Density = 95 Somple of: Sondy Silty Cloy From:Pit2otSFcct percent Pcf \N ) No movemenl uPon wetting ltIIt I 0.1 102 361 HEPWORTH-PAWLAK GEOTECHNICAL, INC SWELL CONSOLIDAÏON TEST RESULTS Fig. J Moisturc Contcnt = 19.1 Dry Denaity = 103 Somple of: Sondy Silty Cloy From: Pît 2 ot 7 F¿et percont pcf No movcrnent uPon wctting \ \ I , 0 N c .Egtoð Ê 5() 1 2 3 4 10 APPUED PRESSURE - ksf 0.1 1.0 100 ro2 561 HEPWORTH-PAWLAK GEOTECHNICAL, INC.Fig. 4SWELL CONSOLIDATION TEST RESULTS HEPWORTH-PAWLAK GEOTECHNTCAL, rNcTABLE ISUMMARY OF LABORATORY TËST RESULTSJOB NO. l02'36Ìgort oRãf.Þnocx ftPE,tsandy silt and claysandy silty claysandy silty claysandy silty clayIrrrcofr¡FtNEocoMP¡tËs$tvEsr¡eNomIPSF¡ÂfTtn3€nG ufiilfsPt^Strct¡roExt*l7UOU¡OUMrft*¡27PÉâCTüTPASStilONO. 200srÍvc8370GFADATIONsÂt¡otitG¡r¡v€rn¡tf{AIUnÂronYoFt¡stfvIrcll1029995103NAfUIIÂLM(TSIUFEcoiltÉ¡¡flar18.520.o23.31I1sÂMPr€ tocÂftoñ¡ocPllrI f..ll3557aìt12