The URL can be used to link to this page

Home My WebLink AboutSoil Report 04.25.2018Jtrly 25,2A13 RECEIVEÞ Apf{ "ì,5 ?.9tr9 GARFIELD COUNTY COMMUNITY OEVELOPME¡{T Mike Tande ¡r1i :tt iíi,:'l(¿.iri ti li;,i:1,,i;i ¡¡r, Sulrject Job No.ll3 223A subsoil study fbr Foundation Design, Proposecl Resiclence, Lot 83, Aspen Eqr"restrian Estates, 30 Equestrian way, Garfield courlty, coloracro Dear Mr. 'fancle: As requestecl, Hepworth-Pawlak Geotechnical, Inc. ¡rerformecl a subsoil str"rcly fbr design of foundations at the subject site. The study was conclucted in accorclance with our agreenrent fbr geotechnical engirreering services to you dated June 19,2013. The elata obtained and our reconunenclations basecl on the proposed construction ancl subsurface conditions encountered are presented in this report. Proposed Construction: The proposed residence will be one story woocl fiame construction with an attachecl garage. Grouncl floors willbe slab-on-gracie. The reside¡cewillbtlilt in the fi'ont parl of the lot ancl the site is shown on Figure t. Cut depths are ex¡rected to rallge between about 2 to 4 fbet. Founclation loadings for this type of construction are assulned to be relatively light and typical of the proposecl type of construction. It'builcling conclitions or fbunclation loaclings ale significantly different fi.om those clescribed atrove, we shoulcl bc notiliecl to re-evaluate the lecolrunenclaticurs presented in this reporl. Site Conditions: The property is vacant of structures ancl vegetatecl with grass ancl r'veecls. The site is locatecl on the Roaring For"k Valley trottorn ancl the 100 year fìoocl line fbr Blue Creelc is located about I00 fbet behincl (south oÐ the properfv. The grouncl surfäce is lelatively flat with a slight slope clown to the south. Subsiclence Potcntial: Aspen Equestrian Estates is r-uiclerlain tly Pennsylvania Age Ëagle Valley Evaporite bedrock. The evaporite ceintains gypsum deposits. Dissolution of the gypsuln uncler certain conditions can cause sinkholes to clevelop ancl can ¡rrocluce areas of localizecl sttbsiclence. During previous studics in the area, severâl brclacl subsiclence areas artd slnaller size sinklioles have been observecl scattered throughout the lower Roaring Fork Valley, Sinlchclles were not observccl in thc immediate area of the subjecL lot. Thc explclratory pits were relatively sl'rallow, fur'ttrunclation clesign only. Basc,l o,', ou, presetrt l<nowletlge of the site, it carurot be saicl for cer"tain that sinkholes will not clevelop. In our otrrinioti, tlie risk of grouncl subsiclence at Lot E3 tlrloughout the service liib of the ,lr: I building is low and similar to other lots in the area but the ou'n€r should be aware ofthe potential for sinkhole developrnent. Subsurface Condltlons: The subsurface.conditions at the site were evaluated by gxcav4ing two exploratorypits at the approximate locations shown on Figure l. The logs of the pits are prescnted on Fþre 2. The subsoils encountered, belÑ about one foot oftopsoil, consist of 3 to 4 feet ofsandy silty cþ overþing silty sandy gravel with cobbles. Results of swoll-consolidatioa testing performed on relativèly undisturbed samples of thc sandy siþ clay, presented on Figure 3, indicate low compressibility under existing moisture conditions and light loading. The samples were moilerateþ compressible r¡nder additional loading afrer wetting. Resr¡lts of à gradation analysis performed on a sample ofsitty sandy gravel with cobbles (minus I inctr ftactioni obtained from the site are presented on Figure 4. Free water was observed in the pits at qø +r/, feet deep at the time of excavation. The sdils above the water level were moist. Foundation Bearing Conditions: The upper clay soils have alow bearing capacityand Pm9 settlement potential. These soils are t¡pically known to be "ompressible-underloading whe,n wetted. The groundwater levei in the area is relatively rhullo* and other sources.ofwetting inclr¡de utility line leaks, drainage and lawn irrigation. The owner should be aware of the risk ofsettlement associated with foundations bearing on the clay soils. We recommend placing footings at about 2 feet below the existiug grourd surfaco to avoid construction below the water table and on the deeper vety moist to wet clay soils. An altsrnative would be to bear onthe underlying gravel soils but this would require dewatering during construction of the footings. The underþing gravel soils have a higher bearing capacity with a minor settlement poterrtial. Grounrclwater was encountered in the pits at the approximate claylgavelcontact. Another altemative would be to remove the clay down to the gravel and place struçtural fill such as compacted sceened rock or'þit run" gravel back up to desþ footing grade. Foundation Recommendations: Considering the subsoil conditions encountered in the e^xplgratory pits and the nature ofthe proposed oonstruction, \rye recornmend spread footings placed on the upper undisturbed natural clay soil within about 2 feet ôf tn" ground surface for support ofthe proposed residence. Spread footings bearing on the uppêr clay should be designed for an allowable soil bearing pressure of 1,200 psf Spread footings bearing on the underlying granular soil or structural fill can be designed for an allowable soil beariqg pressure of2,500 psf The upper soils tend to compress after -wettp8 and there could bq some post-construction foundation settlement. Footings bearing on clay soils should have a miuirrrrrm width of l8 inches for continuous rialls and 24 inche,s for columns. Footings bearing on granular soils should have a minimum width of 16 inches for continuous walls and24 inches for columns. 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 natural soils. Exterior footings should be provided with adequate cover above their bearing elevations for fiost protection. Placement of footings at least 36 inches below the exterior grade is typically used in this area. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming m unsupported length of at least lZ feet. Foundation walls aoting as retaining structures (if any) should be designed to resist a Job Nol 13 2234 Gåful -3- lateral.earth pressure based on an equivalent f{uid unit weight of at least 50 pcf for the on- site soil as backfi"ll. A representative ofthe geotechnioal engineer should obsen¡e all footing excavations prior to concrete placement to evaluate bearing conditions. Floor Slabs: The natural on-site soils, exclusive oftopsoil, are suitable to support lightly loaded slab-on-grade construction with some risk of settleÍrent should the subùils becomc wþtted. To reduce the effects of some díffereutial movement, floor slabs should be separated from ¿ll bearing walls and columns with expansion joints which allow unrestrained vertical movement. Floor slab conhol joints should be used to reduce damage due to sluinkage cracking. Therequirements for joint spacing and slab teiuforcement should be established by the designer based on experieñce and the intended slab use. A minimum 4 inch layer of free-draining gravel shoud be plaoed beneath basement level slabs to facilitate drainage. This material should consist of minus 2 ¡¡¡¡ch aggregate with less than 50% passing the No. 4 sieve and less than}o/opassing the No. 200 sieve. All fÏllmaterials for support of floor slabs should be compact'ed to at least 95% of maximum standatd Proctor density at a moisture content äear optirnum. Required fill can consist ofths on-site soils devoid ofvegetation, topsoil an¿ oversized rock. Underdrain System: For the proposed slab-on-grade constructior¡ we recommend that an underdrain sptem not be installed. Surface Dralnage: The following drainage precautions should be observed during construction and maintained at all times afrer the residencê has been completed:l) Inundation ofthe formdation excavations and underslab arãas should bç. avoided 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 sl¿b areæ and to at least 90% ofthemaximum standard Proctor density in landscape areas.3) The ground surface surrounding the exterior of the building should be sloped to drain away ûomthe foundation in all directions. we recommend a minimum slope of6 inches in the first l0 feet inunpaved arcas and a minimum slope of 3 inches in the first 10 feet in pavement and walkway areâs.4) Roof downspouts and drains should discharge well beyond the limits ofall backfill.5) Landscaping which requires regular heavy irrigation should be located at least 5 feet from the building Lirnitationsl This studyhas been conducted in accordance with generally accepted geotechnical engineering principlcs and practices in this area atthis time. We make no waranty either expr€ss or implied. The conclusions and recommendations submitted in this report are based upori the data obtained from the exploratory pits excavated at the locations indicated on Fþre I and to the depths shown on Figure Z,theproposed tlpe of construction, and ow experience in the area. Our services do not include deteffiining the Job No.l 13 223Â eeFtecrr -4- pl'esellce, prevention or possibility of nrolcl or either biological contalninants (MOBC) cleveloping in the future. If'the client is concernecl about MOBC, tliep a profèssional in this special frelcl of practice shoulcl bc consultecl. Our finclings include interpolation ancl extrâpolâtion of the subsurtàce conditions iclentitied at the exploratory pits and variations h the subsurfÌrce corrditions nray not lreconre eviclent until excavation is perfurmecl. tf conditions eltcoulttetecl cluring construction appear clifferent ÍÌom those clescribed in this repoft, we shotllcl be riotifiecl at once so re-evaluation of the recommendations may be rnacle. This report has been prepared fi¡r the exclusive use by our client tbr clesign purposes. We are not responsible fbr technical interpretatieins by ofhers of our ilrlòrmation, As the project evolves, we should provicle continued consultation ancl field seruices cluring cr¡nstructiotr to review and monitol the irnplementation of our rccolnnteu(lations, ancl to verifu that the recorntnendations havc been ap¡rropriately interpretecl. Significant clesign changes may require additional analysis or modifìcations to the recor¡menclations prescnted herein. We recommencl on-site observation of excavations and foundation bearing strata and testing of structural fill by a representative ofthe geoteclurical engrneer. If you have any questions or if we may be of further assistance, please let us know Respectfu lly Submitted, HËPW G CHNICAL, INC Louis Eller Revicwed by: Danicl Flardin, P l,,EE/ksw attachments Figure 1 *loratory Pits Figure 2 - Logs of Exploratory Pits Figure 3 * Swell-Consoliclatian Test Results Figure 4 - Claclation Test Results 'l'able I - Sulnmary of Laboratory Testing Job No. I lJ 2!.iA c;,&Çtecr' APPROXIMATE SCALE 1" = 30t EQUESTRIAN WAY PIT 1 I LOT E4 LOT E2PIT 2 I LOT E3 L J 113 2234 LOCATION OF EXPLORATOHY PITS Figure 1 PlT 1 PIT 2 0 0 h H 1TFo- UJo WC=15.3 DD-106 WC=I5.6 DD-104 *4=84 h TUIL trÞ o_t¡ô 5 -200=16 b 10 10 ,L.E.GEND: n n ffi þ l.: TOPSOIL; organic sandy silt and clay, roots, seft, moist, dark bror¡¡n. CLAY (CL): silty, sandy, stiff/molst to sofUræry moist with depth, brown, GRAVEL (GP-GM); cobbfes, small boulders, sandy, slightly silty, wet, medium densê, brown, Rêlatively undisturbed Zlnoh diameter linor sample. Disturbed bulk sample, Free water level in plt at time of excavating. NoïES: 1. Exploratory plts were excavated on July 3, 2013 with a John Deere mini-excavalor, 2. Locatlons of exploratory pits were measured approximately by paclng from featurss shown on the site plan provided. 3. Elevatlons of exploratory pils were not measured and the logs of exploratory pits are drau¡n to dopth. 4. The exploratory pit locations and elevatfons should be consldered accurale only to the degree implied by the method used. 5, The lines between materials shown on the oploratory pit logs represent the approximate boundaries betwe€n materialtypes and transitions may be gradual. 6' Water level readings shown on the,logs were made at the time and under the conditions indioated. Fluch.ntions in water level may occurwith time. 7. LaboratoryTesting Results; WC = WaterContent(0,6) DD - Dry Densiry ( pcf )+4 = Percent retalned on the No. 4 s¡eve -200 = Percent passing No.200 sieve 1132234 LOGS OF ËXPLORATORY PITS Figure 2 percent pcf Moisture Content = 15.9 Dry Density = 106 Sample of: Sandy Silty Clay From: Boring 1 at 2 Feet t \ I I I \I I \t - No movement upon wetÜng 0.1 1.0 f0 f00 10 APPLIED PRESSURE (t<sf ) APPLIED PRESSURE ( ksf ) 0 \oat\ zoı ßEo.Eoo 2 1 I 4 5 0 I \oo\ 7Iv, CN UJÉ,o.Eoo 2 3 4 5 percont pcf Moisture Content = i5.6 Dry Dansity = 104 Samplo of: Sandy Silty Clay From: Boring 2 at 2 1 12 Feat \ I I I I I No movement/ upnwetting \ \ \ I , 1001.00.1 fi1n1A SWELI-.CONSOLIDATION TEST RESULTS Fígure 3 !aH[. tHR ,rt Mll, tå M¡rt ïlrE READ¡NOS to¡llt lgilbr tMN.It¡t{. ,fr tt00 u.s, Sf NDARD SERIÊS rfto ,30 .r0 a¡i1 gr CLEAR SQUAREOPËNT{Gs c¡l¡lz El¡,t E t¡JoîEl¡¡È 30 ¡10 50 ozU'U, o. 2u¡oEuo- 'æl 'æ 'dı 't ¡10 ¡l' 'slf iio 'so '600 r.to eN 1:rt cô f¿"6 t9¡ t¡,Ç rs' 'errrc 2ß DIAMETER OF PARTICLES IN MITUMËTERS ct-AYTOStLl Gravel 64 %Sand 20 lo Sllt and Clay 16 "Á Liguid Umit oÂ Plasticity lndex % Sample of:.silty sandy Gravelwith cobbles Fromr Boring I at 4 Feet to 5 Feet OA¡þ on vÊ, aNe uEDrÀr I co¡nst FIIE COAft¡É 1132234 GtÌhor¡rÌ GRADATION TEST RESULTS Figuro 4 HEPIÍT|ORTH-PAWLAK GEOTECHNICAL INC.TABLE 1SUMMARY OF I.ABORATORY TEST RESULTSJob I'lo. 113 2æASOIL ORBÐROO(TYPESardy Silty CIaySandy Silty ClayUì¡CONFIT{EDær{PR6SnESIR TíTH(PSF}P¡¡SrICINDÞ((o/ì\UQUIDllûrrrPERCBITPASSNGNO.200STA'E16GFAD¡T¡ONSA¡ID(96)?fiGRAIGL(96)&NATURALDRYDE{SITY(Dcf)106104NAruRALMO¡sTUREONIE¡T(%)15.3rs.6Dtrn:lffrt24ûo52u2PTTI2