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Home My WebLink AboutSubsoil Study for Foundation Design 06.30.2014iã ã F f/G Ë"f ç'.1 * F¡å'ÉJ{-¡\ E *ä*TEÇ'4i-jtf.qL Ì-år:ari!:1 rr'r!ìni:!iìt\.i.,1. (,ìt, il::¿:J::r!i¡ì+ l;r:..t ..'t,,''¡¡¡. !l .ì !i¡ {;1, ,.,. ...j -,1,ir,: . I ,1,.i.,i.. ,;i,.'l 1ìl¡r:t'r.:: fi ?lt"íl.l.i i! ¡r;i¿¡ l:::. : ;]r:'"': :t:; :i*¡tr lt . r. ,,1 r': -', , ,rlrl., , '1 ::ì.L..:rì STTBSOIT, STUDY r,OR }'ÛUNDATTON DESIGN PROPOSED ADDTTON TO EXISTI¡{{} HOT]SE AND RV STORAGE/GREENHOUSE STRUCTURE 2621 COUNTY ROAD lOO caRËCItìrDALE, COLORADO 81623 JO.B NO, tt4 ?3üA JUNE 30,2û14 P.REPAREÞ FIOR: LARRY & LISA SINGER 262I COTINTY ROAD lOO CARBONDALI, COLORADO 8l 623 f,**¡ gel #:qç¡TcPår'r¡q{ ,M l-;,r¡,1,c¿- -iil'l-$4¡-î'lj,ij * {,..;i+r'i.rr:ìt, S¡ri¡1.¡¡ ?lll-ti.lì.ii¿i: + ¡ii.r-,,,¡"rJi¡rr¡1* !?iÌ-4i!;i-llirqll TÄBLE OF CONTENTTS PURPOSE AND SCOPE oF sTUDy.... ....._..........._ r _ PROPOSED CONSTRUCTION...... .......- 1 - SITE CONDITIONS .,.,,",...,,-2 - FIELD EXPLORATION .....- 2 - SUBSURFACE CONDITIONS..... ,.,.....3 . FOUNDATION BEARING CONDITIONS............... ....,.........- 3 - DESIGN RECOMMENDATIONS. ........- 4 -FOLrNDATI0NS......... ..._ 4, FLOOR SLABS .......,.......- 5 _ UNDERDRAIN SYSTEM ................r 5. SIIRFACE DRAINAGE .............,...,.r 6 - LIMITATICINS ......... FIGURE 1 - LOCATION OF E}ßLORATORY BORINGS FIGURE 2. LOGS OF EXPTORATORY BORINGS FIGURE 3 . LEGEND AND NOTES FIGURË 5 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS PUR}OSE. AND SCOPE Or' STUI}Y This report presents the results of a subsoil sfudy for proposed additions to the current residence and a new RV Storage/Greenhouse Stucture located at 2621 County Road 100, east of Carbondalq Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recomme,ndations for tho foundation desþ. The study was conducted in accordance with our proposal for geotechnical engineering services to you' dated June 9,2014. A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of fhe subsoils obtained during the field exploration were tested in the laboratory to determine their classification and other engineering characteristics. The results of the field exploration and laboratorytesting were anal¡zed to develop recommendations for foundation t)pes, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conslusions, design recomrnendations and other geotochnical engineering considerations based on theproposed construction and the subsurface conditions encountered. PROPOSED CONSTRT¡CTION The proposad addition to the existing residence is an attached two story addition on ths east side of the residence and the RV Storage and Greenhouse Structure will be located southwest of the existing residence. The attached addition to the house will have a slab- on-grade or a strucfural floor over a crawlspace and be of similar consfuction to the existing residence. Ground floors for the RV Storage and Greenhouse Structurewill be slab-on-grade. Grading for the additions is assumed to be relatively minor witl cut depths between about 2 to 4 feet. 'We assume relatively light foundation loadings,'typical of the proposed tlpe of construction. JobNo. ll4230A eåFtecr'r -2- Ifbuilding loadings, location or gradingplans change significantly from those describçd abovg we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITTONS The site is currently occupied with a single family residence located in the middle of the lot. The lot is bounded to the north by the Roaring Fork River, to the south by County Road 100 and to the east and west by adjacent residential lots. A small outbuilding is located northeast of the residence and adjacent to the Roaring Fork River. The lot is relatively flat with a sligtit slope down to the north. Shallow inigation trenches cross the southwest portion of the site, Vegetation on the lot consists of grasses, shrubs and mature hees. F'IELD EXPLORATION The.field exploration for the project was conducted on June 19,2074. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 4 inch diameter continuous flight augers powered by a tgck-mounted cME-458 drilt rig. Tho borings were logged by a representative of Hepworth-Pawlak Geotechnical, Inc. Samples of the subsoils were taken with a l% inch spoon sampler. The sampler was driven into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This test is similar to the standard penetration test descríbed by ASTM Method D-1586, The penetration resistance values are an indication of the relative density of the subsoils. Depths at whioh the samples were taken and the penefuation resistance values are shown on the Logs of Exploratory Borings, Figure 2. The samples were reh¡rned to our laboratory for review by the project engineer and testing. Job No. 114230A c;å&ecrr -3- SUBS TIRF'A,CE COIYDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about 4 to 6 inches of topsoil overlying silty sandy gravel with cobbles and boulders. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilting reft¡sal was encountered in the deposit. Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of gradation analyses performed on small diameter drive sarnples (minus lYz înckfraction) of the coarse granular subsoils are shown on Figure 4. The laboratory testing is summarized in Tabre l. Free wat€r was encountered in Boring 1 at 7 feet at the time of drilling and at 4% feet when checked 12 days later. Boring 2 caved at shallow depth during augor removal and a water levei check was not possible. The 5 foot sample from Boring 2 was wet. Subsoils above the water table were slightly moist to moist. T,OUNDATION BEARING CONDITIONS Foundations bearing on the natuml granular soils encountered in our exploration should be feasible for support of the proposed struòture with some risk of movement. All topsoil, any fill, and all loose or disturbed materials should be removed from the building area and the foundation excavations extended down the natural relatively dense granular soils. Groundwater was encountered in our exploration at relatively shallow depth and may impact foundation construction and dewatering of foundation or utility trench excavations may be necessary. Job No. ll4?l'AA eåFtecn -4- DESIGN RECO}Í MENDATIONS FOI,INDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommerrd the building additions and RV StoragelGreenhouse Structurebe founded with spread footiñg.s bearing on the natural granular soils. The desigu and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural granular soils should be designed for an allowable bearing pressure of 2,500 psf. Based on expetience, we expect settlement of footings designed and conskucted as discussed in thís section will be about 1 inch <ir less. 2) The footings should have a minimum width of 16 inches for continuous \ryalls and 2 feetfor isolated pads. 3) Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing eievation for frostprotection. Placement of foundations at least 36 ínches below exterior grade is fypicallyused in this area. 4) Continuous foundatíon walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 10 feet. Foundation walls acting as retaining structures should also be designed to resist a lateral earth pressure. 5) Any existing fili, topsoil and pny loose or disturbed soils should be removed and the footing bearing level extended down to the relatively dense natural granular soils. The exposed soils in footing area should then be moistened if needed and ðompacted. If water seepage is encountered, the footing areas should be dewatered before concrete placernent. Job No. 1t4230Ér eå$tecn -5- A representative of the geotechnical engineer should observe atl footing excavations prior to concrete placement to evaluate bearing conditions. FLOOR SLABS The natural on-site soils, exclusive of topsoil arc suitable to support lightly loaded slab- on-grade construction. To reduce the effects of some differential movemen! floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestained verfical movement. Floor slab control joints should be used to reduce damage due to shrinkage cracking, The requirements for joint spacing and, slab reinforcement should be established by the designer based on experience and the intended slab use. All fill materials for support of floor slabs should be compacted to at least 95% of maximu¡n standard Proctor density at a moisture content near optimum. Required fill can consist of ths on-site granular soils devoid of vegetation, topsoil and oversized rock. LTNDERDRAIN SYSTEM Free water was encountered during our exploration and wilt likely fluctuate with river levels, heavyprecþtation and seasonal runoff. Frozeu ground during spring runoffcan also create perched conditions. We recommend below-grade construcfion, such as retaining walls and crawlspace a^reas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. If a crawlspace is constructed for the addition, shallow seasonal groundwater rnay impact the crawlspace area and a sump with an adequate pump may be nccessary. Slab-on-grade construction should not require an underdrain system. If installed, the drains should consist of drainpipe placed in the bottom of the wall backfill surroundsd above ihe invert level with free-drainíng gtanular 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 lYo grade to a sump and pump. Free-draining granular 6) Job No, ll4230{cåBtecrr -6- material used in the underdrain system should contain less'than 2% passing the No. 200 sievq less than 50% passing the No, 4 sieve and have a maximum sizeof Zinches. The drain gravel bac,kfill should be at least llle feet deep. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maiatained at all times after the additions have been completed: 1) Inundation ofthefoundation excavations andunderslab areas shouldbe avoided during conshuction. 2) Exteriorbackfill should be adjusted to near opimum moisture and compacted to at least 95o/o of themaximum standard Proctor density in pavernent and siab areas and to at least 90% of themaximum standard Proctor density in landscape areas. 3) The ground surface surrounding the exterior of thebuilding should be sloped to drain away from the foundation in all directions. \Ve recommend a minimum slope of 6 inches in the first l0 feet inuupaved areas and a minirrnrm slope of 3 inches in the first 10 feet in paved areas 4) Roof downspouts and drains should discharge weil beyond the limits of all backfill and foundation areas. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering princþles and practices in this area at this time. S[e make no waranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratbry borings drilled at the locations indicated on Figure 1, theproposed type of construction and our experience in thè area. Our services do not include determining the presence, prevention orpossibility of mold or other biologieal contaminants (MOBC) developing in the fi¡ture. If the client is concerned about MOBC, then a professional in this special field of practice should be JobNo. ll4230A eåFtecrr -7 - consultecl' tur finelings includs interpolation and extrap*lation of the subsurf¿ce conclitions identified at the exploratory barings and variations in the subsurfuce conditions ma¡r not become evide¡t ultil excavatisn is perfonnerJ. If conditions cncountered during construction appeat different froru those described in this rêport, we should be notified so thaf re-çvaluation of the recomme{dations may be made. This report has been prepared for the çxclusive use by our client for design purposes. Vfe arç not respnnsi-n'le for technieal intelpretations by otliers of our infomration. As the project evolves, we should provide continued consultation and field services'during construction to review and monitor the implementation of aur recommendations, ancl tc verify thåt thç recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommenclatir:ns presented herein, We recommend cn.sitc observation of excavations and tbundation boaring strata and testing of structural fiIl by a representative sf lhe geotechnical engineer. Respeetfully Submitted, HEPWORTH - PAWLAK James A. Parker, P.8., P.G. Reviewed by: C. Daniel Ë. Harclin, P,Ë, JAP/ ksw cç:J eff D i ckenson .- -b.i qiçi:rt {q!* îi$f -rårL*J Job No. l,l4 ?304 Ætecrr I I 1 ) f"" "' o ts !, \ I I I \ I I r I I I- .1. f \ s åc¡rss,\ ',, I t I I I 1. ?014 G FOHK R'h,. -br ed'x?t :4';".hb l)d ¡I4¡ ¡r l7 /r- I I I Ials4-'' /a ûÉ öÉ .143 ì 1'{nË) SEPIIC.t TANK,LTþs\G) 'ü .:- 6"ôPF---*]üf;E-efîìã ( I I ¡/*r f¡gr ***t-"'' ,JNY,i2g,l,7tì.{ :l: ^ t. rgf;,f ql 4 Juy+rq.se*f 4p L¿I i \,/"^62âã-y' !4þ ç- ::*\ -s'¿, .' - '-.,¡' .j'' I 114 g3ûA ¡fi;\5q t-lFFwe]51"t"¡-t.I l LûCATIûN TF ËXPLORATORY BOR¡NGS TfiCHf{}Cê.,. FIGURË 1 EüRING 1 ELËV.* 6254' BOffINÊ å ËLEV.:6ã56: 6260 þZOU 6?55 6?55 0)tl LL Ic0 {û (t)ü 4U12 0)(},tL ! o'Ãl (ÌJ (¡) m 4tÍ12 WC=4.0 *,4=51 -200*8 21112 WC-8.3 +4*55 -20û*9 29/1 2 6?5CI 6250 6â45 6?45 Note: Fxplanätion of symbol$ is shown on Figure 3" 1'r4 23tA Æecl,: Uf *ìrffig.üÀk! itr' CF^f ¡u*{ÊÃ¡ LüG$ OF ËXFITRATÜËY BON¡NGS FIGUNË 2 W LËGËND: TOPSû|L; silty sand with gravel, rsotst slightty moist, brown. GÊAVEL (GM); silty, sancJy, with cobbles and boulcJers, mediurn dense to dense, moist to wet, brown. I I Drive sample; standarsl penetration test (SPQ, 1 3/B inclr l,D. splít spoÕn sample, ASîM E"]SB6, I ^a t1,., Drive sa.nrple blow count; irrdicates that 48 biolvs of a 140 pound hammer falling 30 inches werelot t¿ required to drivethe SPT sampler 12 inches, ry Free water level in boring and days after drilling meâsurement wâs tãken. --*-? Depth at which boring had caved when measured after dri{ling, tf Practicaldrillingrefusal, I NOTES: 1, Exploratory borings were dritled on June 19, 2014 wiih 4-inch diameter contínuous flight porruer augôr. 2. Lr¡cations of exploratory borings were measured approximåtely by paeing from features shown on the site plan provided. 3. Elevations of exploratory borings were obtained by lnterpolation between contours shown on the,sitö plan provided and checked by instrument level, 4. The exploratory boring loeations and elevations should be considered aecurate only to the degree implied by the method usecl. 5. The lines between materials shown tn the exploratory boring logs represent the approximate boundaries between material types and transitions rnay be gradual. 6. Wâter level reaciings shown on the logs were macle at lhe t¡me and under the conditions indicated Flucluations in water level may occur wiTh time 7. Laboratory Testing Resufts: WC * Water Content (%} *4 : Percent retained on the No. 4 sreve -2t0 : Fercent passing No.200 sieve 1 14 23ûA turroðñT*.*¿*r ¡d *f,ñJr¡&Àt¡¡i $-"4Ë {3eNbtechr LËüËND AND f{üTËS FIGUËE 3 LJI¡ IÜL 7 SIANÐARD S€FIES ,4 .001 .W .0t5 :00! irs .Õ3? ,Ò7i! .liû .$ô .6ù ì.t8 2.36 OIAMETEF OF PARTICLES IN MILLIMETERS 6 #8 #4 3/8', 314' 1112 3r ð6n 8r 1üJ: !0 C'^zu}U) ruß- f,.:"^z Q.^ü u :!0 t{) ro 10 ä0 .JU 40 60 7t 80 90 1û0 .ô LU¿ Fñü t---ztu c lÅl o- 4J5 76.2 f5â 2ô.3 l¿1 18,ût?.5 ''.'"..._ .- * * GRAVËL 51 To LIQUID LIMIT YO SAMPLË OF; Slightly $itry Sandy Gravet .00r ,002 SAND 41 % SILT AND CLAY 8 '/O PLASTICITY INDEX EÃ FROM: Boring 1at Z Feer crÊÁR OFENING$znR 15 MIN;4 MtN. 1 .tt6.û09 .û19 .097 ,024 .15û .00ß .S00 1.18 2.36 4.78 DIAMETËR OF PARTICLES IN MILUMETERS u.s, 80 7a1û {J)uos þaoZ-. LU C)40ffi Õ- 30 *80045 0 10 â20 Lt¡Z3ü Ftlj án G þ-z. 50 IJJOE60 Lü r'\ 70 st4^ t 112^ 3' 5'6. 8- 100 80 et tû 0 åt 100 s.q2.51e.û 37,6 76â lrlË ?03 titEVL A[{AL L # F t. + .t--{ .t- | - -Í r- -.r --.¡ ¡ CI.AY Td} .ìLT GA,A.VFL 55 "/U LIEUID LIMIT SAMPLË CIF: Sl SAND 36 % PL.ASTICITY INDËX tsStJLÈs SILT ANil üLAY 9 YO a//ô 2 at 2 and 5 Feet /o FRCIM: 114?3tA ilf MÂÛT!.*^*t if lf, ff sÈ*Èri,"!Èi GAADAT¡ÜN TË$T NISULTS FIGURË 4 HEPWORTH-PAI'ULAK G EOTECHNICAL INC.TABLE 1SUIIIIMARY OF LABORATORY TEST RESULTSJob No,1142tAASOILTYPEStightly Silty Sandy GravelSlightly Silry Sandy GravelUNCONFfNEDCOIHPRESSIVESTRENGTH{PSF)PLASNGINDEXt%lUQTJIDUM¡Tl1ú;tlIPERCENTPASSINGNO.200SIEVEISAüID(%ì514136GRAVEL{%}55I{ATURÀLDRYDENSITYfÞcf)I.¡ATURALMO]STURECONTENTtTol4.08.3.ocATtoNBORINGDEFTH22&s1')