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Home My WebLink AboutSubsoil Study for Foundation Design 03.29.2023rcn fiumas & S*sorlatesu lnu," Ge*i*chni*al and Maieiiais f;rigineeia 502{l County lioacl 154 and fnvirannenlal $dentists Clcn.,vooii Sprin-ss, CO 81601 phone: 1970J 9+5-798S firx: (970) 945-8454 etnail : kaglcnrvood(g)krnnanrsa.cour An fmp{oye* Qrtcned figsap#&y rvvu-la,-k}r'arusa.{i]ltl SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE NORTHEAST OF CARBONDALE "TBD HIGHWAY 82 ACROSS FROM *PLANTED EARTH'' GARFIELD COUNTY, COLORADO PROJECT N(). 23-7-189 MARCH 29,2023 PREPARED FOR RAM DEVELOPMENT ATTN; BOBBY AI,MAZAN P.O. BOX r387 CARBONDALE, COLORADO 81623 fu q*3fu y (ri : r xwz rk:v,fu ry E* <1 TABLB OF CONTBNTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS FIELD EXPLORATION SUBSURFACE CONDITIONS DESIGN RECOMMENDATIONS .................... FOI-TNDATIONS FOUNDATION AND RETAINING WALLS FLOOR SLABS LTNDERDRAIN SYSTEM .. ......... SITE GRADING........... SURFACE DRATNAGE.............,., LIMITATIONS FIGURE I - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS FIGURE 5 GRADATION TEST RESULTS TARLE I. SUMMARY OF LABORATORY TEST RESUT,TS 1 a-L 3 J J 4 5 5 6 6- Kumar & Associates, [nc. o Pr*ject No. ?3-7-1Sg PURPOSE AND SCOPE OF STUDY This report presettts the results of'a subsoil study lor aproposed residence to be located along Higliway 82 trortheast of Carbondale arrd across from "Planted Earth", Garfield County, Colorado. The project site is shown on Figure l. The puryrose of the study r.vas to develop recommendations for the foundation design. The study rvas conducted in accordance with our agreenrent for geotechnical engineering senrices to Rarn Developmerrt dated March l5,2023. A fie ld exploration program oonsisting of exploratory borings was conducted to obtain information on the subsurface conditions. Sarnples of the subsoils obtained during the field exploration were tested irr the laboratory to determine theil classification, colrpressibility and other engineering charactedstics. The results of the field exploration and laboratory testing were analyzetl to clevelop recomrrendations fbr fbundation types, depths and allowable pressures for the proposed building for.mdation. This reporl summarizes tlie data obtained durirrg this study and presents our conclusions, design recommetrdations and otlier geotechnical engineering considerations bascd on the proposed construction and tlrc sLrbsurface conditions encountered. PROPOSED CONSTRUCTION We assume that the proposed residence r.vill be a tr,vo story structure located above the steep slope down to tlre Roaring Fork River in the sor,rthwest part ol- the lot as shown or-i Figure I . Ground floor could be structural ovcr crawlspace or slab-on-graclc. Grading for the structure is assumed to be relatively minor with cut depths betrveen about 3 to 6 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significarrtly frorn those described above, we should be notifiecl to re-evaluate the recomntendations contained in this report. SIl-E CONDITIONS The building area is located on a topographic bench between the south-facrng stccp cmbankment slope belorv Highway 82 to the ttotlh attd the 2O-fbot very steep slope down to the Roaring Fork Riverwhich encompasses the southern half of the property. The building area will be located in the eastern part of the lot between 1he 50 foot Highway 82 setback and the 35 foot setback from the high water line of the Roaring Forl< River. We understand that the or,vner may apply for a variance to reduce the 50-foot highway setback. The flatter part of the site, where the house will be located, slopes gently down to the south and is vegetated r,vith scattered trees and sage brush with grass and rvceds. No evidence of slope instability, such as ground cracks and slulps, was observed in the assunted building area. Tlte bedrock exposed in the steep drop off down to the river is composed of red sandstone/siltstone of tlre Maroon Fonrration. Kunrar & Assoeiates, lnc. 0 Project No. 13,7"189 1 FIET,D BXPI,ORATION The field exploration for the project was conducted on March 16,2023. Tr,vo exploratory borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions. The borings were advanced with 4-inch diameter continuous flight augers powered by a truck- mounted CME-458 drill rig. The borings were logged by a representative of Kumar & Associates, Inc. Samples of the subsoils were talcen with l3Ainch and 2-inch I.D. spoon samplers. The samplers were driven into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This test is sinrilar to the standard penetration test described by ASTM Method D- 1586. The penetration resistance values are an indication of the relative density or consistency of the subsoils. Depths at which the sarnples were taken and tl-re penetration lesistance values are shorvn on the Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the ploject engineer and testirig. SUBSURFACE CONDTTIONS Graphic logs ol-the subsurl'ace conditions encountered at the site are shown on Figure 2. The subsoils consist of abor-rt I foot of topsoil overlying2lo 4t/zfeer of stif,f, sarrdy silt and clay overlying relative ly dense, slightly silty sandy gravel and cobbles. Drilling in the dense granular soils with auger equipmenl was difficr-rlt due to the cobbles ancl possible boulders and drilling refusal was encounterecl in the deposit in both borings at 9 feet. The gravel and cobble soils are underlain by beclrock rvhich the borings may have refused in but additional subsurface exploration such as with a large trackhoe is needed to develop this information. Laboratory testirrg performed on sarnples obtained from the borings included natural moisture content and density and gradation analyses. Results of swell-consolidalion testing performed on a relatively undisturbed drivc samplc of thc silt arrd clay soils, presented on Figure 4, indicate low compressibility under light loading and a high collapse potential (settlement under constant load) when wetted. Results of gradation analyses perfonned on a small dian-reter drive sample (ririnus lYz-incl't fraction) of the coarse granular subsoils are shor,vn on Figure 5. The laboratory testing is summarized in Table l. No fi'ee water was encountered in tlie borings at the tirne of drilling and the subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS The derse gravel soils encountered at 3 to 5'/zfeet deep are suitable for sr-rpport of the proposed residence. The topsoil and sandy silt and clay soils should be removed fi'om below footing areas Kumar & Ass*eiates, ine. G Project l{a. *3-7"189 J and the bealing level should be extencled down to tlre underlying dense gravel soils. The footings should be set back around I 0 feet fronr the top of the very steep down slope to not adversely impact the slope stability. DESIGN RECOMMENDATIONS FOUNDATIONS Corrsidering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, lve recomnrend the building be founded with spread footings bearing on the natural granular soils. The design ancl constmction criteria presented belorv should be observed for a spread footirig foundation system. l) Fclotings placed on the r-rndisturbed natural granular soils should be designed for arr allowable bearing pressure of 3,000 psf. Based on experience, we expect settlement ol- Ibotings clesigned and constructed as discussed in this section will bc about I irich or lcss. 2) The footings should have a minimunr width of I6 inches lor continuous walls and 2 feet for isolated pads. 3) Exterior footir,gs and l'ootings beneath unheated areas should be provided with aclecpate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this area. 4) Clor-rtinuous fourdation walls should bc rcinfbr-ced top and bottom to span local anomalies such as by assuming an unsupported length of at least I0 feet, Foundation walls acting as retaittittg structlrres should also be designed to resist lateral earth pressures as discussed in the "Foundatiou and Retaining Wzrlls" sec;tion of this report. 5) The topsoil, clay soils and any 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 fcroting area should then be moistened and cornpacted. (',) A representative of the geotechnical engineer should observe all fbotirrg excavations prior to concrete placement to evalnate bearing conditions. FOUNDATION AND RETAINING WAL,LS Foundation walls ar,d retaining structures wliich are laterally supported ancl can be expected to undcrgo only a slight arr-rount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 50 pcf for backfill consisting Kumar & Ansoeiates, lnc. @ Project No.23-7-189 -4- of the on-site soils. Carrtilevered retairring stluctures ivhich are separate fronr the residence and can be expected to deflect sufficiently to mobilize the full active earth pressure coriditiorr should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 40 pcl'for backfill consisting of the on-site soils. All foundation and retaining stluctures should be designed for appropriate hydrostatic and surcharge pressures suclr as adjacerrt footings, traffic, constructiou materials and equipment. The pressures recommended above assulne drained conditions behind the walls and a horizontal backfill surface. Thc buildup of water behind a wall or zln upward sloping backfill surface will inclease the lateral pressLlre imposed on a fbundation wall or retaining structure. Au underdrain should be provided to prevent hydlostatic pressure buildup behind walls. Backfill should be placed in unifbrrn lilts and compacted to at least 90oto of the maximunr standard Proctor density at a moisture contenl near optinrunr. Backfill in pavement and walkr,vay areas slrould be compacted to at leasl95%o of the maxirnum standard Proctor density. Care sirould be taken not to overcolnpact the backfill or use large equipment near the wall, since this could cause excessive lateralpressure on the wall. Sorne settlement of deep foundation wall backfill should be expected, even il'the material is placed correctly, and could result in distress to facilitics constnrcted on the backfill. Backfill shor.rlcl not contain organics, debris or rock larger than about 6 inches. The lateral resistance ol'foLrnclatiotr or retaining r,vall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the sicle of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of lriction of 0"50. Passive pressure of compacted backfill against the sides of the footings carr be calculated using an equivalent fluid unit weight of 350 pcf. The coefficient of friction and passive pressure values recommended above assunle ultimate soil strength. Suitable lactors ol-sal-ety should be included in the design 1o limit the strain which will occur at the ultimate strength, particLrlarly in the case of pttssive resistance. Fill placed against the sides oFthe footings to resist lateral loads slior"rld compacted to at least 95% of the maximum standard Proctor density at a moisture content near optirnunr. FLOOR SLABS The natural on-site soils, exclusive oltopsoil, are suitable to support lightly loaded slab-on-grade construction. To reduce the el'l'ects olsome dilfurential movement, floor slabs should be separatcd l'rom all bearing walls ancl colurnns with expansion joints which allow unrestraincd vertical movement. Floor slab cotttroljoints slioulcl be used to reduce damage due to shrinkage craclcing. The requirements for joint spacirrg and slab reinforcement should be established by the Ku*rar & Asscciates, lnc. 6)Project Na. 23-7-189 -5- designet based on experience and the intended slab use. A nrininrunr 4 inch layer of fi'ee- drainirrg gravel should be placed beneath basernent level slabs (if any) to facilitate drainage. This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve ernd less than 2%u passing the No. 200 sieve. All fill materials fclr suppotl of floor slabs should be compacted to at least 95% of maximum standard Proctor density at a moistur"e content near optimum. Required fill can consist of the on-site soils devoid o1'vegetatron, topsoil and oversized roclc. UNDERDRAIN SYSTEM Although free water was not etrcoutttered during our exploration, it has been our experience in the area that localperched groundwater can develop duririg times of lreavy precipitation or seasonal mnoff. Frozen grouncl cluring spring runoff can create a perched condition. We recommend below-grade construction, such as retaining walls, crar,vlspace and basement areas, be protected fiorn wetting and hydrostatic pressure buildup by an underdrain systent. The drains should consist of drainpipe placed in the bottom of tlre wall backfill surrounded above the invert level with liee-draining granular niaterial. The drain should be placed at each level of excavatiott and at least I foot below lowest adjacent finish grade and sloped at a minimum 1o/oto a suitable gravity outlet. Free-drainirtg granular naterial used in the underdrain system should cotrtain less tlran 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximunr size of 2 inches. The drain gravel backfill should be at least l% feet deep. SITE GRADING The risl< of construction-induced slope instability at the site appears low provided the building is locatecl abovc thc stcep slopc as planned, outside the 35-lbot river sctback and cut and fill depths are limited. We assume 1he cr"rt depths for the basement level (if any) will not exceed one level, about l0 to l2 I'eet. Fills should be limited to about 5 feet cleep, especially at the downhill side of the residettce where the slope steepetrs. Etlbanknrent fills should be compacted to at least 95% of the maximum stanclard Proctor density near optinrtinr moisture content. Prior to fill placement, the subgrade should be carefr-rlly prepared by removing all vegetation and topsoil and compacting to at least 95% of the rnaxirnum standard Proctor density. The fill should be benched irito the poftiotts of the hillside exceecling 20o/o grade. Permanent unretained cut and fill slopes should be graded at2horizontal to I vertical or flatter and protected against erosion by revegetation or other means. This of fice should revieu, site grading plans for the project prior to construction. Kunrar & Associates, lnc.'c Praject No. 23"7-189 -6- SURFACE DRAINAGE The following drainage precautiotrs should be observed during construction and maintained at all times after the residence has been completed: l) Inundation ofthe foundation excavations and underslab areas should be avoided dr"rring construction. 2) Exterior backfill shoLrld be adjusted to near optimum moisture and compacted to at least 95u/o ot'the maximurn standard Proctor density in pavement and slab areas and to at lcast 90% of the maxinrurn standard Proctor density in landscape areas. 3) The ground surface suruounding the exterior of the building should be sloped to drain away frorn the foundation in all directions. We recommend a minimum slope of 6 inches in the first | 0 fcet in unpaved areas and a minimum slope of 3 inches in tire first l0 ltet in paved areas. Free-drainir,g wall backfill should be covered with frlter fabric and capped with about 2 feet of the on-site soils to reduce surface water infiltration. 4) Roof dolvnspouts and drains sliould dischargc rvell beyorrd the lirnits of all backfill. LIMITA'TIONS This stLrdy 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 irnplied. The conclusions and recornmendations submitted in this report are based upon the data obtained from the exploratory borings drilled at thc locations indicatcd on Figure l, the proposed type of construction and our expetience in the area. Our services do not iuclude detemrining the presence, prevention or possibility of niold or other biological contaminants (MORC) developing in the ['uture. If tlre client is concerned about MO[]C, then aprof'essiorral in this specialfield of practice should be oonsulted. Our findings include interpolation and extrapolation of the subsurface conditions identified at the exploratory borings and variations in the subsurface conditions may not becolne evideut until excavatiori is performed. If conditions encountered durirrg construction appeal different from those described in this repofi, r,ve should be notified so that re-evaluation of the recommendations may be made. This report has been prcparcd for the exclusive use by our client for design pulposes. We are not responsible lor technical interpretations by others of our information. As the project evolves, we shoulcl provide continued consultation and field services durirrg construction to review and monitor the implementation olour recornmendations, and to verify that the recommendations have been appropriately interpreted. Significant clesign changes may require additional analysis Kum;lr & Assoe iaies, lnc. o)Pr*ject No. ?3"7.189 -7 - or modificatiorrs to the recommendations presented herein. We recommend on-site observation of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Subrnitted, Kzemzzr & A*sscing**^ Eaz*, Daniel E. Hardin, P.E Reviewed by: Steven L. Pawlak, P.E. DEH/kac Kumar & Associates, lnc. s Project No. 23.7.189 !.lllYit {g tp-Rt4.t{X'f.tiri{ - ^, . -..i)1-tlt!*sl?.'Er.fj'ret\il} Atlj?riilt|t . , 7w/riaYg?:&.t${iu- .- . trHat{4 M L t tittzlt., ft*t:?t o BORING 2 i - . 1ft ,*1r3l: 1!1!t;tt A!:'6 | i:P,ga&v|rt*{n}\!ril! t P,nT'B{'{. BORING 1 ' ftt6;t -9, Y #!--* -"',*.*-*,* vs''ilj.:i-, ttdrlr^,::i -- i,.'tl*. 4l:9 ?t)f3' Y.r" ?ri'- ZJ 25 APPROXIMATI SCALE*FEET HIGHWAY 82 23-7 -1Bg Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING 1 BORING 2 0 0 e/6,27/6 11/12 WC=6,3 DD=9 1F LrlU L! IIF o_u 5 ( F Ld LJ LL IIFo-tJo 88/12 WC= 1 .0 +4=53 -2O0=1 1 1o/6,2e/6 10 10 23-7 -189 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 :l LEGEND TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, VERY MOIST, BROWN CLAY AND SILT (CL_ML); SANDY, SCATTERED GRAVEL, STIFF, SLIGHTLY MOIST, BROWN. mr,t4 [7il cnavrl AND coBBLES (GM-Gp); slrcHTLv srLTy, sANDy, pRoBABLE BoULDERS, DENSE, lj":4iSLTGHTLY MorsT, RED-BRowN, RoUNDED RocK. DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE I DRTVE SAMPLE, 1 5/8-tNCH LD. SPLTT SPOON STANDARD pENETRAT|0N TEST 38/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 38 BLOWS OF A 14O_POUND HAMMER FALLING 30 INCHES WTRE REQUIRED TO DRIVE THE SAMPLER 12 INCHES, i PRACTICAL AUGER DRILLING REFUSAL. NOTES THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 16,2023 WITH A 4_INCH DIAMETER CONTINUOUS_FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FTATURES SHOWN ON THE SITE PLAN PROVIDTD. 3, THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OFTHE EXPLORATORY BORINGS ARE PLOTTED TO DEPTH. 4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED, 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE APPROXIMATE BOUNDARIES BTTWEEN MATERIAL TYPES AND TI-IE TRANSITIONS MAY BE GRADUAL. 6, GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (pcf) (ASTM D2216); +4 = PTRCENTAGE RETAINED oN No. 4 SIEVE (ASTM D6913); -2OO = PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1140) 23-7 -189 Kumar & Associates LTGIND AND NOTTS Fig.3 2 0 -1 -4 J J td =a I zo F o Ioazo C) 6 -8 1 0 1 2 1 4 *16 -18 -20 1.0 APPLIED PRESSURE - KSF 10 100 SAMPLE OF: Sondy Silt ond Cloy FROM:Boring2@2.5' WC = 6.3 %, DD = 91 pcf in ond tusociotes, lnc. Swell ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 2s-7 -189 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 4 TIME READINGS U.S. STANDARD STRIES CLEAR SOUARE OPENINGS 100 90 ao 70 60 50 40 50 20 HRS 7 HRS MIN 15 MIN 6OMIN 19MIN 4MIN IMIN * 1.Oo l:o #14 ,5q 116 *1O #a 3/9"3/1" 1 1" : o 10 30 10 50 60 70 4 i, = ri : i i80 : :i1 ', -,- -: 90 ...1....:1..1. I ljlll...'.... : roo38.1 76.2 127. ZOO I ::l ...1 ...11... t.. 1.. I lil4.75 9.5 : ..:.r. 19 o:. :....1. I : l.ll l il .1.:.1 I llilll.oo1 .oo2 -oo5 .oo9 .o19 .o37 -o7s ,..1... i..1 1..:...llll i.150 .500 : .600 1.la -125 2-O 152 DIAMETER OF P ARTICLES IN MI SAN DCLAY TO SILT COBBLES GRAVEL 53 % SAND 36 LIQUID LIMIT SAMPLE OF: Sllghtly Silty Sondy Grcvel PLASTICITY INDEX SILT AND CLAY 11 % FROM:Boringl@5 Th€s€ lesl rssulls opply only lo th€ sompl6s whlch w€r€ l€sl€d. The iosllng reporl sholl nol b€ reproduc6d, sxc€pl in Iull, vilhoul lh€ wrillon qpprovql of Kumor & Assoclol€s, lnc, Sl€v€ onolysls losllhg ls pertorm€d In occordohc€ wilh ASTM D6915, ASTM 07928, ASTM C136 ond/or ASTM Dt'140. GRAVEL FINE MEDTUM lcoansrl nNE COARSE 23-7 -1 89 Kumar & Associates GRADATION TEST RTSULTS Fig.5 K-hnfffi'ffimffi,Yr;***** TABLE 1 SUMMARY OF LABORATORY TEST RESULTS No.23-7-189 2 I BORING 2% 5 lfr) DEPTH SAMPLE LOCATION 6.3 1.0 (a\ NATURAL MOISTURE CONTENT 91 NATURAL DRY DENSITY locfl 53 (%) GRAVEL 36 SAND $t GRADATION 11 PERCENT PASSING NO. 200 sIEVE (%l LIQUID LIMIT PLASTIC INDEX ATTERBERG LIMITS {psf} UNCONFINED COMPRESSIVE STRENGTH Sandv Siit and Clav Slightly Silty Sandy Gravel SOIL TYPE