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Home My WebLink AboutSubsoils Study for Foundationl(+rt$}ffiiffitrffi:x'å** ån Emþfcc ûmçct Cocnpanf 5020 County l{oad 154 Glc'nrvood Splings, C() 81601 phone: (970) 945-7988 fax: (970) .945-8454 email: kaglenwood,@ìkurnarusa.cont rv lv w.kurnarusa. ccxlt Office Location-s: Denver (IIQ), Parker, Colorado Springs. Fort Collirs. Glenr.l'oul Springs. antl Surunit Cormty, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT H19, THE HOMESTEAD ASPEN GLEN 55 HORSESHOE LANE GARFIELD COUNTY, COLORADO PROJECT NO.21-7-397 JULY 02,2021 PREPARED FOR: MIC MOUNT 580 WEIDMAN COURT LAKE OS\ryEGO, OREGON 97034 m icm ou n t@,com c.ast. net TABLE OF'CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SI'Ih, CONDI'ITONS SUBSIDENCE POTENTIAL FIELD EXPLORATION ...... SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS FOUNDATION AND RETAINING WALLS FLOOR SLABS UNDERDRAIN SYSTEM SURFACE DRAINAGE................ FIGURE I - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESIILTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS -3- a ., -)- 7- I 1 1 Kumar & Associates, lnc. @ Project No.21-7-397 PURPOSE AND SCOPE OF'STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot H19, The Homestead, Aspen Glen, 55 Horseshoe Lane, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in accordance with our proposal for geotechnical engineering services to Mic Mount dated April 13,202I- A fîeld exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classifrcation, compressibility or swell and other engineering characteristics. The results of the field exploration and laboratory testing were analyzed to develop recommendations for foundation types, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conclusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION Plans for the proposed residence were not available at the time of our study. The proposed residence will be a one- and two-story structure with attached garage. Ground floor will likely be a combination of structural over crawlspace and slab-on-grade. Grading for the structure is assumed to be relatively minor with cut depths between about 2 to 4 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITIONS The subject site was vacant at the time of our field exploration. The ground surface is gently sloping down to the northeast at an estimate grade of about 5 percent. Vegetation consists of grass and weeds. Bedrock of the Eagle Valley formation outcrops southwest of the site and the Maroon Formation outcrops to the northwest. Kumar & Associates, lnc- o Project No. 21-7-397 a STIBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen development. These rocks are a sequence of gypsit'erous shale, tîne-grained sandstone and siltstone with some massive beds of gypsum and limestone. There is a possibilify that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, several sinkholes were observed scattered throughout the Aspen Glen Subdivision. The nearest mapped sinkhole is about 2300 feet southeast of this lot. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork Valley. Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities was encoltnterecl in the subsurface materials; horvever, the exploratory borings were rolatively shallow, for foundation design only. Basecl on our present knowledge of the subsurface conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of future ground subsidence on Lot Hl9 throughout the service life of the proposed residence, in our opinion, is low; however, the owner should be made aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. F'IELD EXPLORATION The field exploration for the project was conducted on ll4ay 4,2021. Tltree 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 taken with l%-inch and 2-inchl.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 simiiar to the standarci penetration test described by ASTM Method D-1536. The penefrafion resistance values al'e an indication of the relatir¡e density or consistency of the subsoils. Depths at which the samples were taken and the penetration resistance values are shown on the Logs of Exploratory Borings, Figure 2. The somples wcrc rcturncd to our laboratory for review by the project engineer and testing. Kumar & Associates, lnc. o Project No. 21-7-397 -3 - SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about Yz foot of topsoil overlying 14 to 15% feet of stiff, sandy silty clay soils over dense, sandy gravel with cobbles down to the maximum explored depth of l7V'to lSVzfeet. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and possible boulders and drilling refusal was encountered in the borings. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and percent finer than sand grain size gradation analyses. Results of swell- consolidation testing performed on relatively undisturbed drive samples, presented on Figure 4, indicate low to moderate compressibility under existing low moisture conditions and light loading and a varied low expansion or moderate collapse potential when wetted under constant light surcharge. Our experience in the area indicates that the expansion potential is probably an anomaly and can be discounted for foundation design. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist to moist. F'OUNDATION BEARING CONDITIONS The upper sandy clay soils encountered at the site typically possess a low bearing capacity and low to moderate settlement potential when wetted. The underlying gravel soils have a moderate bearing capacity and typically low settlement potential. The proposed residence can be founded with spread footings bearing on the upper clay soils with a risk of foundation movement particularly if the bearing soils become wetted. Providing proper surface drainage around the residence to reduce the risk of subgrade wetting is recommended. Providing a depth, typically 3 feet, of moisture conditioned and compacted structural fill below spread footing would reduce the risk of foundation movement. Structural fîll can probably consist of the onsite soils moisture conditioned to slightly above optimum moisture content and compacted to 98 percent of maximum standard Proctor density. If structural fill is proposed we should be contacted during excavation to observe the onsite soils and assess their suitability as structural fill. A lower risk option would be to extend the foundation bearing level down to the underlying dense gravel soils with a deep foundation system such as helical or drilled piers. Provided below Kumar & Associates, lnc. @ Project No. 21-7-397 4 are recommendations for a spread tboting toundation system. If rocommendations for a deep foundation system are desired, we should be contacted to provide them. DE,STGN RIJCOMMENDATTONS FOI.INDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, the building can be founded with spread footings bearing on the natural soils with a risk of foundation movement. The design and construction criteria presented below should be observed for a spread footing fbundation system. l) Footings placed on the undisturbed natural soils shoulcl be clesigned for an allowable bearing pressure of 1,500 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. There could be some additional settlement if the bearing soils become wetted. The magnitude of additional movement would depend on the depth and extend of wetting but could be on the order of about 1 inch. 2) The footings should have a minimum width of 18 inches for continuous walls and 2 feet for isolatcd pads. 3) Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at lcast 36 inches below exterior grade is typically used in this area. 4) Continuous foundation walls should be well reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 teet. Foundation walls acting as retaining structures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) Topsoil and any loose disturbed soils should be removed and the footing bearing level extended down to the firm natural soils. The exposed soils in footing area should then be moistened and compacted. 6) A representative ofthe geotechnical engineer should observe all footing excavalions prior to concrete placement to evaluate bearing conditions. Kumar & Associates, lnc. @ Project No. 21-7-397 -5- FOUNDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for alateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 50 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are separate from the residence and can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 40 pcf for backfill consisting of the on-site clay soils. Backfill should not contain vegetation, topsoil or oversized rock. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, trafftc, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Foundation wall backfill should be placed in uniform lifts and compacted to at least 90% of the maximum standard Proctor density at a moisture content near optimum. Backfill in pavement and walkway areas should be compacted to at least95Yo of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.30. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The coefficient of friction and passive pressure values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to limit the strain which will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be compacted to at least 95o/o of the maximum standard Proctor density at a moisture content near optimum. Kumar & Associates, lnc. @ Project No. 21-7-397 -6- FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction. The clay soils are compressible, which could result in some slab settlement and distress if the bearing soils become wetted. To reduce the effects of some differential 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 for joint spacing and slab reinforcement should be established by the designer based on experience and the intended slab use. A minimum 4-inch layer of relatively well graded sand and gravel, such as road base, should be placed beneath slabs for supporl. This tnaterial should consist of rrrirrus 2-inch aggregatc with at lcast 50olo rctained on the No. 4 sieve and less than lZYo passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 957o of maximum standard Proctor dcnsity at a moisture content near optimum. Required fill can consist of the on- site granular soils devoid of vegetation, topsoil and ovorsized rock. We recommend vapor retarders conform to at least the minimum requirements of ASTly'rEL745 Class C material. Certain floor types are more sensitive to water vapor transmission than others. For floor slabs bearing on angular gravel or where flooring system sensitive to water vapor transmission arc utilizcd, wc rccommcnd a vapor barricr be utilized conforming to the minimum requirements of ASTM 81745 Class A material. The vapor retarder should be installed in accordance with the manufacturers' recommenclations ancl ASTM 81643. UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our experience in the area, and where clay soils are present, that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can crcate a perched condition. We recommend below-grade construction, such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. Crawlspace areas shallower than about 4 feet should not need an underdrain provided exterior backfill is properly compacted and a positive surface slope is maintained away from the residence. If installed, the drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free-draining granular material. The drain should be Kumar & Associates, lnc. @ Project No. 21-7-397 -7 - placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum lo/o to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2o/o passing the No. 200 sieve, less than 50% passing the Nó. 4 sieve and have a maximum size of 2 inches. The drain gravel backfrll should be at least 1t/zfeet deep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. SURFACE DRAINAGE Proper surface drainage will be critical to the long-term satisfactory performance of the proposed residence. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation ofthe foundation excavations and underslab areas should be avoided during construction. 2) Exterior backfrll should be adjusted to near optimum moisture and compacted to at least 95o/o of the maximum standard Proctor density in pavement and slab areas and to at least 90Yo of the maximum standard Proctor density in landscape areas. 3) The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of 6 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. Free-draining wall backfill should be covered with filter fabric capped with about 2 feet of the on-site soils to reduce surface water infi ltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least 5 feet from foundation walls. LIMITATIONS 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 this report are based upon the data obtained from the exploratory borings drilled at the locations indicated on Figure 1, the proposed type of construction and our experience in the area. Our services do not include determining the Kumar & Associates, lnc. o Project No. 21-7-397 -8- prssence, prevention or ponsihility *f mnlcl çr *ther biological contaminants (MOBC) dcvclopínfi in the firrure. If the client is cçncerned atrout MÕBC, then n professionnl in this npecial lÌcicl of prnctice should be consr*ted, {h¡r finelings include interpolafior} flnd extrâpolntion of the subsurfrrce conditions identifïed at the explaratory borings and variations in the sub*urface conrlitians may nnt hecnmc evidcnt until cx*nvation is perfnrmed. If conditic¡n$ enrounterod during consfuction åpperir different ilom those described in this rryorto we should be notified so that re-evaluation of the recammendations may be madc. This report has been prepared for the exclusive use by osr clisnt f*rr design purpöss$. We are not responsible far technical interpretations by others af CIur infonnation. As the pmject everlves, we should prorride continued consultation md field servicen duriug cçrutrustiun to reviow and manitor the implømentation of our recommendaticns, and ta v*rifu that the recommendations have been appropriately inteqpreted. Significant design changen may require additianel analysis or modifications to the resommendations presented herein, Vy'e recommend on-nite observafion of excavatíons and foundation bearing strata and testing of strucf¡ral fill by a representative of the geoteehnic*l engineer. Respectfirlly Submitted, Ktgmnr & ,4sro*i.æËssu ïn*" James H. Farsons, P.B. Reviewed by: Daniel Ë. Hardin, P"E. JHP/kac Kumar * Å*socÈatæ, !ne. s Frnjoc{ Ho. ?t-?"å$? t Ë vI t I \n- { .,,*ï^dþ'. "k;+- t{---t å BENCHIIARK lOO'ASSUMED FlwLnç -/ -r'r'./'1 -- -- -.r*ou#* .å\Jfu"' "ô .\o' ÉËd. s 68"36'36'E \ Êd.eç ofÃsphæ& ?*p eatk af Curb @ Çr* \ \\ 2 APPROXIMATE SCALE-FEET ffi 24.t', ><l\ -alê"'- \ -* \¿\ \¡ BORING f \\ Fô¿¿nd lÉ.t.Xsþar 3A, I-¿ 0' !,ot HÍ9 Åspen $Ien Filíng No. 7 Retx.¡rtron .lïo. 5525Ð6 BORING 2 \o 55 *lorsøshçe LøîÆ vscüft| Leftd P.66¡t ¿æs 5 _) j- / *b2âq6'n r*#'Y- -, -1 "20.4' ;- - ta. ,.**# \ 21 -7 -397 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 d BORING 1 EL. r 05' BORING 2 EL. 109.5' BORING 5 0 0 5 515/12 WÇ=5.1 DD= I 08 -200=65 6/12 WC=l DD=9 1.8 6 t- l¡JulL ITt-o-l¡lo 10 10 Fl¿ll¡l 14 I- o- l4lô 23/12 WC=5.6 DD=1 1 5 17 /12 WC=7.6 DD= 1 05 -2OO=74 15 50/5 1534/12 WC=5.6 DD=1 14 -200=54 1oo/6 ?o 20 21 -7 -397 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 â LEGEND TOPSOIL; CLAY, SILTY, SLIGHTLY SANDY, ORGANICS, FIRM, SLIGHTLY MOIST, ÏAN CLAY ( MOIST, CL); SLIGHTLY SANDY, SCATTERED GRAVEL, STIFF TO VERY STIFF' SLIGHTLY TAN. GRAVEL (GM); SILTY, SANDY, COBBLES, DENSE, SLIGHTLY MOIST, BROWN. DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE. ¡ DRTVE SAMPLE, 1 s/ï-INCH l.D. SPLIT SPOON STANDARD PENETRATIoN TEST. ..1.â DRIVE SAMPLE BLOW COUNT. INDICATES THAT f5 BLOWS OF A I4O-POUND HAMMER 'ul '' FAtLrNc 50 rNcHEs wERE REQUIRED To DRtvE THE SAMpLER t2 tNcHEs. I PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON MAY 4, 2021 WITH A 4-INCH-DIAMETER CONTINUOUS-FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER TO THE BENCHMARK ON FIG. 1. 4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY TIIE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN TIIE BORINGS AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: wc = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (pcf) (ASTM D2216)t -200= PERCENTAGE PASSING N0. 200 SIEVE (ASTM 01140)' 21-7-397 Kumar & Associates LEGEND AND NOTES Fig. 5 I d æ,CoNSoLTDATTON - SWELL (%)'!loNI(¡(¡oE!trFEãään5P(¡ @ rtlb,9o+llNdeEso<r-gt<îrC)('Orrt¡ããË8øcovz.rrtcC.Z3B2.7ñ812.1ut,ãi-{/A\åea-;-r3 *o 99'áo gè5sl I*;fÍ¡ FËffiå*ç" 9.rlãì.)I\¡I(,¡rc)\¡^g30,eoØ(noc).q)oaUI=rflt-t-Ic)oz.V'ot-oÞ-{oz.-{rrlUI-{vmU'ct--{art(os t SAMPLE OFr Sondy Cloy FROM¡BorlngS@5' WC = 11,8 %. DD = 96 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING \ \ \ \ \\ I \ \ \ \ I I¡ã t ülÐ a9py onry þ uaæñd6 t rtad. tlìa batlnt Fprt ¡holf nd b npıds€d, .xflpt ln lull, xlthout tù. rrllt n opryl ol Klmar ond Aedotar, |rc, Srall tunslldollon tóllno [lomad ln looñldnd rlth Æ'h¡ D-1ı.t6. 1 0 ^-1>s JJ-z l¡J tn r_3 zo Fj-+ otnz,oo-s -6 -7 -8 -9 APPLIED PRESSURE - KSF 10 21 -7 -397 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fis. 5 t(+rtfsrs&Aæffi,k¡s.*G*tå$ilicâ, ard Malerials Enginee*and ãnvironm*nbl Scier¡tbtsTABLE 1SUMMARY OF LABORATORY TEST RESULTSJIBORINGl05I5I05fft)DEPTHSA¡IPLE LOCATIO]I7.6I115.65.65IP/o\ilAruRALiIOISTURECOHTENT10s96114113108focfìNATURÁI-DRYDENSITY(vtGRAVELSAND(:/":,GRADATION745465LIQUID LI[IITPERCENTPASSING NO.200 stEvEPLASTICINDEXUITICONFINEDCOHIPRESSIVESTREI{GTHSandy ClaySrurdy ClaySand and ClayVery Sandy ClayVery Sandy ClaySOIL TYPEtlo.21-7.397