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Home My WebLink AboutSubsoil Studyl(trt l(umar & Associatæ, lnc. Geolechnical and Materials Engineers and Envkonmental Scientists 5020 County Road 154 Glenwood Spri phone: co 81601 945-7988 ngs, (e70) fax: (970) 945-8454 email: kaglenwood@kumarusa.com An Employcc Olvncd Compony www'kumarusa'com Offìce Locations: Denver (HQ), Parker, Colorado Spr¡ngs, Fort Collins, Glenwood Springs, and Summit County, Colorado June22,2020 Sunrise Company Attn: Teddy Farrell 0115 Boomerang Road, Suite 52018 Aspen, Colorado 81611 tfarrell@sunri seco.com Subject: Project No.20-7-332 Subsoil Study for Foundation Design, Proposed Residence, Lot E-13, Aspen Equestrian Estates,4T Equestrian Way, Garfield County, Colorado Gentlemen As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at the subject site. The study was conducted in accordance with our agreement for geotechnical engineering services to Sunrise Company dated June 9,2020. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: Development plans for the lot were not available at the time of our study and our frndings will be considered in the purchase of the lot. We assume the proposed residence will be a one or two-story structure with an attached garage located within the building envelope shown on Figure 1. Ground floor could be structural over crawlspace or slab-on-grade. Cut depths are expected to range between about 2 to 3 feet. Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction. If building conditions or foundation loadings are significantly different from those described above, we should be notified to re-evaluate the recommendations presented in this report. Site Conditions: The lot was vacant at the time of our site visit. The lot is flat, slopes slightly down to the south and is vegetated with grass and weeds. A marshy area is located directly north of the lot. Eagle Valley Evaporite bedrock is exposed on the valley hillsides to the north and south. Subsidence Potential: Aspen Equestrian Estates is underlain by Pennsylvania Age Eagle Valley Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution of the gypsum under RECËIVED GARFIË,LD COUNTY COMMUNITY DEVELOPMENT a-L- certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, sinkholes were observed in this part of the Roaring Fork River valley but not in Aspen Equestrian Estates. Sinkholes or indications of surface subsidence or subsurface voids were not observed in the immediate area of the subject lot nor encountered in the exploratory pits dug on the lot. Based on our present knowledge of the site, it cannot be said for certain that sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot E-13 throughout the service life expectancy of the residence is low and similar to other lots in the area but the owner should be aware of the potential for sinkhole development. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below about one foot of topsoil, consist of medium stiff, sandy silty clay to a depth of about 4t/z feet. Relatively dense, slightly silty sandy gravel and cobbles was encountered below the clay to the maximum explored depths of 5%to 6 feet. Results of swell-consolidation testing performed on relatively undisturbed samples of sandy silty clay, presented on Figures 3 and 4, indicate low compressibility under existing moisture conditions and light loading and moderate compressibility when wetted and subjected to increased loading. Free water was observed in Pit I at a depth of about 4Yz feet and in Pit 2 at a depth of about 3 feet at the time of excavation. The upper soils were very moist to wet with depth. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placed on the undisturbed natural clay soil below the topsoil designed for an allowable soil bearing pressure of for of the propo sed residence. Footing depth should be 2 to 3 feet below surface to avoid soft wet soils. Soft subgrade soils could need localized stabilization such as with geogrid and around 12 inches of CDOT Class 2 (minus 3-inch) base course. We should observe the bearing soils within the excavation prior to forming for footings. The clay soils tend to compress when loaded and there could be post-construction foundation settlement of around I inch. Footings should be a minimum width of 20 inches for continuous walls and 2 feet for columns. The topsoil and loose disturbed soil 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 frost protection. Placement of Kumar & Associates, lnc.Project No. 20-7-332 a-J- footings at least 36 inches below the exterior grade is typically used in this area. Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining structures should also be designed to resist alateral earth pressure based on an equivalent fluid unit weight of at least 55 pcf for the on-site soil as backfill excluding organics and rock larger than 6 inches. Floor Slabs: Slab-on-grade main floors are recommended to avoid moisture associated with crawlspaces where groundwater is shallow. The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction. 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 free-draining gravel should be placed beneath interior slabs to facilitate drainage. This material should consist of minus 2-inch aggregate with less than 50Yo passing the No. 4 sieve and less than2o/o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95%o of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the onsite soils devoid of vegetation, topsoil and oversized rock. High moisture clay soils could require drying before placing as structural fill. We recommend vapor retarders conform to at least the minimum requirements of ASTMEI745 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 are utilized, we recommend a vapor barrier be utilized conforming to the minimum requirements of ASTM 81745 Class A material. The vapor retarder should be installed in accordance with the manufacturers' recommendations and ASTM 81643. Underdrain System: Free water was encountered during our exploration and it has been our experience in the area that the groundwater level can rise during irrigation season. We recommend below-grade construction, such as retaining walls and crawlspace areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. The underdrain should not be needed ifthe ground floors are slab-on-grade elevated above the surrounding area. Kumar & Associates, lnc.Project No. 20-7-332 -4- The drains should consist of rigid perforated drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free-draining granular material. The drain should be placed af each level of excavation and at least I foot below lowest adjacent finish grade and sloped at a minimumY'o/o to a suitable gravity outlet or sump and pump. 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 No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least lYz feet deep. Surface Drainage: 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 backfill should be adjusted to near optimum moisture and compacted to at least 95%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. Free-draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration. 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 l0 feet in unpaved areas and a minimum slope of 2Yz inches in the first l0 feet in pavement and walkway areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy iruigation should be located at least 5 feet from the building. Limitations: This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area atthis 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 pits excavated at the locations indicated on Figure 1 and to the depths shown on Figure 2, the proposed type of construction, and our experience in the area. Our services do not include determining the presence, prevention or possibility of mold or other biological contaminants (MOBC) developing in the future. If the client is concerned about MOBC, then a professional in this special field of practice should be consulted. Our findings include interpolation and extrapolation of the subsurface conditions identified at the Kumar & Associates, lnc.Project No. 20-7-332 5 exploratory pits and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear different from those described in this report, we should be notified at once so rq-evaluation of the recomrnendations may be made. This report has been prepared for the exclusive use by our client for design purposes. We are not responsible for technical interpretations by others of our information. As the project evolves, we should provide continued consultation and field services during construction to review and monitor the implementation of our recommendations, and to veriff that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications 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. If you have any questions or if we may be of further assistance, please let us know. Respectfully Submitted, Kumar & Associates, Inc. Steven L. Pa Reviewed by: Ç )/'-*/*" Daniel E. Hardin, P.E. SLPlkac Attachments: Figure I - Location of Exploratory Pits Figure 2 - Logs of Exploratory Pits Figures 3 and 4 - Swell-Consolidation Test Results Table 1 - Summary of Laboratory Test Results Kumar & Associates, lnc.ProjectNo. 20-7-332 9 WC. TO fiE NE CORNËR oF sEc, J1 (STONE) W¿Yo, r',E SUBDIVSìON COMMON AREA/OPEN SPACE 610,S4 S,F,}l¡.0t0 ^c1 .sJár€H!.g.flJvAY82 2 si/ðÒ/øs/o& I 9l¡ Els 9r i \, 'P'!,ff¡¡¡v^ou, .ICH AT RING t& \ Â lY¡l'..- - \lr ST. FINNEARR {"r <q ı ì w LEGEND: +BENCHMARK MANHOLE RIM EL. 1OO" ASSUMED. 1 APPROXIMATE SCALE-FEET ---ioÌil:i--*- is,o55 sa.Fr] i o6ae ^c.+ i @¡ @ @ LOI Et4 I LALEg @ LOT EA it(o n o I, 8i ig öR ',', @ tsf-tz !aÏ,EE @ @ 20-7 -332 Kumar & Associates LOCATION OF EXPLORATORY PITS 1Fig. I ! PIT 1 EL. 1 01 .5' Ptl 2 EL. 105.5' 0 0 WC= 14.6 DD= 99 F t¡J tJJ L! ITt-(L UJo WC=21.5 DD= 1 00 -2OO=7 4 UC= 1 ,200 ¡NC=22.6 DD=97 F. t¡J l,¡JL! I-t-(L tdo Ã E 10 10 LEGEND TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, BROWN CLAY (CL); SILTY, SANDY, MEDIUM STIFF, PLASTICITY. VERY MOIST TO WET WITH DEPTH, BROWN, LOW SAND, GRAVEL AND COBBLES (GM-GP); SLIGHTLY SILTY, DENSE, WET, BROWN, ROUNDED ROCK. - DEPTH TO WATER LEVEL ENCOUNTERED AT THE TIME OF EXCAVATION F HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JUNE 10, 2O2O. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO THE BENCHMARK ON FIG. 1. 4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUND WATER LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER CONDITIONS INDICATED. FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); -2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140); Uc = UNCONFINED COMPRESSIVE STRENGTH (psf) (ASTM D 2166) 20-7 -332 Kumar & Associates LOGS OF EXPLORATORY PITS Fi1. 2 SAMPLE OF: Sondy Silly Cloy FROM:Pit1E^2' WC = 14.6 %, DD = 99 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I \ \ I l¡.so t6st r.surts oPPry onry to th¿ samplcs tcatd. lh. tæting r.poñ sholl not b. roprcduccd, exc.pt ¡n full. vìthod tho sdttcn opprcvrl of(umor ond ßsociol.s. lnc, Sw.ll conEolìdotion test¡ng p.domêd in dccordonc€ B¡th ASil D-4546. 1 à( JJ l¡J =UI I zotr o JoØzo() 0 -1 -2 -3 -4 -5 -6 -7 APPLIED PRESSURE - KSF 10 100 20-7 -332 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3 I e I r I SAMPLE OF: Sondy Silty Cloy FROM:Pit2@-3' tNC = 22.6 %, ùD = 97 pcf NO MOVEMENT UPON WETTING I \ \ \ \I vdttôn opprcvol ol :onsolidotioñ te3ting pedomed in rccordoncê eith ßil 0-4546. 1 às JJ l¡J =UI I z.otr o =o anz.oo 0 -1 -z _z -4 -5 -6 -7 1.0 APPLIED PRESSURE - KSF t0 100 20-7 -332 Kumar & Associates SWELL-CONSOLIDAÏION TEST RESULTS Fig. 4 lcrtffiïfi#flfffil,,rËü**TABLE 1SUMMARY OF LABORATORY TEST RESULTSSandy Silty ClaySOIL TYPESandy Silty ClaySandy Silty Clay7,200lpsf)UNCONFINEDCOMPRESSIVESTRENGTHPhlPLASTICINDEXATTERBERG LIMITSLIQUID LIMIT(ololPERCENÏPASSING NO.200 stEVE74979910014.621.322.6J2J12(%)SAND$tGRAVELSAMPLE LOCATIONDEPTHPITNATURALDRYDENSITYNATURALMOISTURECONTENTNo.20-7'332