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Home My WebLink AboutSubsoil StudyI (trt iitiïfi'trl'fÉ:fr'rËnå' n " " RECEIVED JUN Ü $ 2ü22 GARFIELD COUNTY COMMUNITY DEVELOPMENT An Employcc Owncd Compony 5020 County Road 154 Glenwood Springs, CO 8 l60l phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com www.kumamsa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado October 7,202I Barrett Cyr P.O Box 9064 Aspen, Colorado 81612 barrett@cyrandcompan)¡. com Project No. 21-7-620 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 6, St. Finnbar Farm, St. Finnbar Farm Road, Garfield County, Colorado Dear Barrett: As requested, Kumar & Associates, lnc. 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 you dated July 20,2021. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: We understand the house will be one story of wood frame construction, located in the area of Pits I and2 as shown on Figure 1. Ground floor will be slab- on-grade in the garage or structural over a shallow crawlspace. Cut depths are expected to range between about2 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 site is vacant and relatively flat with a slight slope down to the southwest toward the Roaring Fork River located south of the building area. Vegetation in the building area consists of grass and weeds with scattered small willow trees. We understand the building area elevation is above the 1O0-year flood plain. 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 lYzfeet of topsoil, consist of 2Yz feet of soft, sandy silty clay overlying relatively dense, slightly silty sandy gravel with cobbles and small boulders down to the bottom of the pits at 5 feet. Ground water was observed ., in the bottom of the pits at 4 feet deep. Results of a swell-consolidation test performed on a sample of the sandy silty clay obtained from Pit I are presented on Figure 3 and indicate moderate to high compressibility under loading and wetting. The soils above the ground water were moist to very moist. 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 designed for an allowable soil bearing pressure of 1,000 psf for support of the proposed residence. The topsoil should be removed from the building area. The clay soils are highly moist and the exposed grade could need stabilization such as with geogrid and aggregate base. Footings should be a minimum width of 20 inches for continuous walls and 2 feet 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 clay soils. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at least 36 inches below the exterior finish 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 be designed to resist alateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site clay soil as backfill. Floor Slabs: 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 slabs to facilitate drainage. This material should consist of minus 2-inch aggregate with less than50Yo passing the No. 4 sieve and less than2Yo passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least95Yo of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of a suitable imported gtavel devoid of vegetation, topsoil and oversized rock. Kumar & Associates, lnc. @ Project No. 21-7-620 -3- Groundwater: Due to the risk of wetting from the nearþ river and the relatively shallow ground water associated with it, we recommend that the crawlspace grade be elevated as much as possible. A perimeter drain system is not required for the shallow crawlspace or garage slab-on- grade provided foundation wall backfill is properly placed and compacted with a positive surface slope away from the foundation. 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 90%o 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 l0 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in pavement and walkway areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 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 pits excavated at the locations indicated on Figure I 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 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 re-evaluation of the recommendations 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 Kumar & Associates, lnc. @ Project No, 21-7-620 -4- should provide continued consultation and field services during construction to review and monitor the implementation of our recommendations, and to verifu 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 beming strata and testing of structural till 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 & Associateso lhc. Daniel E. Hardin, P Rw. by: SLP DEHlkac attachments Figure 1 - Location of Exploratory Pits Figure 2-Logs of Exploratory Pits Figure 3 - Swell-Consolidation Test Results Kumar & Associates, lnc. ''ProJect No. 21"7.620 TO ST. FINNBAR FARM ROAD 100 0 0 APPROXIMATE SCALE-FEET 21 -7 -620 Kumar & Associates LOCATION OF TXPLORATORY PITS Fig. 1 E E I 9 PIT 1 PIT 2 0 0 Ft¡J t¡Jt! I-Fo- TJô WC= 1 9.1 DD=80 t- L¡Jtd LL I-FILtJo 5 5 LEGEND TOPSOIL; ORGANIC SANDY CLAYEY SILT, WITH ROOTS, SOFT, MOIST, DARK BROWN CLAY (CL); SILTY, SANDY, MEDIUM STIFF, MOIST TO VERY MOIST, BROWN. GRAVEL (GM_GP); WITH COBBLES AND SMALL BOULDERS, SANDY, SLIGHTLY SILTY, MEDIUM DENSE TO DENSE, WET, BROWN. F HAND DRIVE SAMPLE. I oeprg ro wATER LEVEL ENcouNTERED AT THE TIME oF EXcAVATToN ---> DEPTH AT WHICH PIT CAVED. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JULY 20,2021. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEAÏURES SHOWN ON THE SITE PLAN PROVIDED. 5. THE ELEVATIONS OF ÏHE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE EXPLORATORY PITS ARE PLOTTED TO DEPTH. 4. THE EXPLORATORY PIT LOCATIONS 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. GROUNDWATER 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 Ð 2216): DD = DRY DENSTTY (pct) (nSrU D 2216). a' b/.'y': 21 -7 -620 Kumar & Associates LOGS OF EXPLORAÏORY PITS Fig. 2 I I I I SAMPLE OF: Sondy Silty Cloy FROM:Pit1q^2' WC = 19.1 %, DD = 80 pcf { I I ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING \ l ftar€ tæt Éaulb opply oñly to th€smpl.r t.!bd. ft. bstlng r.Fd rholi not h r.prcduccd, .xc6pt in full, rlthout thâ údtr n dpprcvdl of Küñdr ond &Bôcl6tð, lnc. Srrll Consolldotloñ t6t¡n9 pârfômâd ¡n occodonc€ with ffi D-4546, ¡ I l ) L l i l.- 0 -1 ,^-2 j-s l¡J =tJ1 t-4 z.ot- ô Jo(/) z,o<)-6 -7 -8 -9 -10 t t.0 APPLIED PRESSURE - KSF 10 t00 21 -7 -620 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3