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HomeMy WebLinkAboutSubsoil Study for Foundation Design 04.02.2024I (lrt $;;e;l[#:T:ffin[$ i. *. An Smploys* O,*n6d Compeiny 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa.com O{fice Locations: Denver (HQ), Parker; Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado April2,2024 Jesse Schoeller 6501 County Road 170 Carbondale, Colorado 81623 j esse@fi ni shinstouchdirtworx. corn Project No. 24-7-196 Subject: Subsoil Study for Foundation Design, Proposed Residence, 6501 County Road 170, West of Panorama Ranch, Garfield County, Colorado Dear Jesse: 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 you dated March 20,2024. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: The proposed residence will be one stclry over crawlspace located near the middle of the lot. The septic system will be located about 100 feet to the southeast of the house on the site as shown on Figure 1. Ground floor will be structural over crawlspace. Cut depths are expected to range between about 2 to 4 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 a vacant pasture in rolling terrain vegetated with grass and sagebrush. The lot slopes gently down to the south in the building area. The house is in open grassland. The septic area is about 100 feet southeast of the house and transitions from grass to sagebrush. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits in the house area and one pit in the septic area at the approximate locations shown on Figure l. The logs of the pits are presented on Figure 2. The subsoils encountered, below about I to l% feet of topsoil, consist of stiff, slightly sandy silty clay. Results of swell-consolidation testing performed on relatively undisturbed samples of the silty clay soils, presented on Figures 3 and 4, indicate low compressibility under existing low moisture conditions and light loading and low to moderate compression potential when wetted. Results n-L- of a gradation analysis performed on a sample of slightly sandy silty clay (minus %-inch fraction) obtained from the site are presented on Figure 5. No free water was observed in the pits at the time of excavation and the soils were slightly moist to 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 soil designed for an allowable bearing pressure of1 psf for support of the proposed residence. The soils tend to compress after wetting and there could be some post-construction foundation settlement. Footings should be a minimum width of 18 inches for continuous walls and2 feet for columns. The topsoil, loose and disturbed soils and existing fill encountered at the foundation bearing level should be removed and the exposed soils moistened to near optimum and compacted. 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 grade is typically used in this area. Continuous foundation walls should be 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 a lateral earth pressure based on an equivalent fluid unit weight of at least 55 pcf for the on-site 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 beneath basement level slabs to facilitate drainage. This material should consist of minus 2-inch aggregate with less than 50o/o passing the No. 4 sieve and less than 2o/o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95o/o of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on-site soils devoid of vegetation, topsoil and oversized rock. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the area that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create 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. Kumar & Associates, lnc, @ Project No. 24-7-196 -3- The drains should consist of drainpipe placed in the bottom of the wall backfill surounded above the invert level with free-draining granular material. The drain should be placed at each level of excavation and at least I foot below lowest adjacent finish grade and sloped at a minimum Io/oto 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 50olo passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least l%feet 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: 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 95Vo of the maximum standard Proctor density in pavement and slab areas and to at least 90o/o 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 surounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in pavement and walkway areas. A swale may be needed uphill to direct surface runoff around the residence. 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 the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the foundation caused by inigation. Septic Area Testing: One profile pit was dug at the location shown on Figure 1. The soils exposed in the profile pit consist of 1 foot of topsoil overlying 7 feet of slightly sandy silty clay. Based on the subsurface conditions encountered, the tested area should be suitable for a conventional infiltration septic disposal system. A civil engineer should design the infiltration septic disposal system. 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 Kumar & Associates, lnc, @ Project No, 24-7-196 ^4- tire area" *ur sen'ices dc not includs det*rmining the presence, prevention or possibility *f mold or other bi*lcgical contarninalrts (MOBC) developing in the fi"leure. If the cli*nt is ca*eer:red about MOFC, then a pr*fessional in tbis sp*cial field of praetice should be *onsulted. Sur findings ineluds interpolaticn and extrapolatian of the subsurf,ace c*nditions identified at thc exptroratory pits and vadatians in the subsurfa*e c*nditions may not bccame evident until exeavati*n is perforrned. If *creditions enc*untered durtng construeti*il epp*ar different fr*m tlr*se deseribectr in this report,:v* should be nctified at *:lce sc re-evaluatioa of the reocmmendations may be made. This repart has been prepar*d f*r the exclusive use by aur client for design Farposes. We are not resp*nsible for teclurical intery:rctati*ns by ottrrer* *f our informaticn. As the pr*jeet evolves, we shauld pr*vide co*tinue*l eelnsultati$* and ficld sen'ioes during c*nstrtreticn to r*vicw and rnonitr:r the irnplem*ntati*n of our re*cncn*rldations, and to v*ri$ that the recomrnsRdations havs been appropriately i*terpreted. Significant design changes may r*quire additional analysis q:r m$ciificaticns t* the recommendations prcsented herein. We r*ecmntend an-site observation of *x*avations and faundali*ir beering strata and t*sting cf structriral fill by a repr*sentative *f the gcatechnie*l *ngineer. if you hav* any questions cr if we may be *f fuither assistanee, pl*ase let us know. Respeetfully Subruitted, Kurnar &ftsr*. h Daniel fi. Ffardin, F.E. Reviewed by: Stev*n L. Pawlak, DEF{/lca* attaehm*nts Figure i * Locatior: of Hxplor*tory Pits Figure 2 - t*gs of,Hxploratory Fits Figures 3 and 4 * Swell-Ccnsolidation Test Results Figure 5 * US$A Gradati*n Test Results Kumar & Assseiates, Ene.6 Projeet filo. *4-Ftr$S s t \r 650't cR 't70 APPROXIMATE SCALE-FEET 24-7 -196 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. F I lPiT-Tl n LEGEND HAND DRIVE SAMPLE. DISTURBED BULK SAMPLE lFtpl m -E -E WC=1o.1 DD=1 01 I WC=12.8 DD=84 WC=18.2 SAND=5 SILT=26 CLAY=59 10 F t TOPSOIL; ORGANIC SANDY SILTY CLAY, CLAY (CL); SILTY, SANDY, SLIGHTLY MOIST TO MOIST, STIFF, BROWN EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON M 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FRO FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE 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 GRADUA 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (PCt) (ASTU D 2216); SAND = PERCENT PASSING NO. 10 SIEVE AND RETAINED ON NO.525 SIEVE; SILT = PERCENT PASSING N0. 525 SIEVE TO PARTICLE SIZE .002MM; CLAY = PERCENT SMALLER THAN PARTICLE SIZE .002MM' 24-7 -196 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. SAMPLE OF: Silty Cloy FROM:Pil 1@5' WC = 1O.1 %, DD = 101 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I \ \) I APPLIED PRESSURE - KSF 100 E -1 -4 JJ lrJ =a I z.o F o =oaz.o C) Fig.SWELL_CONSOLIDATION TEST RESULTS24-7-196 Kumar & Associates fi ft I € I SAMPLE OF: Silty Cloy FROM:Pit2@4' WC = 12.8 %, DD = 84 pcf UNDER CONSTANT PRESSURE DUE TO WETTING ) (I \ \ \ \ \ I Thc6 t at 6uha apply only to th. dmpl4 l6t d. tha t dting roport lholl not bc roprcduccd, cxccpt in t!ll, vithout th. wdtt n oppDvol of Klmor ond A3.ociotc, lnc. Sucll Conlolidollon l6tlng p.rfom6d i. dccoddncc $th ASII, D-/t546. 100 JJ lrJ =a I z.otr o =otnz.o c) E -10 -12 -14 24-7 -196 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. I ! k * v l SIEVE ANALYSISHYDMET S 24 HR. 7 HR r t\.11N. 045 #140 #60 #35 *18 #10 3t4' 1 1t2', 3', 5" 6" 100 '10 ^- ,^,. -t a * -t-.' l't tt ---tt---ll, - .-.t.....1 _-. -...1t. 90 20 80 30 70 40 50 60 40 70 30 80 20 90 10 '100 0 .001 .002 .005 .009 .019 .045 106 .025 ,500 1,00 2.00 4.75 9,5 19.0 37.5 76.2 152 203 DIAMETER OF PARTICLES IN MILLIMETERS CLAY COBBLES GRAVEL O %SAND 5 YO stLT 26 0/o CLAY 69 % USDA S0lL TYPE: Slightly Sandy Silty Clay FR0M: Profile Pit at 4 to 5 Feet Deep clrz aFlre Fzlrctlr(I ()z6a o- Fzlrl OE LJ o_ SILT 24-7 -196 Kumar & Associates USDA GRADATION TEST RESULTS Fig.