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Home My WebLink AboutSubsoil StudyI(t f i;ffilfi'trfffß:i*¡'f3;å*'" 5020 County Road 154 Glenwood Splings, CO 81601 phone: (970) 945-7988 tàx: (970) 94s-8454 ernail : kaglenwood@kumarusa.com wrvw.kumarusa. comÅn Ernployee Onmed Cannplrny Of1ice Locations: Denver (HQ), Parker, Colorado Springs, Fort Collils, Glenrvood Sprirrgs, and Summit County, Colorado RECËIVED September 74,2020 RC schneider construction tìL'i' ì ii !'ii?? Attn: Bob Schneider GARFIELD couNTY 218 East Valley Road coMMuNlTY DEVEL0PMENT bhs.austinschneider@icloud.com Project No.20-7-427 Subject Subsoil Study for Foundation Design, Proposed Residence, Lot 83, Filing 7, Los Amigos Ranch, 1965 Elk Springs Road, 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 RC Schneider Construction dated July 28, 2020. 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 a two story, wood-frame structure with an attached garage located in the vicinity of the exploratory pits shown on Figure 1' Ground floor will be structural over crawlspace in the main residence and slab-on-grade in the garage. Cut depths are expected to range between about 2 to 8 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 notifred to re-evaluate the recommendations presented in this report. Site Conditions: The subject site is currently vacant. Topography at the site is moderately sloping terrain down to the south at about 5 to 10 percent slope. A rough graded road cuts across the center of the building envelope trending west to east. Vegetation at the site consists of native grass and weeds with sage brush. Scattered pinyon and juniper trees are present in the southern part of the building enveloPe. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating three exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are a presented on Figure 2. The subsoils encountered, below about I foot of topsoil, consist of about I foot of sandy clay overlying silty sand with gravel down to the maximum depth explored of 8 feet in Pits 7 and2 and 9 feet in Pit 3. The silty sand with gravel was directly below the topsoil in Pit 3. Results of swell-consolidation testing performed on a relatively undisturbed sample of silty sand, presented on Figure 3, indicate low compressibility under existing moisture conditions and light loading and a minor hydrocompression potential when wetted. Results of a gradation analysis performed on a sample of silty sand with gravel (minus 3-inch fraction) obtained from the site are presented on Figure 3. No free water was observed in the pits at the time of excavation and the soils were slightly 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 granular soil designed for an allowable soil bearing pressure of 1,500 psf for support of the proposed residence. The soils tend to compress after wetting and there could be sorne post-construction foundation settlement. Footings should be a minimum width of I 8 inches for continuous walls and 2 feet for columns. Loose and disturbed soils and clay soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural granular 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 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 alateral earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as backfill. Floor Slabs: The natural on-site granular 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' All fill materials for support of floor slabs should be compacted to at least 95Yo of maximum standard proctor density at a moisture content near optimum. Required fill can consist of the on- site subsoils or a suitable imported gravel such as 3/+-inchroad base devoid of vegetation, topsoil and oversized rock. Kumar & Associates, lnc. @ Project No. 20-7-427 -3- 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 runoffcan create a perched condition. We recommend below-grade construction, such as retaining walls and deep crawlspace areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. 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 placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum lYo to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2Yo passingthe 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 1%feet deep and covered with filter fabric such as Mirafi 140N or 160N. Surface Drainage: The following drainage precautions 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 during construction. 2) Exterior backfill 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. Free-draining wall backfill should be 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 l2 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' 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 arca 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 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 Kumar & Associates, lnc. @ Project No. 20-7-427 4 or other biological contaminants (MOBC) developing in the future. If the client is concerned about MOBC, then a professional in this special fïeld of practice should be consulted. Ow 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 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 ofexcavations and foundation bearing strata and testing ofstructural 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, Tdztmar & -A,ssoeiates,In*. Robert L. Duran, P Reviewed by: Daniel E. Hardin, P.E. RLDlkac attachments Figure 1 * Location of Exploratory Pits Figure 2 * Logs of Exploratory Pits Figure 3 * Swell-Consolidation Test Results Figure 4 - Gradation Test Results Table I - Summary of Laboratory Test Results îl$/ðû Kumar & Åssoeia?es, lne, @ Projeet l{a. 20"7"427 aa2aâ:tå^å?¿sq?I,t'¡'.'..rtrgåååfaI!>tof.+æ\Å,,rP¡þiiI*1ôdi!âill:t3áá¡4ttÃÊri3Þ lì.u?bf",{\¡sI\¿\3þrjN,<cr$¿J.\) 9-\V\re.\./ '--. .r'' ' \\' .r\8'\ \.ãf r d\'I ' E\¿:É r q-.r . :-\t, I "-,t. -^\I -C..\i.¡ìz:iftl- r:ı ,':'i{ \\ri_-â.'j- ,r Ñ¡î,Oú'i /-.cl1\.\t,,r'l'.ÊcäråãË-{Þ,(^oo.D.EÃox--lnU)rrnI¡rr-l-n(of-oC)-lOz.O-lrnX-Et-on--lOn-u-.1t/)^c3g)-AoU'@oa.9)o(nN)OI!IÈN)\¡ J ¿ s, PIT 1 EL 6851' PIT 2 EL 6855' PIT 5 EL 6837' 0 0 t- UJ lJJ l! I :Et-fL lJJo WC=10.4 DD=8 1 l-.- UJ L¡JtL ITt-(L L¡Jo 5 5 I WC=6.4 14=13 -200=50 10 10 LEGEND TOPSOTL; CLAY AND SILT, SLIGHTLY SANDY, FIRM, BROWN, SLIGHTLY ORGANIC ROOTS CLAY (CL); SLIGHTLY SANDY, STIFF, SLIGHTLY MOIST, LIGHT BROWN, SLIGHTLY CALCAREoUS. SAND BOULD (GM-ML); BASALT GRAVEL & COBBLES IN A SILTY SAND MATRIX, SCATTERED BASALT ERS, DENSE, SLIGHTLY MOIST, LIGHT TAN, CALCAREOUS. F t HAND DRIVE SAMPLE. DISTURBED BULK SAMPLE. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON AUGUST 24, 2O2O. 2. THE LOCATÍONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACINO FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 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 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)t DD = DRY DENSITY (PCT) (ASTU D 2216)" +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ISTU O ¿ZZ); -2oQ= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). 20-7 -427 Kumar & Associates LOGS OF TXPLORATORY PITS Fi1. 2 I SAMPLE OF: Silty Sond FROM:Pitl@5' WC = 10.4 %, DD = 81 pcf --r' I : I ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING DL appY onY to thr d, lha tEtlnq o9oñ rpEducd, .iclpt ln ú Wdlt.n opprcYol ot Eoclot r. lÉ S*.ll t rtl¡g. Flom.d ln th ÀStl¡ 0-,rð46. 1 0 J4J -ll¡J =vl t_2 zotr !-soØz.oQ-4 PRESSURE - KSF I 20-7 -427 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig.5 F J 2 g .l00 90 lo fo c0 50 10 JO 20 'lo 0 HYDROMETER ANALYSIS SIEVE ANÀLYSIS TIUE READINOS A4 HRS 7 HRs U.3. STANDAiO SERIES ¡(6 ¡b ¡{ñ ¡lt ¡lô ¡¡ CLEAR SQUARE OPENI}¡o5 SAND GRAVEL FINE MEDTUM lcoense FINE COARSE o l0 20 s0 4 50 60 70 l0 eo ioo I E Ë PA CIáY TO SILT COBBLES GRAVEL 13 % SAND LIOUID LIMIT SAMPLE OF: Sllty Sond wllh Grovel 57% PLASTICITY INDEX SILT AND CLAY 30 % FROM:Plt2O7'-8 th.!r lrll..rullt qpply only lo lhc ¡omoler whloh voru tottod, fh! t.¡fi;rg ruport ¡hqll nqt bc rcPrcduocd, .xo.pl ln full. Yllhoul lhl wrltton oooóvol ol Kumor & Artoolol¡r, lño' Sí¡lv¡ onolv¡l¡ l.tllno b Darform.d ln oooordo¡oå wllh aslM 0dgl5, ASTM 07928, Asfil cl56 ond,/or ASTM Dll.lo' 20-7 -427 Kumar & Associates GRADATION TEST RESULTS Fig. 4 l(+rtij|ffi,ffi'ffË**'TABLE 1SUMMARY OF LABORATORY TEST RESULTSSilty Sand with GravelSOIL TYPESilty Sand{osfìUNCONFINEDCOMPRESSIVESTRENGTH(%lPLASTICINDEXATTERBERG LIMITSIololLIQUID LIMIT30PERCENTPASSING NO200 sIEVE57SAND(%)3IGRADATION$tGRAVELI8NATURALDRYDENSTTYlpcf)6.4(%lNATURALMOISTURECONTENT10.47-8tft)DEPTHJPITI2SAMPLE LOCATIONNo.20-7-427