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Home My WebLink AboutSubSoil Studylc i#iftå1'ffË:Fjf,'lÊü,** An Employee Owned Compony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com www.kumalusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado October 5,2021 Red House Architecture Attn: Bruce Barth 815 Blake Avenue Glenwood Springs, Colorado 81601 bruce@redhouserchitecture. com tNlvud0l3^ã0 ^rlN nny{09 ^INnOC 013|JUV0 r¿0¿ [ [ LJO g3^lãÐãu Project No. 2l-7-660 Subject: Subsoil Study for Foundation Design, Proposed Merriman Residence, Lot29, Filing 9, Elk Springs, Kingbird Drive, Garfield County, Colorado Gentlemen: As requested, Kumar & Associates, [nc. 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 Red House Architecture dated August 4,2021. 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 one and two-story wood-frame structure with an attached garage/shop located on the site as shown on Figure l. Ground floors will likely be a combination of structural over crawlspace and slab-on-grade. Cut depths are expected to range between about 2 to 5 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 subject site was vacant at the time of our field exploration. The building envelope corners were marked. The ground surface is gently sloping down to the south with about 5 feet of elevation difference across the residence footprint. Vegetation consists of grass and weeds with sagebrush. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating three exploratory pits at the approximate locations shown on Figure l. The logs of the pits are presented on Figure 2. The subsoils encountered, below about % foof of topsoil, consist of up to 4 feet of very stiff, sandy silt and clay underlain by relatively dense, basalt gravel and cobbles in a highly calcareous cemented sandy silt matrix down to the maximum excavated depth of 5 feet. Results of swell-consolidation testing performed on a relatively undisturbed sample of the silt and clay soil, presented on Figure 3, indicate low compressibility under existing low moisture conditions and light loading and a low collapse potential when wetted under constant light -2-surcharge. Results of a gradation analysis performed on a sample of sandy silt and gravel (minusS-inch fraction) obtained from the site are presented on Figure 4. No free water was observed inthe pits at the time of excar¡ation anclthe soils uzere slightl), moist.Foundation Bearing Conditions: The upper silt and clay soils encountered in the pits possess alow bearing capacity ancl low to mocierate settlement potential when wettecl uncler load. 'l'heunderlying basalt gravel and cobble soils possess a moderate bearing capacity and typically lowsettlement potential when rvetted.Foundation Recommendations: Considering the subsoil conditions encountered in theexploratory pits and the nature of the proposed construction, we recommend spread footingsplaced on the undisturbed natural soils designed for an allowable bearing pressure of 1,500 psffor support of the proposed residence. The topsoil should be removed from below building areas.Footings that bear entirely on the underlying silt and basalt rock soils can be designed for anallorvable bearing pressure of 2,500 psf. We should observe the completed building excavationfor bearing conditions prior to forming footings. Our experience in this area indicates that thebasalt rock soil can be excavated a few feet with a heavy-duty trackhoe but rock excavationtechniques could also be needed such as for deeper cuts and trenches. Footings should be aminimum witith of 18 inches lor oontinuous walls anú2leeL for columns. Topsoil antJ loosedisturbed soils encountered at the foundation bearing level within the excavation should heremoved and the footing bearing level extended down to the undisturbed natural soils. Voidscreated from boulder removal at footing grade should be backfilled with concrete or a structuralmaterial such as road base compacted to at least 98 percent of standard Proctor density at amoisture content near optimum. Exterior footings should be provided with adequate cover abovetheir bearing elevations for frost protection. Placement of footings at least 36 inches below theexterior grade is typically used in this area. Continuous foundation walls should be reinforcedtop and bottom to span localanomalies such as by assuming an unsupported length of at leastl2 feet. Foundation walls acting as retaining structures should be designed to resist a lateralearth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil asbuokfill excluding orgunios und rock lurger thun 6 inshes or imporl.ed grunulur mul.eriul such usroad base.Floor Slabs: The natural on-site soils, exchrsive of topsoil, can be usecl to support lightly loacleclslab-on-grade construction with a risk of movement if placed on the upper silt and clay soils.The subgrade should be evaluated for slab support and possible need for structural fill such asroad base at the time of excavation. To reduce the effects of some differentialmovement, floorslabs should be separated frorn allbearing walls and columns with expansion joints which allowunrestrained vertical movement. Floor slab controljoints should be used to reduce damage dueto shrinkage cracking. The requirements for joint spacing and slab reinforcement should beestablished by the designer based on experience and the intended slab use. A minimum 4-inchlayer of free-draining gravel should be placed beneath basement level slabs (if any) to facilitatedrainage. This material should consist of minus 2-inch aggregate with less than 50% passing theNo. 4 sicvc and lcss than 2o/o passing thc No. 200 sicvc.Kumar & Associates, lnc. @Project No. 21-7-660 -3- All fill materials for support of floor slabs should be compacted to at \east95Yo 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 or imported road base. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the areathat 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, crawlspace and basement areas (if any), be protected from wetting and hydrostatic pressure buildup by an underdrain system. The drains should consist ofldrainpipe placed in the bottom of the wall backfill surrounded above the invert levelwith free-draining granular material. The drain should be placed ateach level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum lo/oto a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2%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 backftll should be at least lYz feet deep Surface Drainage: Proper surface grading and drainage will be critical to help limit wetting of the bearing soils. 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% 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 sr¡rface surrounding the exterior of the building shoulcl he slopecl to drain away from the foundation in all directions. We recommend a minimum slope of 12 inches in the fìrst l0 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in pavernent and walkway areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfrll. 5) Landscaping which requires regular heavy irrigation should be located at least 5 feet from the building. Limitations: This study has been conducted in accordance with generally accepted geotechnical engineering principlcs and practiccs in this arca at this timc. Wc makc no warranty cithcr 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 proposcd typc of construction, and our experience in the area. Our services do not include determining the presence, prevention or possibility of rnold Kumar & Associates, lnc, @ Project No, 21-7-660 -4-or other biological contaminants (MOBC) developing in the fufure. If the client is concernedabout MOBC, then a professional in this special fìeld of practice should be consulted. Ourfindings include intorpolation and extrapolotion of thc subsurface conditions idsntified at theexploratory pits and variations in the subsurface conditions may not become evident untilexcavation is perfcrrmed, If conclitions encountered during construction appear different fromthose described in this report, we should be notified at once so re-evaluation of thereoorrunendations nay be made.This report has been prepared for the exclusive use by our client for design purposes. We are notresponsible for technical interpretations by others of ow information. As the project evolves, weshould provide continued consultation and field services during construction to review andmonitor the implementation of our recommendations, and to verily that the recommendationshave been appropriately interpreted. Significant design changes may require additional analysisor modifications to the recommendations presented herein. We recommend on-site observationof excavations and foundation bearing strata and testing of structural fill by a representative ofthe geotechnical engineer.If you have any questions or if we may be of further assistance, please let us know.Respectfu lly Submitted,å{i'g¡a¡:er {-{¿ "Às;sceintes, Ene"Steven L. Pawlak, P.E.ReviewedDarúel E. Hardin, P.E.SLPlkacAttachments: Figure I - Location of Exploratory PitsFigure 2 - Logs of Exploratory PitsFigure 3 - Swell-Consolidation Test ResultsFigure 4 - Gradation Test ResultsTable I - Summary of Laboratory Test Resultsb152226Kurnar &,Associates, incFroJect Nn. t'|"7"66{l IJJ u CI_ oãv.i @c C'zv t\0 APPROXIMATE SCALE-FEET 21 -7 -660 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1 ¡IÊfiI1lbIFig. 2LOGS OF EXPLORATORY PITSKumar & Associates21 -7 -660PIT IEL. 6gss'Pll 2EL. 6935'PIT 3EL. 6927'0UFl¡Jl¡JtLI-Fo_Lrlô-JWÇ=6.9DD= 1 02|-l.¡ll¿lLI-t--o-ulô- WC=10.1' -zoo=71-, {-4=24--l -2oo=J8I-lI_5ÃLEGENDTOPSO|L; ORGANIC SANDY SILT AND CLAY, FIRM, BROWNCLAY AND SILT (CL-ML); SANDY, STIFF, SLIGHTLY MOIST, LIGHT BROWNAND CALCAREOUS.SLIGHT POROUSBASALT GRAVEL, COBBLES AND SILT (GM-ML); HIGHLY CALCAREOUS SANDY SILT wlTHBASALT ROCK, VERY HARD, SLIGHTLY MOIST, GRAY AND WHITE.FtHAND DRIVEN 2-INCH DIAMETER LINER SAMPLE.DISTURBED BULK SAMPLE.IPRACTICAL DIGGING REFUSAL.NOTES1. THE EXPLORATORY PITS WERE EXCAVATED WITH A MINI-EXCAVATOR ON SEPTEMBER 20, 2021.2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROMFEATURES SHOWN ON THE SITE PLAN PROVIDED.3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEENCONTOURS ON THE SITE PLAN PROVIDED.4, THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLYTO THE DEGREE IMPLIED BY THE METHOD USED.5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THEAPPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.6. GROUNDWATER WAS NOT ENCOUNTERED IN TI.IE PITS AT THE TIME OF EXCAVATION. PITS WEREBACKFILLED SUBSEQUENT TO SAMPLING.7. LABORATORY TEST RESULTS:WC = WATER CONTENT (%) (ASTM D 2216);DD = DRY DENSITY (PCt) (ISTV D 2216):+4 = PERCENTAGE RETAINED 0N No. 4 SIEVE (ASTM D a22);_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140). I SAMPLE 0F: Sondy Silt ond Cloy FROM: Pit 2 @ 1.5' WC = 6.9 %, DD = 102 pcl frå b6 i¡ tho w¡ltt€n*ìthoul of ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 1 0ñ JJ -l UJ =v1 t-2 zotr ô_< JoU'z.oor -4 -5 1.0 APPLIED PRESSURE - KSF 10 100 21 -7 -660 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig.3 IçhFig. 4GRADATION TEST RESULTSKumar & Associates21 -7 -660'I1I-- -t-'tJOPENINCS- ,.1?.IlSIEVE ANALYSISHYDROMETER ANALYSIS=ãPt00g0ao70605010s020to0.--, ,t.olo2050&5080708090?EãË¡L il..r.t I4.75I- 1 roo200I.00t.oo2.oo5.1502.0IN MILLIMETERSI52DIAMETER OFCLAY TO SILÏCOBBLESGRAVEL 21 %LIQUID LIMITSAND 38 %PLASTICITY INDEXSILT AND CLAY 38 %SAMPLE OF: Colcoreous Sondy Slll ond GrovelFROM:PIt1O4'-5'Th.rt hrl r[ull¡ qpply only io lht:omplor vhlch war€ ,ertad. Thrl.¡llng rcÞorl tholl not b. r.producrd,.xoopl ln full, wllhoul lh! wrlltlnopprovol of Kumq¡ & A!!oclolo!, lnc.sl.vr qnrlylh l.lllno h oorform.d lnoocordoncå wllh ASÍM 06913, ASTM 07928,ASIM C136 ondlor A51M Dll,l0.COARSEFINEMEDTUM lCOlnSeFINEGRAVELSAND lcnlfumar & Associates, lnc.@Geotechnical and Materials Engineersand Environmental ScientistsTABLE 1SUMMARY OF LABORATORY TEST RESULTSNo. 21-7-66021IY,4-52%-36.9I0.I102SAMPLE LOCATIONPITDEPTHNATURALMOISTURECONTENTNATURALDRYDENS]TY24383871PERCENTPASSING NO.200 stEVEGRADATIONGRAVEL%tSAND(:/"1(o/olLIQUID LIMITPLASTICINDËX(%lATTERBERG LIMITSlosf)UNCONFINEDCOMPRESSIVESTRENGTHSOIL TYPESandy Silt and ClaySandy Silt and ClayCalcareous Sandy Silt andGravel