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Home My WebLink AboutSubsoil Study Report 10.13.2016H.P*I(UMAR 5020 County Road 154 Glenwood Springs, CO 81601 Phone: (970) 945-7988 Fax (970) 945-8454 Email: hpkglenwood @ kumarusa.com Geotechnical Errgirreering ! Engìn*ering Geology fulaterials Testing | Ënvironmental Office Locations: Parker, Glenwood Spríngs, and Silverthorne, Colorado October 13,2AL6 Rob Classen P.O.Box 1227 Glenwood Springs, Colorado 81602 (dr:awbd@rrof.net) Project No.16-7-473 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot2, Filing l, Elk Springs, Elk Springs Drive' Garfield County, Colorado Dear Mr. Classen: As requested, H-P/Kumar 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 io you dated September 23,2016. 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 story wood frame construction above a walkout hasement and crawlspace area with an attached garage. The residence will be located on the site as shown on Figure 1. Basement and garàge floors will be slab-on-grade' Cut depths are expected to range between about 3 to 10 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, wJshould be notified to re-evaluate the recommendations presented in this report. Site Conditions: The site is vacant and vegetated with a pinion and juniper forest with scattered sage brush, grass and weeds. The site is located on the rim of an upland rolling mesa above the RJaring Foik River Valley. The ground surface in the building area slopes down to the northwest and west at moãerate tı slight grades. A very steep hillside with basalt scree is located west of the buildin g afea about 30 feet. Eagle Valley Evaporite is exposed in roadway cuts along the county road below the site. subsidence potential: Bedrock of the Pennsylvanian Age Eagle valley Evaporite likely underlies the project site. These rocks are a sequence of gypsiferious shale, fine-grained sandstone/siltstone and limestone with some massive beds of gypsum. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the a property. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, several broad subsidence areas and sinkholes have been observecl. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork River Valley. No evidence of subsidence or sinkholes was observed on the property or encountered in the subsurface materials, however, the exploratory pits were relatively shallow, for foundation design only. Based on our present knowledge of the subsurface conditions at the site, it can not be said for certain that sinkholes will not develop. The risk of future ground subsidence at the site throughout the service life of the structure, in our opinion is low, however the owner should be aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. 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 were variable and below about one foot of topsoil, consisted of calcareous basalt cobbles and boulders in a sandy silty clay matrix at the uphill pit and 18 inches of sandy silty clay overlying sandy silt and gravel with scattered cobbles in the downhill pit. Results of swell-consolidation testing performed on relatively undisturbed samples of sandy silt with gravel, presented on Figures 4 and 5, indicate low compressibility under existing moisture and light loading and moderate compression when wetted under additional loading. 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 condltions 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 soil bearing pressure of 1,500 psf for support of the proposed residence. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. Utility trenches and deep cut areas below about 3 feet at the upper part of the residence may require rock excavating techniques such as chipping or blasting. 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 soils. Voids created from boulder removal at footing grade should be filled with a structural material such as road base compacted to at least 98Vo standard Proctor density at a moisture content near optimum or with concrete. 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 50 pcf for the on-site soil as backfill, excluding rock larger than about 6 inches' 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 uscd to reducc damagc duc H-P \ KUMAR Project No. 16-7-473 -3- to shrinkage cracking. The requirements for joint spacing ancl slab reinfcrrcement 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 slabs to facilitate drainage. This material should consist of minus 2inch aggregate with less than 5O7o passing the No. 4 sieve and less thanT%o passing the No. 200 sieve. 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, crawlspace and basement 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 I foot below lowest adjacent finish grade and sloped at a minimum l7o to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2Vo 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 IVz 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. ,Z) 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 90Vo of the maximum standard Proctor density in landscape areas. Free-draining wall backfill should be capped with at least 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 12 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. 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 10 feet fiom the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the foundation caused by irrigation. 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 waffanty either "^ir.r, orimplied. The conclusions and recommendations submitted in this report are based upän the data obtained from the exploratory pits excavated at the locations indicated on Figure 1 un¿ to the depths shown on Figure 2, the proposed type of construction, and our experience in the area. Oui services do not include determining the presence, prevention or possibility of mold H-P \ KUMAR Project No. 16-7-473 -4- 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 pu{poses. '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 verify 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, l-l-P+ s E. Eller Reviewed by: Steven L. Pawlak, LEE/ksw attachments Figure I -oratory Pits Figure 2 -Logs of Exploratory Pits Figure 3 - Legend and Notes Figures 4 8. 5 - Swell-Consolidation Test Results Table I - Summary of Laboratory Test Results H-P \ KUMAR Project No. 16-7-473 ¡t * -.â.ç'ı Ld2 La3A¡nip Ferxh SrÈdM¡¡onFSDgt{ol I a- ,r r t , , {,*sF'lçãtrb €¿ J..*'rß, b lÐrd:J ,) ß: 't n'' I r'e* ÊqIIII t II II II e',tI Ç. I I I I I I l I Pll 2 {}" PIT 1 € 3I// Sur 4!(-91.û.!!!i.ç!4!! dt l. 3t 2¡ Fí9. 1LOCATION OF EXPLORATORY PITSH.P\KUMAR fi,Lf.v.,.l,.r l.,l.r L¡ .,t; F,Xrr..r.:i,'j ì1,,r/i lr.ilpr:Jb lrI: ¡Q ì i::,7r;or)r)!rr'i¡' 16-7 -473 NOT TO SCALE PIT 1 EL. 6786' PIT 2 EL. 6778' o0 55 WC=f 0.7 DD=60 -200=68 WC=13.1 0D=7 1 WÇ=12.4 DD=76 Ft¡J l¡J 14 I¡t-o- l¿¡ô t- UJ l¡JIt I-l-o-l¡lÕ 't0 15 10 t5 ? Fis. 2LOGS OF EXPLORATORY PIÏS16-7 -473 H.P*KUMAR í¡ rÙ.i:rr!..,.t i: ilrì!r.rf - ; I rrrlrril-r.ì ;îr:i-¿l' Mrk..L,¡r- :/rìlrrlj I 'rr¡r::ir!:!Í t: LEGEND N TQPSOIL; ORGANIC SANDY SILT WITH COBBLES AND BOULDERS, SOFT, SLIGHTLY MOIST, DARK BROWN. GRAVEL ANo CLAY (GM-CL); SANDY, SILTY, CoBBLES AND BOULDERS, MEDIUM DENSE, MOIST, LIGHT BROWN, CALCAREOUS. CLAY (cL); SANDY, SILTY, STIFF, MOIST, BROWN. GRAVEL (GM); LIGI.IT BROWN BASALT COBBLES IN A SANDY SILT MATRIX, MEDIUM DENSE, SLIGHTLY MOIST, , CALCAREOUS. HAND DRIVEN LINER SAMPLE DISTURBED BULK SAMPLE, PRACTICAL DIGGING REFUSAL. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A MINI-EXCAVATOR ON OCTOBER 3,2016. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3, 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 8Y THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SI.{OWN ON THE EXPLORATORY PIT LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE ÏRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATING. 7, LABORATORY TEST RESULTS: wc = wATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); -ZOQ = PERCENTAGE PASSING NO' 200 SIEVE (ASTM D 1 1 40). F I I E I E i Fis. 3LEGEND AND NOTES16-7 -473 H-P\KUMAR l Ìtü,¡D{lrI it:()t4v(iro¡ca\rrLJi tj,qn4e,itliJ ñlrþhl, IÐ$l!rï¡ : irt?ifi )rrì 0 ^-2N j-s ¡¡J =tt1 t-4 z.9F OE Jothzo<r_6 -1 -7 -9 -8 6 3 3 SAMPLE OF: Sondy Silt wlfh Grovel FROM:Pit2g.5' WC = 13.1 %, DD = 71 pcf _i_-''i' r' ,j ,t' ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING ln Fig. 4SWELL-CONSOLIDATION TEST RESULTH-P\KUMAR {j{ric.jni,.:.¡i':r:Qìrie¡--r'q !ttglr}\¡nrt! -l{rjilg? inr'!¡,a!': IÞ.rx¡Ì,i, fj,!,r, )nilì!i!rl:ri 16-7-473 - KSF t00 SAMPLE OF: Sondy Sílt wllh GrovEl FROM:Boring 2@7' WC = 12,4%, DD = 76 pcf b.d ¡nD-#€,¡¡tl --..--; -.,.-.,--.-.,,-1- ;' i,l- -- -' -ì -- -:.1:) ; i'l ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 0 -1 -2 -5 -4 -5 -6 N JJt¡l =(n z.oË ô Jotnzo(J t 3 E I t.0 SWILL-CONSOLIDATION TESÏ RTSULT Fig. 516-7-473 H-P=KUMAR l:er*fñn'âti årì.¡ì'rêir{ì!ì !¡ajrnÐ,ril:¿1 : j*r:lrqt i4r!È¡.i.; IËclr$ ì f:il!'r'rùrirllnal H-P*I{UMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. 16-7-473UNCONFINEDCOMPRESSIVESTRENGTHSOIL TYPESandy Silt with GravelSandy Silt with GravelSandy Silt with GravelATTERBERG LIMITSPLASTICINDEX(%lLIQUID LIMIT(%l8068PERCENTPASSING NO200 stEVEGRADATIONSAND(%)GRAVEL(/'lNATURALDRY DENSITYlocf)7176NATURALMOISTURECONTENTt%lto.7IJ1t2.4SAMPLE LOCATIONDEPTH(ft)J57PIT2