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Home My WebLink AboutSubsoils Report for FoundationlGrfffiïiffiFå'*" An Employao Orynsd Compony 5020 County Road 15'4i Gler¡wood Springs, CO 8l60ill phone: (970) 945-7984 fax: (970) 945-843:4 ernaill: lkaglenwood@kumarusa-corm www.kumarusa.com Offiaellocations: Denver (Í{Q)i Farike4 Coloradkr Springs, Fort Colllins, Glbnwood Sprrirngs, andlSurmit County, Coloradbr May 17,2O22 Richard Harbus 201 Commons Park South Stamford, Connecticut 06902 .com Project No.22-7-21,0 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 86, Filing 7, Elk Springs, 56 Gossamer Road, Garfield County, Colorado Dear Richard: 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 March2,2022. 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 wood-frame structure with attached garage located between the exploratory pits as shown on Figure 1. Ground floor could be slab- on-grade or structural over crawlspace. 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 ground surface slopes down to the south at a grade of about 10 percent through the building site then about25 percent further down to the southeast. Vegetation consists of sagebrush, grass and weeds in the proposed building area with juniper on the steeper slope. Basalt cobbles and boulders were visible at the surface of the building area. 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 presented on Figure 2. The subsoils encountered, below about I to IYz feet of topsoil, consist of dense, basalt, gravel, cobbles and boulders in a highly calcareous sandy silt matrix down to the maximum explored depth of 3 feet. Excavating in the dense cobbles and boulders was difhcult ", and practical refusal was encountered in the deposit. Results of a gradation analysis perfbnned on a sample of silty sandy 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 2,500 psf for support of the proposed residence. The matrix soils could tend to compress after wetting with expected minor post-construction foundation settlement. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Topsoil and loose 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 granular soils. Difficult excavation conditions could be encountered at the site due to the cobbles and boulders in the cemented matrix. Foundation excavations will probably require alarge excavator and/or chipping equipment. Exterior footings should be provided with adequate cover above their bearing elevations for frost 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 organics and rock larger than 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 eflbcts of some ditÏerential 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 relatively well graded sand and gravel such as matl base should be plaued beneath the garage slab for support. 'l'his material should consist of minus Z-inch aggregate with less than 50% passing the No. 4 sieve and less thanZo/opassing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least95%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. Ku¡nar & As¡ocides" lne. @ Proiectilo. 2?.3-210 -J- 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. For slab-on-grade or shallow crawlspace construction where the finish floor grade is at or above surrounding grade an underdrain system is not required. We recommend below- grade constructiono such as retaining walls and deeper crawlspace areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. Where used, 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 l%oto a suitable gravity outlet or sump and pump. Free-draining granular material used in the underdrain system should contain less than 2o/opassing the 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 lYz feet deep and covered with filter fabric such as Mirafi l40N 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 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. Free-draining wall backfill should be covered with filter fabric and capped with about2 feet of the on-site, hner 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 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. 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. Kumar & Associales, lnc. @ Froþct l{o' 22--Í-24ü -4- I"inimin¡: This study has bem mdr¡ded in aæordmæ wih gßnÊraily aooEÉsd gwtofti¡cal Gnginffiiqg trifüplcs and þactiæ in lftis ilüa d -' :s time, l#e make no wmmty eifrer qress or iryliolt The conclusirm md rmcnddirms s¡hiüsd in ti$ rEput acbasod qmúe dúfuined from the @trdmypib excandod dtro locdions indicdodon Figue f md to ftG dcptrs ehov,'n on Figrne I lhe pqoood type of mstruøion, d on qleriæ in treaea Oussrris do not inctudedetemininglhep¡esenæ"pudimmpoesibillityofmold ø otrerbiological onta¡ninants ([[OBC) dslrtilqlû4g in üG fure. IfftG rri€d is msnd úoü trláOBC, "'- a professional in ltis ryGúl fidd ofpacfiæ should bo oons¡ltert Orn findingn inctüdo ¡úcnpolation and æAolrim of fre sbo¡råæ oonditiw ifuified at úo euqllordmypits d vmiations infre submrñoe ditims may notbome Gvidcrt until excardim is performed. If conditirrrs enomusd ùriag msftudim rycr ditrrrrm frm ftoæ desøibed in ftis rqnrt, we úmld be difrod at moo so rçer¿ah¡dim oflùe rmaddionsmay be made. fhis rcput has bm prepared forfre exch¡sir¿e re by un dient fu design prpm- üre ae not rcryonsibl€ fitr tffiical interprffiirm by fu ofou infudim- l\s úe projoct ermlves, we úould povi& offiinued consr¡lMm md frdd sr¿im dudng CIomffi¡dion to rsr¿iew md mgriüm frc ftn[lematation of owrmr¡menddicrc" æd b \¿€riry thx üe rmendatirm h¿ne b€Gn rypoerldety interprebd. signifrcaú d€sign drrqgcs may roqnire adûTimd m¿lyrús ømodiñcdim to fte recommaddisrs pesøod hcrein V/c romd orsiþ oñeerndim of excarødirrx md foundation bemiry ffi md t€Sing of Sr¡ch¡ral fill by a rqrestntaûive of fre gsoteúnical engineer. IfSrou harøe my questions or if rema¡rbe offfiq m¡mæ, ptease lct us know- Rcryodilty Submiüe{ Kumar & Associates, Inc. JmeslL Pusms, P Revicuredb¡n ffi**- Støvonl- Pawlalq P.E. IHPlIæ, attnr:hmcrfn Figrne I - LocatiomrrfftriludmyPits Figwe 2 - I-ogs of'E:Smdory Pits Figue 3 - Gradati¡m Thd Remlts Kumar & Associales, lnc, @ Project No. 22-T-210 s$, s0 srl e' 6" t0 dr$ è f t oi)\. ¿{il ı¿r /, ."rq, '\deso- é ¿ 10'x5-0' Util Eosem {,t { 30 0 0 APPROXIMATE SCALE-FEET LOCATION OF EXPLORATORY PITS Fig. 122-7 -210 Kumar & Associates I PIT I EL. 6939.5' PIT 2 EL. 6931.5' PIT 5 EL. 6934' o t- l¡JulL I-t-(L tdô I +4=52 -200=1 4 Ft¡JIJ LL ITt-fL LIô 5 5 LEOEND TOPSOIL; SANDY GRAVELLY SILT, ROOTS AND ORGANICS FIRM, SLIGHTLY MOIST, TAN, WITH SCAÏÏERED BASALT COBBLES. GRAVEL SILT MA (CU); g¡s¡Lr GRAVEL, COBBLES AND BOULDERS lN A HIGHLY CALCAREoUS SANDY TRIX, DENSE, SLIGHTLY MOIST, TAN. I I I I DISTURBED BULK SAMPLE PRACTICAL DIGGING REFUSAL. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MAY 6, 2022. 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 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 WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING. 7. LABORATORY TEST RESULTS:+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (¡STV O ¿ZZ); -2OO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). 22-7-210 Kumar & Associates LOGS OF EXPLORATORY PITS Fis. 2 HYDROMETER ANALYSIS SIEVE ANALYSIS U.S, STÑDARD SERIES CLEAN SOUARE OPENINGS at^. t/^n t tttartt{at TIf,E READINOS aôltN teMtx ¿vtNt4 HRS 7 HnSa¡ ltN l¡ vt¡ T 100 90 ao 70 a0 50 40 30 20 fo o o lo 20 30 & 30 60 70 ao to ro0 = OIAMETER OF IN RS CLAY TO SILT COBBLES GRAVEL 52 X SAND 31 '6 LIQUID TIMIT PLASTICITY INDEX SAMPLE OF: Highly Colcor€ous Silþ Sondy Grovel SILT AND CLAY 11 i4 FROM: Pít3O2.5'-3' thc¡c lc¡l rGsull! opply only lo lh. .omplc¡ rhlch v.r. lc¡lcd. Tha lrsllng rcporl lholl nol b. rcproduccd,.xc.pf ln full, vllhoul lh. wrlfl.ñ opprovol of Kumor & Arrociol.r, lnc. Sl.v. onolysb l.lllñg l! p.rfom.d ¡n occordqnc. ulth ASTY 069f3, ASTII D7928, ASTM C136 ond/or ASTM Dll,l0. GRAVELSAND FINE MEDIUM ICOARSE FINE COARSE 22-7-210 Kumar & Associates GRADATION TEST RESULTS Fig.3