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Home My WebLink AboutSubsoil Study for Foundation Design 09.28.2018H.PVKUMAR GeoJecñnlcal Englneering I Engineering Geology Matedals Testing I Environmental 5020 County Road 154 Glenwood Springs, C0 81601 Phone: (970) 945-7988 Fax (970) 94S-84S4 Email: hpkglenwood@kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado September 28,2018 Custom'Works Attn: Dan Dixon P.O. Box 508 Carbondale, Colorado 8t623 d@ RECEIVED I)EC 0 0 20tS GARFIELD COUNTY COMMUNITY DEVELOPMENT Project No. 18-7-561 Subject:subsoil study for Foundation Design, Proposed Residence, 2935 Highw ay 133, Carbondale, Garfield County, Colorado Gentlemen: As requested, H-PlKumar 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 September I l, 2018. 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 garage at the ground level located on the site as shown on Figure 1. Ground floor is proposed to be 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. lf 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: There is cunently a one-story wood-frame structure at the subject site to the east of the proposed residence. Topography at the site is valley bottom with slopes less than 5 percent grade. Vegetation consists of landscaped trees, shrubs, and lawn. The Carbondale Town ditch flows along the western edge of the lot. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two cxploratory pits at the apploxiutatc luuatiuls shuwn on Figure 1. The logs of the pits are a presented on Figure 2. The subsoils encountered, below about lVzfeet of topsoil, consist of about ZYz to 3 feet of sandy clay overlying silty sandy gravel with cobblcs and boulders down to the maximum depth explored of 5 feet in Pit 1 and 6 feet in Pit 2. Results of swell-consolidation testing performed on relatively undisturbed samples of the upper sandy clay material, presented on Figures 3 and 4, indicate moderate compressibility under existing moisture conditions and light loading and a low collapse potential when wetted. Results of a gradation analysis performed on a sample of silty sandy gravel (minus 3-inch fraction) obtained from pit 2 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 Bearing Conditions: Spread footings appear feasible for foundation support of the building' The upper fine-grained soils at the site possess low bearing capacity and, in general, moderate settlement potential, especially when wetted under load. We recommend that the upper fine-grained soils be removed in proposed footing areas and either the foundation bearing level be extended down to the relatively dense natural granular soils or structural fill be placed on the exposed natural granular soils to re-establish design footing grade. Structural fill should consist of an imported granular material meeting either CDOT Class 2 or Class 6 specifications, be placed in 6-inch thick lifts, and compacted to at least 98 percent standard proctor density at a moisture content within 2 percent of optimum. Provided below are recoïlmendations for spread footings bearing on the natural granular soils or compacted structural fill. It should be feasible to bear the floor slab on the upper fine-grained soils with some risk of settlement and distress. We should observe the completed foundation excavation to deterrnine the granular soils have been exposed, and placement and compaction of structural fill to design bearing level. Foundation Recommendations: Considering the subsoit conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings bearing entirely on the relatively dense, natural granular soils or on compacted structural fill be designed for an allowable soil bearing pressllre of 2,500 psf for support of the proposcd residence' Post-construction foundation settlement should be relatively minor. Footings should be a minimum width of 16 inches for continuous walls and2 feeffor columns. The upper fine- H-PNKUMAR Project No. 18-7-561 -3- Srained soils and loose and disturbed soils encountered at the foundation bearing level within the excavation should be removecl ancl the footing bearing level extended down to the undisturbed natural granular soils or design footing grade re-established with compacted structural fill. 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 l0 feet. Foundation walls acting as retaining structures (if any) 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 fine-grained soil as backfill. Floor Slabs: The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade construction with some risk of settlement and distress. 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 relatively well-graded sand and gravel such as road base should be placed beneath interior slabs for support. This material should consist of minus 2-inch aggregate with less tban 5AVo passing the No. 4 sieve and less than lTVo passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95Vo of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site soils devoid ofvegetation, topsoil and oversized rock. 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 90Vo of the maximum standard Proctor density in landscape areas. H.P*KUIVIAR Project No. 18-7.561 -4- 3) 4) Free-draining wall backfili should be capped with ahont 2 feet of the on-sire, finer graded soils to ¡educe su¡face water infiltration. The ground surface sumounding the exterior of the buitding should be sloped to drain away from the foundation in all directions. we recommend a minimum slope of 6 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. Roof downspouts and drains should discharge well beyond the limits of all backfill. Landscaping which reqttires regular heavy inigation should bc located at least 5 feet from the building. s) Limitations; This study has been conducted in acco¡dance with generally accepted geotechnical engineering principles and praclices in this area at this time. We make no warrånty 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 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 identifieci 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 recommondations may bc madc. This report has been prepared for the exclusive urse by our client for design purposes. we are not responsible fo¡ technical interpretations by others of our information. As the project evolves, we should provide conlinued consultation and field services during construction to review and monitor the impicmcntation of our t'ecurnrnendå.Tions, and to verify that the recommendations havc been appropriately interpreted. signiticant design changes may require additional analysis or modifications to the recttmmendations presented herein. we recommend on-site observation H-P*t<Ulr¡¡R Project No. 18-7-561 5 ofexcavations 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, H-P+KUMAR l/k/tú\0-- Robert L. Duran, E. I. Reviewed by: Steven L. Pawlak, RLD/kac attachments Figure I -Pits Figure 2 - Logs of Exploratory Pits Figures 3 and 4 - Swell-Consolidation Test Results Figure 5 - Gradation Test Results Table 1 - Summary of Laboratory Test Results 2?2 H-PV¡(IJMAR Project No. 18-7-561 Þù Bldg 27.5' Nûthedy Roundøry L¡4ê øf Lôt lâ ' Rac. S 8744A' w 16s.oo' +/- a (¡) () PIT 1 t x _) I þilch (t u1 L.l N .<)i:jc) uúld s aruf'o' f 166,¿0' +/- ,.7 Existing Ðrive w0 New ÐrivewoY P'T 2 - -!2. a E r sa fxistinq Blds Corbondo¡e lora Ðitch 14,166 sq.ft 0.33 ocres 28.1 t\.a lv 8t'll'6A- e Rec.s 8744'O' '{ 165'00'+/- APPROXIMATE SCALE*FEET '18-7-561 H-PVKUMAR LOCATION OF EXPLORATORY PITS Fig. 1 1' PIT 1 EL. 1 00'PIT 2tL. I 00' U rr FldLIr! I-t--o-tdâ WC=9.7 -, DD--92 -i WC= 1 6.0 DD=101 -\ WC=4.2 +4=43 -200=30 F- L¡Jt!f! ITl-ô- l¡J ff q 10 LEGEND R 10 TOPSOIL; SANDY SILT AND CLAY wtTH ORGAN|CS. cLAy (cL), SANDY, StLTy, SI|FF, SLtcHTLy MO|ST, BROWN, LOW pLÀsTtctTy GRAVÊL AND COBÊLES (GM_SM), SANDY TO VERY SANDY, SILTY, MEDIUM DENSE, SLIGHTLYMOISï, BROWN. HAND DRIVEN 2_INCH ÐIAMETER LINER SAMPLE. DISTURBED BULK SAMPLE I PRACTICAL DIGGING REFUSAL. NOTES F I 1 2 THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON SEPTEMBER 14,2018. THÊ LOCATIONS OF IHE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACINO FROMFEATURES SHOWN ON THE SITE PLAN PROVIDED. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINEO BY HAND LEVEL AND REFER TOPIT 1 AS ELEVATION 1OO" ASSUMED. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLYTO THE DËGREE IMPLIED BY THE MËTHOD USEO. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THEAPPROXIMATE EouNDARIEs BETwEEN MATERTAL TypEs AND THt rRANstloNs MAy ee CnAoul¡_. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WEREBACKFILLED SUBSEQUTNT TO SAMPLINC LÀBORATORY TEST RESULTS: WC = WATER CONTENT (Z) (ASTM T 2216); DD = DRY DEñslTY (pct) (lsru Ð 2Zt6);+4 = pERCENTAGE RETATNED 0N NO. 4 STEVE (ASTU O +ZZ);_2OQ = PERCENTAGE PASSING NO. 2OO SIEVE (ASTM O I14b) ? 4. 5. 6. 7. o' 1 8-7-561 H.PVKUMAR LOGS OF EXPLORATORY PITS lig. 2 ¡ SAMPLE OF: Sondy Cloy FROM:PitlOS' WC = 9.7 %, DD = 92 pcf 0 -t JJl¿l3ah I zIf- â JoU,zo(J -¿ 3 4 5 6 -7 -8 -o t.0 tfit it ol 1 L I I I ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING r 8-7-56'l H.PVKUMAR SWELL-CONSOLIDATION TEST RTSULTS Fig. 3 SAMPTE OF: Sondy Cloy FROM:Pit2ç^3' WC = 16.0 %, DD = 101 pcf òa lsll, ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 1 JJ l¡J3an I zo t- Õ JoØzo(J 0 1 2 3 4 _R -6 1.0 APPLIED PRÉSSURE - KSF r00 1 8-7-561 H-PVKUMAR SWTLL_CONSOLIDATION TEST RISULTS Fig. 4 HYOROMEIER ANALYS¡S SIEVE ANÂLYSIS fm 7 HPS 2 r ro0 90 t0 ,o to 30 ao to 20 ro o ro 20 30 ¡o 50 ao 70 to 90 1@ r E a! I r i it I,a2t OIAMEÍER OF CLAY TO SILT SAND GOSBLES GRÀVSL 13 N SAND 27 " LIQU¡Ð TIMIT PLASTICITY INOEX SAMFTE OF: Sllly Sondy Grovel SILT ANÐ CLAY 30 X FROM:Pit2O5-5,5' Thr¡s l¡¡l r.lulll opFly oñly to lh.tompl.. rhlch r¡r¡ l¡ftd. fh¡tcrling ruporl.holt nol b. raprcduc.d,.rc.Þl ln full, rlthout lh. rrÌtt.noppdol of Kumor t Atrælolat. l¡c.Sltvc o¡olyrb la.tlng lr p.rlormad ln occordoñcr rlth ASft¡ û422. Asfit Cl56snd/o/ ^SlM Dlt.to. I ¡ I I I I ¡ -¿¿ I I--t .l T GRAVEL FINE MEgIUM FINE COARSE 1 8-7-561 H-PVKUMAR GRADATION TTST RESULTS Fig. 5 H.PTKUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. l8-7-561SOILTYPESandy ClaySandy ClaySilty Sandy GravelUNCONFINEDCOMPRESSIVESTRENGTI{(psf)ATTERBERG Lll'lllTSPLASTICINDEX(o/"1LIQUIDLIMIT(o/olPERCENTPASSINGNO.200SIEVE30NATURALDRYDENSITYGRAVELSAND$t(%)274392101NATURALMOISTURECONTENT(o/"19.716.04.2SAMPLE LOCATIONDEPTH(fr)aJJ5-5V2PIT1)