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Home My WebLink AboutSubsoil Study for Foundation 04.26.19t$rt Xsnw& åscos¡sk,hc. G60tscñnical and ñlaterials fngineen aRd Envirsnmental Seientisb email An Em$oyes Oürned Compsny 502CI County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 kaglenwood@kumarusa.com wWW.kgüarusa.qofl Office Locations: tenver (l"lQ), Parker, Çolorado $prings, Fort Collins, Glenwood Springs, and Sumrnit County, Colorado SUBSOIL STUDY FOR F'OUNDATION DESIGN PROPOSED RESIDENCE LOT 66, FILING 2, PINYON MESA PINYON MESA DRIVE GARFTELD COUNTY, COLORADO PROJECT NO. 19-7-221 APRrL 26,2019 PREPARED FOR: PMGC2, LLC ATTN: RON NORMAN 6300 RIGLEA PLACE, SUITE 900 FORT WORTTI, TEXAS 76116 rrqgr mån fr¿i s bcglobal. net TABLE OF'CONTENTS PURPOSE AND SCOPE OF STUDY I 1 -J- PROPOSED CONSTRUCTION SITE CONDITIONS ..,........... 1 - SUBSURFACE CONDITIONS....-) - FOUNDATION BEARING CONDITIONS..... DESIGN RECOMMENDATIONS................ FOUNDATIONS........ FLOOR SLABS UNDERDRAIN SYSTEM.,............ SURFACE DRAINAGE .............,. LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING FIGURES 3 and 4 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS -3- -J- 4- .-5- .-5- .-6- Kumar & Associates, lnc.Project No. 19"?-221 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot ó6, Filing 2, Pinyon Mesa, Pinyon Mesa Drive, Garfield County, Colorado. The project site is shown on Figure 1. The pu{pose of the study was to develop recommendations for foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to PMGC2,LLC, dated April 8, 2019. A field exploration program consisting of an exploratory boring was conducted to obtain information on subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classification, compressibility or swell and other engineering characteristics. The results of the field exploration and laboratory testing were analyzed to develop recoûrmendations for foundation types, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conclusions, design recolffnendations and other geotechnical engineering considerations basecl on the proposed construction and the subsoil conditions encountered. PROPOSED CONSTRUCTION The proposed residence will be two story wood frame construction above crawlspace with a slab- on-glade attached garcgo Basement or below gratle levels are not currently planned. Grading fnr the structure is assumed to be relatively minor with cut depths between 2 to 3 feet. We assume relatively light foundation loading, typical of the proposed type of construction. If building loadings, location or grading plans are signi{icantly different from those described above, we should be notified to re-evaluate the recommendations contained in this report, SITE CONDITIONS The property was vacant at the time of our exploration. The boring was drilled approximately in the middle of the building area. The site is vegetated with grass and weeds and scattered K¿lmar & Associates, lnc"Project No. 19-7-221 -2- sagebrush. The grorurd surfar"re is relatively Ilat with a geltlc slupe down l.o úre norl,h. A naturul dry drainage is located hetwccn Pajnthn¡sh Drive to the northeast and Pinyon Mesa Drive. FIELD EXPLORATION The field exploration for the project was conducted on April 17, 2019. One exploratoryboring was drilled at the location shown on Figure I to evaluate the subsurface conditions. The boring was advanced with a 4-inch diameter continuous flight auger powered by a truck-mounted CME- 458 drill rig. The boring was logged by a representative of Kumar & Associates. Samples of the subsoils were taken with 1%-inch and 2-inch I.D. spoon samplcrs. The samplers were driven into the subsoils at various depths with blows from a 140-pound hammer falling 30 inches. This test is similar to the standard penetration test described by ASTM Method D-1586. The penetration resistance values are an indication of the relative density or consistency of the subsoils. Depths at which the samples were taken and the penetration resistance values are shown on the Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The subsoils consist approximately 6-inches of topsoil, underlain by stiff to very stiff, sandy clay and silt down to l0 feet, underlain by sandy clay from l0 to 24 feet, underlain by dense, silty, clayey, gravcl and sand from 24 to 26 feet, and underlain by very stiff sandy clay to the bottom of the boring at 31 feet. The soils encountered in the boring are variable and generally similar to the soils encountered at other nearby lots. Laboratory testing performed on samples obtained during the field exploration included natural moisture content and density, and percent fines (percent passing the No. 200 sieve). Swell- consolidation testing was performed on relatively undisturbed drive samples of the silt and clay subsoils. Thc swell-consolidation test results, presented on Figures 3 and 4, indicate low compressibility under relativcly light surcharge loading. The sample of sandy clay from t5 feet showed a low expansion potential when wetted under a constant light surcharge. The laboratory testing is summarized in Table 1. Kumar & Associates, lnc.Project No. 19.7.221 -3- No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The sandy silt and clay soils encountered at expected shallow cut depth tend to settle when they become wetted. A shallow foundation placed on the sandy silt and clay soils will have a high risk of settlement if the subsoils become wetted. It will be critical to the long-term performance of the structure that the recommendations for surface grading and drainage contained in this report be followed to limit potential wetting of the bearing soils. The amount of settlement, if the bearing soils become wot, will mainly be related to the depth and extent of subsurface wetting. Settlement in the event of subsurface wetting could be I to 2 inches and likely cause building distress. Mitigation methods such as deep compaction, a deep foundation (such as piles or piers extending down around 25 feet below existing ground surface) or a heavily reinforced mat foundation designed by the structural engineer can be used to support the proposed house with a lower risk of settlement, Presented below are recommendations for shallow spread footings and slab-on-grade floor bearing on compacted structural fill. If a deep foundation or mat foundation is desired, we should be contacted to provide further design recommendations. DESIGN RECOMMNNDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, the building can be founded with spread footings bearing on compacted structural fill with a risk of settlement and possibls building distress. The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed on at least 3 feet of compacted structural fill should be desi gned fcr an allowable bearing pressure of 1,500 psf. Based on expedence, we expect initial settlement of footings designed and constructed as discussed in this section will be about I inch or less. Additional settlement on the order of 1 to 2 inches could occur if deep wetting of the subsoils were to occur. Kumar & Assocíates, lnc.Project No. 19-7.221 -4- 2)The tirntings shoukl have a minimr¡m wirJth ofl20 inc,hes ftrr contimrous walls ancl 2 feet for isolated pads. Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearirtg elevation fbr frost protection, Placement of foundations at least 36 inches below exterior grade is typically used in this area. Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 14 feet. Foundation walls asting as retaining structures should also bc designcd to rcsist a lateral earth pressure coriesponding to an equivalent fluid unit weight of at least 55 pcf. The topsoil and any loose or disturbed soils should be removed in the building area. The natural silt and clay soils in footing areas should be sub-excavated to at least 3 feet below design bearing level and to at ieast 7Yz feet beyond footing edges. The exposed soils in footing area should then be moistened and compacted. Structural fill can consist of the onsite silt and clay soils compacted to at least 98% of standard Proctor clensity at near optimum moist.ure content. A representative of the geotechnical engineer should conduct compaction testing during structural fill placement and observe all footing excavations prior to concrete placement to evaluate bearing conditions. 3) 4) FLOOR SLABS The natural on'site soils, exciusive of topsoil, can be used to support lightly loaded slab-on-grade construction with a risk of settlement similar to that for spread footings. 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 hc userl 1o reduce <ìamage cluc to shrìnkage c.racking. 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 rnad base should be placed heneath interior slahs for support. This material shoulrl consist of minus 2 inch aggregate with at least 5070 retained on the No. 4 sieve and less than 12% passing the No. 200 sieve. 5) 6) Kumar & Associates, lnc.Project No. 19.7-221 5 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 fiIl can consist of the on- site silty soils or a suitable imported granular soil devoid of vegetation, topsoil and oversized rock. 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. V/e recommend below-grade construction such as basement areas be protected from wetting and hydrostatic pressure buildup by an underdrain system. Slab-on-grade areas and crawlspaces less than 4 feet deep should not be provided with an underdrain. Where needed, 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 lo/o to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2o/o 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 1Yz feet deep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. SURFACE DRAINAGE Providing proper surface grading and drainage will be critical to keeping the bearing soils dry and limiting potential for building settlement and distress. The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation of the foundation excavations and underslab areas should be avoided during construction. Kumar & Associates, lnc.Project No. 19"7-221 -6- 2)Exterior backtill should be adjusted to near optimum moisture ancl compactecl tcr at least 95% of the maximum standard Proctor density in pavement and slab areas and to at least 90% of the maximum standard Proctor clensity in lanclscape areas. 'Ihe ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. V/e recommend a minimum slope of 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. Free-draining wall backfill (if any) should be capped with about 2 feet of the on-site soils to reduce surface water infiltration. Roof downspouts and drains should discharge well beyond the limits of all backfill. Landscaping which requires regular heavy irrigation should be located at least 10 feet from foundation walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building caused by irrigation. 3) 4) s) LIMITATIONS 'l'his study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this time. We make no warrarüy either express or implied. 'I'he conclusions anrl recommendations submitted in this report are basetl upon the data obtained from the exploratory boring drilled at the location indicated on Figure 1, 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 identified at the exploratory boring and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear to be 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 fbr 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 Kumar & Associates, lnc.Project No. 19.7-221 -7 - 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 of the recoûlmondations 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. Sincerely, Kumar & Associates, lnc. Shane J. Robat, P.E. Project Manager Reviewed by: Steven L. Pawlak, SJR/kac cc: F&M Architects (m i he(t'&ndmarç1d tects. çom ) r &fttrã Kumar & Associates, lnc.Project No. 19.7.221 Ê ì I 6¡9$LOT 66 il lr ltt'lt lr lr lr LOT 67 ì,i L i il ¡l ¡t Itl il ¡¡ 'll¡ ¡l ll ¡¡ lt Itil ¡¡ t!¡' t,Illt ¡, lt tr ll Iti I I ¡ ¡ ¡t Itll t0 10 li-t-'ti m: I r L a PI MESA RIVE APPROXIMATE SCALE-FEET 19.-7-221 Kumar & Associates LOCATION OF EXPLORATORY BORING Fig. 1 3 €{ 3 t--- L!.1t!L- I:rF-fL Ldrì FORING 1 /66 EL. 619'7' Ã 0 10 15 20 25 30 ?q 20/12 B/12 WC=95.8 DD=93.0 27 /12 WC= 1 0.2 DD=1 15 -2AA=87 I FN lffîl IÆ I0PSO|L; 0RGÂN|CS, SÁNÐY, stLT AND CLAY, F|RM, MO|ST, BROWN. cLÁY AND SILT (CL-ML); SANDY, SL|GHTLY p0ROUs, STtFf To VERY SÌIFF, SLIGHTLY MO¡ST, LIOHT BROWN. CLAY (Cl-); SANDY, SUGHTLY CALCARE0US, VERY ST|IF, SL|CHTLY M0|ST, MIXED BRoWN, LoW PL{STICITY. 9R¡YIL AND SAND (GM-SM, GC-SC); SILTY, CLAYEY, DTNST, SLIGHTLY MOIST, BROWN, SLIGHTLY CALCAREOUS, DRIVT SAMPLT, z-I].ICH I.D. CÄLITORNIA LINTR SÀMPLE. 24/12 WC=8.E 0D:1 12 DRrVt SÀMpLt, 1 318-|NCH t.D. SpLtT SPOON 5TÂN0ARD PTNTTRATION TEsT. 2¡¡17DRIYE SAMPLT BLOW COUNT. lNgtCATtS THAT 20 BL0ì¿VS 0F--I'- A 14o-POUND HAMMTR FALLING 30 INCHES WTRT RTQUIRTD TO DRIVT THE sÀMPLER 12 INCHES. NOTES THT TXPLOTÅTORY BORINC WAS DRITLTD ON APRIL 17, 2019 WITHA 4_INCH DIAMETTR CONTINUOUS FLICHT POWTR AUGER. 2. THT LOCAÌION OF THE TXPLORATORY EORING WAS MEASURTD APPROXIMATTLY BY PACING FROM FMTURTS SHOWN ON THT SITT PI-AN PROVIDÊ}. 3. THT TLEVATION OF THT TXPLORATORY BORING WÁS OBTAINTD BY INÏERPOI.ATION BTTWEEN CON]OURS ON THT SITE PLÄN PROVIDËD 4. THE TXPLORÂTORY BORING LOCATION AND ELTVATION SHOULD BT CONSIOTRTD ACCURATT ONLY TO THT DTGRET IMPTITD BY THT METHOD USTD. 5. THE LINTS BETWTEN MATERIALS SHOWN ON THT EXPLORATORY BORING LOO RTPRTSINT THÊ APPROXIMATT BOUNOARIES BTTWTEN MATERIAT TYPES AND THT TRÂNSITIONS MÀY BT GRADUAL. 6, GROUNDWATIR WÂS NOr TNCOUNTTR:O IN THT BOIING AT THT TIUT OF DRILLING. 7, IÅBORATORY TTST RTSULTS: wc = wATtR C0NTENT (%) (ÂSTM D 2216); OD : DRY DTNSITY (PCr) (ASTM D 22:6); -200 : PtRCtNIÀGt PASSTNç N0. 200 Sttvr (ASTM D r'0). 28/12 WC:6.5 DD=117 *2A0=64 56/12 7A/ 12 19-7 -221 Kumar & Associates LOG OF EXPLORATORY BORING Fig. 2 ! I SAMPLE 0F: Sondy Sllt ond Cloy FROM: Boring 1/66 @ 5' WC = 5.8 %, DD = 9J pcf br lnc.Srdl lñ .i I:,: I iiì i1 : I I :ii I Il:1rliii:,. .... . .1 NO MOVEMENT UPON WETTING,l:¡ i::,:ì à{ JJ t¡J3Ø I zo t- ô:lo UIzo C) 0 -1 *2 -3 -4 -5 -6 APPLIED - KSF t0 19-7 -221 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3 I SAMPLE OF: Sondy Ctoy FROM: Boring 1/66 q 15' WC = 8.8 %, DD = 112 pcÍ h EXPANSION UN}ÊÊ çÕNSTANT FRESSURË UPOX WTTTING JJ l¡J =tJ1 I z.o F- â Jov)z.o() 2 0 -1 -2 *3 -4 t.0 - KSF 19*7 *221 Kumar & Associates SWTLL_CONSOLIDATION TEST RISULTS Fig. 4 E I I l(+rt-tl(tm&Assclabsolnc,Geoiechnical and Materials Englneersand Environrnental kientistskumarusa.comTABLE ISUMMARY OF LABORATORY TEST RESULTSProject No. 19.7-221Lot 66SO]LTYPESandy Silt and ClaySandy ClaySandy ClayVery Sandy Clay rvithGravelU¡ICONFII{EDcoilPRESStvESTRENGTH(lsflATTERBERG LM]TSPLASTICINDEXf/o)LIQUID LIM]T(%)PERCENTPASSü'|G t¡0.200 stEvE8764GRADATIONSANDf/"1GRAI/EL(%)93NAÏURALDRYDENSITY{pcf}115112tt7I.IATURALIJ|OISTURECOlITENTPht5.87t.28.86.5SAMPLE LOCATIOIIDEPTHrfrì5101520BORIHG1/66