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Home My WebLink AboutSubsoil Study for Foundation Design 07.21.2021I (trt i;;r;ilffif,ffiniTiå *"'5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com wwrv.kumarusa.comAn Employcc Chrncd Compony Ofñce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado RECEIVED $F-F t] ? 2ü?r GARFIELD COUNTY cb r't t't u x trv DEVE LoP MENT PRELIMINARY SUBSOIL STT]DY FOR FOUNDATION DESIGN PROPOSED RESIDENCES LOTS I - A,BLOCK 1 AND LOTS I - 4, BLOCK 2 THE FAIRWAYS, BATTLEMENT MESA HOGAN CIRCLE GARFIELD COTJNTY, COLORADO PROJECT NO.2t:7-229 JULY 2I,2O2I PREPARED FOR: VINCENT TOMAST]LO c/o RUSSELL CARTWRIGHT 35IVILLOIVVTEW WAY PARACIIUTE, COLORADO 81ó35 russecart@,gmail.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION ..... SITE CONDITIONS......,... FIELD EXPLORATION SUBSURFACE CONDITIONS ...... FOUNDATION BEARING CONDITIONS ..... DESIGN RECOMMENDATIONS FOUNDATIONS. FOUNDATION AND RETAINING \MALLS FLOOR SLABS UNDERDRAIN SYSTEM SURFACE DRAINAGE... LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 . LEGEND AND NOTES FIGURE 4 through 6 - SWELL-CONSOLIDATION TEST RESULTS FIGURE 7 - GRADATION TEST RESULTS TABLE I- SIIN4MARY OF LABORATORY TEST RESULTS 1 -) - I I n -J- -6- Kumar & Associates, lnc. @ Project No. 21-7-225 PURPOSE AND SCOPE OF STUDY This report presents the results of a preliminary subsoil study for proposed residences to be located on Lots I to 4, Block 1 and Lots I to 4, Block Z,The Fairways, Battlement Mesa, Hogan Circle, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop preliminary recommendations for foundation designs. The study was conducted in accordance with our agreement for geotechnical engineering services to Russell Cartwright dated March 1,202I. A field exploration program consisting of exploratory borings was çonducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to deterrnine their classification, compressibility or swell and other engineering characteristics. The results of the field exploration and laboratory testing werc analyzed to develop recommendations 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 recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTTON The proposed residences will be one- and two- story structures with attached garages. Ground floors will be structural over crawlspace for the living areas and slab-on-grade for the garage. Grading for the structures is assumed to be relatively minor with cut depths between about 2to 5 feet, We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans change significantly from those described above, we should be notified to re-evaluate the rçcommendations contained in this report. SITE CONDITIONS The subject site was vacant at the time of our field exploration. The ground surface is sloping down to the east at an estimated grade of about 10 percent. Vegetation consists of grass and sparse weeds. Kumar & Associates, Inc. o Project No.2l-7-229 -2- FIELD EXPLORATION The field exploration for the project was conducted on March 26,2021. Four exploratory borings were drilled at the locations shown on Figure I to evaluate the subsurface conditions. The borings were advanced with 4-inch diameter continuous flight augers powered by a truck- mounted CME-458 drill rig. The borings were logged by a representative of Kumar & Associates, Inc. Samples of the subsoils were taken with l%-inch and 2-inch I.D. spoon samplers. 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-l586. 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 Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about 1 foot of topsoil overlying mainly sandy silt soils to depths between 12 and 20 feet where dense, siþ clayey sand and gravel with cobbles was encountered to the maximum explored depth of 24 feet deep. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and possible boulders and drilling reftrsal was encountered in the deposit at Borings I and4. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed drive samples of the silt soils, presented on Figures 4 through 6, indicate low compressibility under existing low moisture conditions and light loading and varied low collapse to low swell potential when wetted under constant light surcharge. Results of gradation analyses performed on small diameter drive samples (minus l%-inch fraction) of the coarse granular subsoils are shown on Figure 7. The laboratory testing is summarizedinTable 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist. Kumar & Associates, lnc, o Project No.21-7-229 -J- FOUNDATION BEARING CONDITIONS The upper silt soils encountered in the borings possess low bearing capacity and varied compression/expansion potential when wetted. Our experience indicated the upper fine-grained soils are mainly compressible when wetted under loading. The underlying gravel soils possess moderate bearing capacity and typically low settlement potential. Spread footings placed on the upper fïne-grained soils can be used for support of the proposed residences with a risk of foundation movement. A lower risk option would be to extend the bearing level down to the underlying gravel soils with a deep foundation system such as drilled piers or micro-piles. Provided below are recommendations for a spread footing foundation system. If recommendations for a deep foundation system are desired, we should be contacted to provide them. DESIGN RECOMMENDATIONS FOTINDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the building be founded with spread footings bearing on the natural fine-grained soils. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural fine-grained soils should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about I inch or less. Additional post-construction differential foundation movement could occur if the bearing soils become wetted. The magnitude of additional movement would depend on the depth and extent of wetting but could be on the order of about I to l% inches. 2) The footings should have a minimum width of 18 inches for continuous walls and 2 feet for isolated pads. 3) Exterior footings and footings beneath unheated areas should be provided with adequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this aÍea. 4) 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. Kumar & Associates, Inc. o Project No.21-7-225 -4- Foundation walls acting as retaining structures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. Topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the firm natural fine-grained soils. The exposed soils in footing area should then be moistened and compacted. A represent¿tive of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION AND RETAINING \MAILS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting of the on-site fine-grained soils. Cantilevered retaining structures which are separate frorn the residences and can be expected to deflect sufficiently to mobilize the full active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 45 pcf for backfrll consisting of the on-site fine-grained soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffïc, construction materials and equipment. The pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90o/o of the maximum standard Proctor density at a moisture content near optimum. Backfill placed in pavement and walkway areas should be compacted to at least 95o/o of the maximum standard Proctor density. Care should be taken not to overcompact the backflrll or use large equipment near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms ofthe footings can be calculated based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the 5) 6) Kumar & Associates, Inc, @ Project No. 21-7-229 5 sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The coeffïcient of friction and passive pressure values recommended above assume ultimate soil strength. Suiøble factors of safety should be included in the design to limit the strain which will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soilso exclusive of topsoil, are suitable to support lightty loaded slab-on-grade construction with a risk of movernent similar to that described above for 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 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 free-draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than 2olo passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% of maximum standard Proctor density at a moisture content near optimum. Required frll can consist of the on-site soils 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 runoffcan create a perched condition. We recommend below-grade construction, such as retaining walls, crawlspace (greater than 4 feet deep) and basement areas (if any), 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 lo/o to 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 Kumar & Associates, lnc. o Project No,2l-7-229 -6- the No. 4 sieve and have a maximum size of 2 inches- The drain gravel backfïll should be at Ieast lYz 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 limiting subsurface wetting and potential building movement. The following drainage precautions shouldbe observed during construction and maintained at all times after the residences havç been completed: 1) Inundation ofthe foundation excavations andunderslab areas shouldbe avoided during construction. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95a/o of the maximum standard Proctor density in pavement and slab areas and to at lçast 90% of the maximum standard Proctor density in landscape areas. 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 paved areas. Free-draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site soils to reduce surface water infiltration. 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 l0 feet from foundation walls. 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 warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory borings drilled at the locations 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 Kumar & Associates, Inc, @ Project No.21:l-229 -7 - subsurface conditions identified at the exploratory borings 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 so that re-evaluation of the recommendations may be made. This report has been prepared for the exclusive use by our client for planning and preliminary 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 monitor the implementation of our recommendations, and to veriff 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. Respectfully Submitted, Kumar & Associates, Inc. James H. Parsons, P.E. Reviewed by: Steven L. Pawlak, P.E JHP/kac ll. W 5866t Kumar & Associates, lnc. Ô Project No. 21"7.229 ( $+ ts69't6'¿I't ú a¿l{l¡vt lþ4.lqtol ônt ^þtc{ toultl.l AqÍa ,ñ$f cff{H Sté'lili íttl'+lllûtÃ\t unlù asÍwr t i¡€<d|., laâ¿ ãnffial rr t.Étrd.ô h{æl.t t.l tdmwı|. IS ßfu ød ll&r fr¡abCq Or\:I l5 l!71ftA'tln|t aâ ¿!r.t ^7 taul^ Íı. Òl .últ.l ¡t4>øþ æørô,c, t|'.4 ^îEq øln| o la/l.l ol lt at'J:'21' lf, o APPROXIMATE SCALE_FEET 21-7-229 Kumar & Associates LOCAT]ON OF IXPLORATORY BORINGS 1Fig. I I ñ à BOR]NG I BORING 2 BORING 3 BORING 4 0 2s/12 WC=4.8 DD=98 -2OO=92 o 4s/12 45/12 WC=5.7 DD= 1 07 ss/12 5 22/12 WC=5.8 DD= 1 01 28/12 WC=3.8 DD= 1 04 18/12 WC=4.0 DD= 1 03 5 24/12 26/12 23/12 23/12 24/12 10 25/12 WC=4.8 DD= 1 09 t024/t2 22/12 WC=4.5 DD=99 24/12 WC=6.4 DD=99 f-bJ tJJ LL I-F.fL l¡Jo 15 s2/12 25/6, 50/5 WC=4.6 +4=26 -2OO=43 t5 l-t¡J l¡J lJ- I-F-fLf¡lô 31/12 WC=5.5 DD=1 1 5 -2OO=94 40/12 20 20 43/12 50/1 50/2 25 25 30 50 Fig. 2LOGS OF EXPLORATORY BORINGS21 -7 -229 Kumar & Associates I I LEGEND N m W ! i TOPSOIL: SILT, SANDY, ORGANICS, FIRM, SLIGHTLY MOIST, BROWN SILT (ML): SLIGHTLY SANDY TO SANDY, SANDIER WITH DEPTI{, SLIGHTLY CLAYEY, SLIGI{TLY CALCAREOUS, VERY STIFF TO HARD, SLIGHTLY MOIST, TAN. GRAVEL (cC-cM): SANDY, SILTY, CLAYEY, COBBLES, POSSIBLE BOULDERS, DENSE, SLIGHÏLY MOIST, GREY BROWN. DRIVE SAMPLE, z-INCH I.D. CALIFORNIA LINER SAMPLE. DRTVE SAMPLE, 1 3/9-INCH l.D. SPLIT SPOON STANDARD PENETRATION TEST ,^I.^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 49 BLOWS OF A 140-POUND HAMMER+r/ tz FALLTNG Jo rNcHEs WERE REQU|RED To DRIVE THE SAMPLER 12 lNcHES. I enacrrcAL AUcER REFUsAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 26, 2021 WITH A 4_INCH DIAMETER CONTINUOUS_FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS ARE PLOTTED TO DEPÏH. 4. TIIE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT ÏHE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (pct) (¡Sru D2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (NSTU OOSIS); -200= PERCENTAGE PASSING NO. 2oO SIEVE (ASTM 01140). 21 -7 -229 Kumar & Associates LEGEND AND NOTES Fig. 3 I E ¡ ñ ò:q JJ UJ =În I z.ot- ô =o anz.o() 1 i I I I I SAMPLE OF: Sondy Sill FROM;Boringl@4' WC = 3.8 %, ùD = 101 pcf NO MOVEMENT UPON WETTING 0 -1 -2 -3 f.0 àq JJl¡l =an I zo t- f¡ Jo anz.o C) 2 1 o -t -2 .0 - KSF t0 SAMPLE OF: Silt ond Cloy FROM:Boringl@15' WC = 5.5 76, DD = 115 pcf l¡ d od I I I I EXPANSION UNDER CONSTANT PRESSURE UPON WETTING l -i I I I .l l I l l I l I l i.. .." I i 21 -7 -229 Kumar & Associates SWELL-CONSOLIDATION TEST RTSULTS Fig. 4 r I 1 0 JJl¡l =an -l I zo F ô =ot _<zo() -4 -5 x 1 JJ l¡Jão I zo t- o =ou1 -cz.o(J -3 às 1,0 PRESSURE . KSF t0 SAMPLE OF: Sondy Silt FROM:Borln12e^2.5' WC = 5.7 %' DD = 'l 07 pcf I ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING \ \ \ I I l I SAMPLE OF: Sondy Silt FR0M:Boring2@10' WC = 4,J Y", DD = 99 pcf n@ ld @nr opot oñy þ üoffiÞh3 dd. tu Hhg EFt dÈll not ba Eprodr¡sd. q6pt h Ml, rïthout ü. ìfrm oppml d Xuñd orú Aþolol* |rc. stllll Con-lttot¡ú l-thg Ëfoø.d ¡oñdo€ rlh As'll¡ D-,15/t!. I I L l -1 l I .1. EXPANSION UNDER CONSTANT PRESSURE UPON WETTING I i I I l I i i l I r00 SWELL-CONSOLIDATION TEST RESULTS Fig. 521 -7 -229 Kumar & Associates I ri SAMPLE OF: Sondy Silt FROM:BoringS@4' WC = 3.8 "/a, DD = 104 pcf t-_ EXPANSION UNDER CONSTANT PRESSURE UPON WETTING ì ) JJl¡l =U' I zotr ô Jo anz.o(J N JJ l¡J =v, I z,otr ô =o anzoo 1 0 -1 -2 1 0 -1 -2 t00 SAMPLE OF: Sondy Sìlt FROM:Borlng4@10' WC = 4.8 %, DD = 'l 09 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING I I l I l -l-f'i I I I lrb ilþr¡l oflhc I i t i' I I I Ì I i I i i Ì f.0 00 Fig. 6SWELL-CONSOLIDATION TEST RESULTS21 -7 -229 Kumar & Associates E I z ¡: HYDROMETËR ANALYSIS SIEVE ANALYSIS ÎITIE ÊEADIiGS 2¿ BnS 7 HnSur! murN roú|tr tutN at rtô ¡t U.S. SINDAno SERIES CLEAR SOUARE OPÊ{IÑOs I I I I I i I I ! i I I I i I i I I I I ì t ¡ I I I I I I I SAND GRAVEL I I FINE MEDIUM FINE COARSE c6 U E roo 90 ao 70 ûo 50 ,40 30 20 to o lo 20 30 40 30 30 70 80 90 t00 I 0 ,o05 .300 r .aæ .125 PARTICLES INOF CLAY TO SILT COBBLES GRAVEL 26 % SAND 31 LIQUID LIMIT SAMPLE OF: Silty Cloycy Sond ond Grovel ,a PLASTICITY INDEX SILT AND CLAY 1ı % FROM: Borlng ,l O l¡l' lho!6 læl rolull! opply only lo tho bsllng rcport sholl not b! rproducld, rxccÞl ln tull, vlthout lhq wtltton oppfovql ol Kumqr & Agtoclolqt, lnc. shv. onoly!|3 ltlling ¡s Þrrfomld in occordonce rlth ASTM D6913, ASTM D7928, ASTU C156 qnd,/or AsfU Dll¿o. 21-7-229 Kumar & Associates GRADATION TEST RESULTS Flg. 7 l(+rliiffififfifffi,Hi;'.-TABLE 1SUMMARY OF LABORATORYTEST RESULTSSOIL TYPESandy SiltSilt and ClaySandy SiltSandy SiltSlightly Sandy SiltSandy SiltSandy SiltSandy SiltSandy SiltSiþ Clayey Sand andGravel(psf)UÌ'ICONFNÊDCOMPRESSIVESTRENGTHP^lPLASTCINDEXATTERBERG UMITS{%lTIQUID LIMTÍ9243PERCENTPASSING NO.200 stEvE941J{%)sAt¡D26GRAOATION{%}GRAIÆL99103109focflNAIURALDRYDENSITY101115t079998t045.55.74.34.83.86.44.04.84.6{%lNÂTURALMOISTURECONTEI{T3.85I2V201I41051014rfrtDEPTH4J4SAIi|PLE LOCATIONBORING12No.21-7-2ß