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HomeMy WebLinkAboutSubsoils Report for Foundation DesignI(rlt Im&lcc¡siaüû"m"* Geo&cüniiuall andi M&dalb Fn$ineem anrdr tsrüi¡rcr,rfi €ÍTtøll Scier¡däg An ffi.çoOmucf Conpcnry 5{fø0Cbmú[yRoûd l-ç[ Glenmomd $pning$, Ct 8[60]lt uüolml (97@) 945-Z$8S ft<:(g/0)%tr4i54 email: k*gjþnrr¡r,oo@)klümørs6e€otnt www,kumarusa.com Olffi¡clloaadrsrûr;: Ihrvto:(TltQ)lFanltar;CidlmadoSþä.rgr"FrorfCrolüliøs,GllqrwoodSprings,ardl$¡nr¡a¡ft(}*nn$fCiolbtrådo¡ SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDE¡{CE 3554 COUNTY ROAD 2I4 SILT. COLORADO PROJECT NO.22-7-406 JULY 7,2022 PREPARED FOR: DAYBREAK CONSTRUCTION ATTN: DANA YERIAN P.O. BOX 587 GLEÀIWOOD SPRINGS, COLORADO 81602 davbreakconst@hotmail.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY. PROPOSED CONSTRUCTION ........ SITE CONDITIONS... FIELD EXPLORATION ..... SUBSURFACE CONDITIONS FOT}NDATION BEARTNG CONDTTIONS DESIGN RECOMMENDATIONS ............... FOUNDATIONS FOUNDATION AND RETAINING WALLS FLOOR SLABS UNDERDRAIN SYSTEM ..... SURFACE DRAINAGE........, LIMITATIONS FIGURE, I - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGIJRE,3 - LEGEND AND NOTES FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS TABLE I- SUMMARY OF LABORATORY TEST RESULTS ......- 1 - 1 1 1 -2- 1 -J- -3- -3- 4- -5- -5- -6- lûmn&*¡rccåh+lhno P[ìoiG€t¡{oì"ZÈã-400 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at 3554 County Road 214, Silt, Coloraclo. The project site is sholi'n on Figure l. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to Daybreak Construction dated ïu:ne 1,2022. A field extrrloration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Sarnples of the subsoils obtained during the field exploration rvere testecl in the laboratory to determine their classifìcation, compressibility or swell and other engineering characteristics. The results of the 1ìelcl exploration and laboratory testing were analyzed to develop recornmendations for foundation types, depths and allowable pressures for the proposed building fcrundation. This report summarizes the data obtairred during tliis study and presents oul conclusions, design recomrnendations and other geotechnical engineering consiclerations based on the proposed constmction and the subsurface conclitions encountered. PROPOSED CONSTRUCTION The proposecl residence will be a one-story wood-frame structure over a partial basement with attached garage. Ground floors will be a combination of slab-on-grade and strucfural over crawlspace. Grading for the structure is assumed to be relatively miuor with cut depths between about 3 to l0 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. tf building loadings, location or grading plans change significantly from those described above, we shoulil be notified to re-evaluate the recommendations contained in this report. SITE CONDITIONS The subject site was developed with a single-story residence over a lower basement level (which will be rernoved). The grourd surfäce is relatively flat with a gentle slope down to the south. An inigation ditch was tlowing along the west property line. Vegetation consists of landscaped lawn. bushes and deciduous trees. FIELD EXPLORATION The field exploration for the project was conducted on June 13, 2A22. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The lffmnr$AseæhËeqlkc;@ Projcctfio-2ããlffi a borings lvere 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 Kunar & Associates, Inc. Samples of the subsoils were taken rvith a 2-inch I.D. spoon sampler. The sarnpler was cldven into the subsoils at rrarious depths with blows from a 140-pound harntner falling 30 inches. This test is similar to the standard penettation 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 slrown on the Logs of Exploratory Borings, Figure 2. The sarnples 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 encountereci below about %lootof topsoil consist of loose to vety loose, clayey to very clayey sand down to the maxirnum explored clepth of 40 feet. A layer of medium stiff, sancly clay was encountered in Boring I below the topsoil fromYz to 4 feet deep. Laboratory testing perftrrmecl on samples obtained fiom the borings inoluded natural moisture content and density and finer than sand grain gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed drive samples of the very clayey sand, presented on Figure 4. indicate low to moderate compressibility under conditions of loacling and wetting. The laboratory testing is summarized in Table 1. No fì'ee lvater was encountered in the borings at the time of drilling and the subsoils were moist to very moist. FOUNDATION BEARING COI\DITTONS The clayey sand soils encountered in the borings possess low bearing capacity and low to moderate settlement potential. Boring I was drilled to a maximum depth of 40 feet and no dense granular soils or hard bedroc,k rnaterial was encountered. Lightly loaded spread t-ootings plaoed on the clayey sand can be used for support of the proposed residence with a risk of settlement. Provicling a clepfh of sfnrcfilral fi11, lypically 3 feet, helow the spread fbotings can reduce the risk of settleruent. Provided belorv are recomlnendations for a spread footing foundation system bearing on the natural soils. If recommendations for strucfi.ral fill are desired, we should be contacted to provide thern. l{rntrr & ArcotfrrÉer¡o llrr- @ ftsieatlûo.!ãl.|00 -3- DESIGN RECOMMENDATIONS FOLINDATIONS Considerìng the subsurface conditions encountered in the exploratory borings and the nature of the llroposed construction, we recommend the building be founded with spread footings bearing on the natural soils. The design and constnrction criteria presented below should be observed tbr a spread footing foundation systern. 1) Footings placecl on the undisturbed natural soils shoulct be clesigned for an allowable bearing pressure of 1,500 psf. Based on experience, we expect seftlernent of footings designed and constructed as discussed in this section will be about lY" inch or less. 2) The footìrrgs should have a minimum width of 20 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 al¡ove their bearing elevation for û'ost pt'otection. Placement of foundations at least 36 inches below exterior grade is typically used in this area. 4) Continuous foundation wal1s should be heavily reinforced top and bottotn to span local anomalies and better r¡'ithstand differential movement such as by assurning an uûsupported length of at least l4 feet. Formdatiou rvalls 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. 5) All existing fill, topsoil and any loose disturbed soils should be rentoved and the footing bearing level extended down to the relatively firm natural soils, The exposecl soils in footing areas should then be moistened and compacted. If water seepage is encountered, the footing areas should be dewatered lrefore concrete placement. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOUNDATION AND RETAINiNG WALLS Foundation r.valls ancl retaining stmctures which are laterally supported and can be expected to undergo only a slight arnount 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 soils. Cantilevered retaining süructures which are separate frorn the residence ancl can be expectecl to cleflect sufficiently to ruobilize the full active ea$h pressure condition should t{smn&*ssæhh*rl}E*@ F[oþatlllio"&Þ741F -4- be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 45 pcf for backfill consisting of the on-site soils. All f'ounclation arrd retaining structures should be designed for appropriate hyclrostatic artd surclrarge pressures such as adjacent footings, traffic, construction materials and equipment. The pressures recommended above assune drained conditions behind the walls and a horizontal backfill surface. The builclrrp of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining stntcture. An underdrain should be prorìded 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. Backfìll placed in pavement attd walkway areas should be compacted to at least 95o/o of the maximum standard Proctor density. Care should be taken not to overcornpact the backfill or use large equipment near the wall, since this could calrse excessive lateral pressure on the wall, Some settlement of deep foundation wall backfill should be expected, even if the traterial is placecl correctly, and could result in clistress to t'acilities constructed on the backfitl. The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on tlie foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the boltoms of the footings can be calculatecl based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluici unit weight of 375 pcf. The coefflcient of friction and passive pressure values reconrmended above asswï.e ultimate soil strength. Suitable factors of safety should be included in the design to limit the strain which will occur at the ultinate strenglh, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads shoulci be cotnpacted to at least 95% of the maxirnum standard Prcctor density at a moistwe content near optirnurn. FLOOR SLABS The natrral on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-gratle construction. To reduce the effects of some differential movement, floo¡ slabs should be separated from all bearirg walls and colurnns with expansion joints which allow unrestrained veftical rnovement. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirenents for joint spacing and slab reinforcement should be established by the ciesigner based on experience and the intended slab use. A minimmn 4-inch layer of relatively well graded sancl and gravel should be placed beneath basement level slabs ttrr support. This material should consist of minus 2-inch aggregate r.vith at least 50% retained on the No. 4 sieve and less thatl2o/o passing the No.200 sieve. l{m¡n & å,saûchüE$} lh& @ Ptoi¡eøt;t{o;2È?-406 -5- All fill materials for support of f'loor slabs should be compacted to at least95Yo of maximunr standard Proctor clensity at a moisture content near optimum. Required fill can consist of the on-site granular soils devoid of vegetation, topsoil and oversized rock^ UNDERDRAIN SYSTEM Although fì'ee water was not encountered during our exploration, it has been our experience in the area that local perched groundrvater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. 'We recomrnend 6.1eq,-grade construction, such as retaining walls, crawlspace and basement ateas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. The drains should consist of clrainpipe placed in the bottom of the wall backfill surrourded above the invert level vi'ith free-draining granular material. The drain should be placed at each level of excavation and at least 1 foot below lowest adjacent tìnish gracle and sloped at a minimum lYo to a suitable gravity outlet or sump and purnp. Free-draining granular material usecl in the underdrain system should contain less than 2o/opassing the Nr¡. 200 sieve, less than 50% passing tlre No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least I Yzfeet deep arrd covered with filter fabric such as Mirafi 140N or 160N. SURFACE DRAINAGE The follor.ving drainage precautions should be observed cluring construction ancl maintained at all times after the residence has been completed: 1) Inrndation of the founclation excavations and underslab areas should be avoided during constnrction. 2) Exterior backfill should be adjustecl to near optimum moisture and compacted to at least 95Yo of the maxirnun standard Proctor density in pavement and slab areas and to at least 90o/o o{ the rnaximum standard Proctor density irr larrdscape areas. 3) The ground surface surrounding the exferior of tire building should be sloped to clrairr away from the foundation in all directions. We recommend a minimum slope of 6 inches in tlre first 10 fbet ìn unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. Free-chaining rvall backfill should be covered with filter fabric and capped with about 2 feet of the on-site finer-graded soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of ail backfill. 5) Landscaping which requires regular hear.y irrigation shoulcl be located at least 5 feef from foundation walls. K¡mr & *sosciates, lnc. o Froj'cnt lt{e., Ær-,T406 -6- LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this areaatthis 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 subsurface conditions idèntified at the exploratory borings and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during conskuction 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 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 veri$ 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, Ku¡nar & Associ:rte;, lnt James H. Parsons, P Reviewed by: Daniel E. Hardin, P.E. JHP/kac TL )4 /z 7. 5866t Kumar & Associates, lnc. n'Project No. 22-7-406 I Pumphouse + Lri fr Sgg030'26,,8 I pol I I þ.1' I I I â cû (o il 2gg.g7l .8OR¡NG I 3n.Single fo'nily residence Wood frcme construction 1554 Co. Rd. No. 2'14 K¡RING 2 IRRrcANON DITCH j .l X X X F.r l+v x+x'+x Glsvel drivewn 1 APPROXIMATE SCALE-FEET + c! C\l 17'00 t/ - )I 22-7 -446 Kumar & Associates LOCATION OF TXPLORATORY BORINGS Fig. 1 = BORING 1 EL. 100.5' BORING 2 EL. 1 00' 0 0 6/ 12 e/ 12 5 5/12 54/ 12 WC=20.6 DD= 1 O2 10 5/12 DD=1 1 1 3/12 WC=16.0 DD=1 10 10 15 153/ 12 s/ 12 WC=17.8 DD= I 08 -20Q=43 t- L¡lIJL I-FfLl¡lÊ 20 7 /12 WC=19.2 DD= 1 06 20 f-t¡l ùl t! tTt-o- t¡JÊ 25 25 50 50 35 55 4t4A Fig. 222-7 -406 Kumar & Associates LOGS OF TXPLORATORY BORINGS I ç N,6 e 4 LEGEND TOPSOIL. CLAY, SANDY, ORGANIC, FIRM, MOISÏ, DARK BROWN. CLAY (CL); SÀNDY, MEDIUM STIFF, MOIST, BROWN. SAND (SC); CLAYEY IO VERY CLAYEY, SILTY, LOOSE TO VERY LOOSE, VERY MOIST, BROWN. DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE. ezr,¡ DRTVE SAMPLE BLOW COUNT. IND|CATES THAT 6 BLOWS OF A 14o-POUND HAMMER"/ . . FELLING 50 INCHES WERE REQUIRED TO DRIVE THE SAMPLER .I2 INCHES. .-> BEPTH AT WHICH BORING CAVED. NOTES 1 THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 13, 2422 WITH A 4-INCH_D¡AMETER CONTINUOUS-FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE S E PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXFLORATORY BORINGS WERE MEASURED BY HAND LEVEL AND REFER TO THE EXISTING FINISHED FLOOR EL. 1OO" ASSUMED. 4. TIIE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE MEÏHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENÏ THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AÏ THE TIME OF DRILLING 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D2?16); DD = DRY DENSIIY (pcf) (ASTM D2216); -ZQO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1140). Fig. 3LEGEND AND NOTES22-7 -406 Kumar & Associates 3 T SAMPLE OF: Cloyey Sond FROM:Boringl@5' WC = 20.6 %, Ðù = 142 pcl I I j :i il i ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I ': 1 i-:i-l¡ iii ''!r D-{46. 1 )q JJ LtJ Ø I z,otr â =o anz.(f, (.) o -1 -2 -3 4 -6 PRISSURE . KSF IO 100 22-7-446 Kumar & Associates SWELL_CONSOLIDATION TTST RESULT Fis. 4 9 = : i SAMPLE OF: Cloyey Sond FROM: Boring 1 @ 10' DD = 111 pcf ÁÐDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING tôgìad. ftô ¡n D-45t6. ,1 ¡q JJ L¡l =(n I zo =o JoØzo 0 -1 -2 -3 -4 _q -6 1 t.0 APPLIED PRESSURE - KSF 10 SWTLL_CONSOLIDATION TIST RTSULT Fig. 522-7 -406 Kumar & Associates l(t t*ffii[ffiffi'$Ë;å*'* TABLE 1 SUMMARY OF LABORATORY TEST RESULTS No. 22-7-406 Clayey Sand Clayey Sand Clayey Sand Clayey Sand Clayey Sand 43 102 111 il0 108 106 20.6 16.0 t7.8 19.2 5 10 0I 15 20 2 1 SOIL TYPEUQUID LIMITDEPÏHBORING GRADATION UNCONFINED COMPRESSIVE STRENGTH PLASTIC INDEX PERCENT PASSING NO. 200 stEVE NATURAL DRY DENSITY NAÏURAL MOISTURE CONTENT SAND %t GRAVET (%)