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HomeMy WebLinkAboutSubsoil Studyl(+rlffiiilffiffiixü-- An Emdoycc Owncd ComPonY 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945'7988 fax (970) 945-84s4 email: kaglenwood@kumarusa.com www.kumarusa.corn Ofiìce Localiors: Denver (HQ), Par*er- Cotorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED KLASE RESIDENCE LOT 12, BLOCK 4, BATTLEMENT CREEK VILLAGE I2I BOULDER RIDGE GARFIELD COUNTY, COLORADO PROJECT NO.2l-7-121 FEBRUARY 12,2021 PREPARED FOR: RUSSELL CARTWRIGHT 35 WILLO1VVIEW \ryAY PARACUTE, COLORADO 81635 russecart(Osmail.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION ......... SITE CONDITIONS... FIELD EXPLORATION SUBSURFACE CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS .......... FOUNDATION AND RETAINING WALLS FLOOR SLABS UNDERDRAIN SYSTEM .,.... SURFACE DRAINAGE LIMITATIONS .......... FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2. LOG OF EXPLORATORY BORING FIGURE 3 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1. SUMMARY OF LABORATORY TEST RESULTS ...- I - ..........- 1 - .......- I - -t - 1 ,.....- 3 - ......- 3 - ......- 4 - ......- 5 - ......- 5 - ......- 6 - ..-6- Kumar &Assoclates, lnc. o Project No. 214-121 PT}RPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for the proposed Klase residence to be located on Lot 12, Block 4, Battlement Creek Village, 121 Boulder Ridge, Garfreld County, Colorado. The project site is shown 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 Russell Carh,vright dated January 12,2021. An exploratory boring was drilled to obtain information onthe subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classifrcation, compressibility or swell and other engineering characteristics. The results of the fiçld exploration and laboratory testing were 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 conçlusions, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The residence will be a single-story wood frame structure over a walkout basement level with attached garageat the main level. Ground floors will be slab-on-grade. Grading for the structure is assumed to be relatively minor with cut depths between about 2 to 8 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 recommerdations contained in this report. SITE CONDITIONS The lot was vacant and the ground surface appeared mostly natural at the time of our field exploration. The terrain is strongly sloping down to the south. Vegetation consisted of grass, weeds and sagebrush. The Colorado River is approximately Ya mile north of the site and considerably lower in elevation. Kumar & Aseociales, lnc. o Prqú.Nø.21-7-121 -2- FIELD EXPLORATION The field exploration for the project was conducted on January 14,2021. One exploratory boring wæ drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring was advanced with 4 inch diameter continuous flight augers 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 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-l58ó. 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 retumed 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 of about I foot of topsoil overlying very stifl sandy clayey silt to 12 feet depth where underlain by relatively dense, silty clayey sandy gravel and cobbles with boulders down to the drilled depth of l8 feet. Laboratory testing perfbrmed on samples obtained from the boring included natural moisture content and density, and f,ner than sand grain size gradation analyses. Results of swell- consolidation testing performed on a relatively undisturbed drive sample of the clayey silt, presented on Figure 4, indicate low to moderate compressibility under existing moisture conditions and light loading, with a low expansion potential when wett€d under çonstant light surcharge. The laboratory testing is summarized in Table l' No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist. Kumar &Associates, lnc. o Project tlo.2l-7-l2l -3- DESIGN RECOMMENDATIONS FOTJNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, we believe the building can be founded with spread footings bearing on the natural soils with some risk of movement. The risk of movement is primarily if the bearing soils were to become wetted and precautions should be taken to prevent wetting. Based on our experience in the area, the clayey silt soils are not expansive. The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed onthe undisturbed natural soils should be designed for an allowablebearingpressure.P.Basedonexperience'weexpect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. Some additional settlement could occur if the bearing soils become wetted. The magnitude of the additional settlement would depend on the depth and extent of the wetting but may b e on the order of táto I inch. Z\ 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 foundationr u*191:6 i*hæ-below exterior grade is typically used in this area. 4) Continuous foundation walls should be well reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 14 feet. Foundation walls acting as retaining structures should also be designed to resist laterat earth pressures as discussed in the "Foundation and Retaining Walls" section of this rePort- 5) All existing frll, topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the firm natural soils. The exposed soils in footing area should then be moistened and compacted. 6) A reprosentative oftho geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. Kumar & Associatæ, lnc. o ProiæINo.21-7.121 -4 FOUNDATION AND RETAINING WALLS 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 50 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are separate from the residence and can be expected to deflect sufficiently to mobilíze 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 40 pcf for backfill consisting of the on-site soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, 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 90% of the maxrmum standard proctor density at a moisture content near optimum. Backfill 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 backfill 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 tho foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coeffrcient of friction of 0.35. Passive pressure of compacted backfrll against the sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The coefficient of friction and passive pressure values recommended above assums ultimate soil strength. Suitable 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 agâinst Kumar & Associatee , lnc. o Project llo. 21-7-121 -5- 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 soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction. The clayey silt soils are typically compressible when wetted and precautions should be taken to prevent wetting of the subgrade soils. Designing the slab for expansive çonditions is not needed based on our experience in the area' 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 2% passing the No. 200 sieve. Alt 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 fill can consist of the on* site soils devoid of vegetation, topsoil and oversized rocks' UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our experience ln the area that local perched groundwater can develop during times of heavy precipitation or seasonal runoff, Frozen ground during spring runoffcan also create a perched condition. We recommend below-grade construction, such as retaining walls, crawlspace and basement areas, 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 l% to Kumar & Associates, lnc. o Project No.21-7-121 -6- a suitable gravrty outlet. Free-draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, Iess than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least l% feet deep. SURFACE DRAINAGE Positive surface drainage is a very important aspect of the project to prevent wetting of the bearing soils. 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. Z) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95%o of the mæ<imum standard Proctor density in pavement and slab areas and to at least 90% ofthe maximum standard Proctor density in landscape areas. 3) The ground surface surrounding the exterior of the building should be sloped to drain away ûom 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 l0 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, such as sod, and lawn sprinkler heads should be located at least 10 feet from foundation walls. LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engíneering principles and practices in this area at this time. We make no waranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory boring drilled at the location indicated on Figure l, 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 Kumar & Associates, lnc. o Project l{o.21-7-121 -7 - 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 extrapolation of the subsurface conditions identified at the exploratory boring and variations in the subsurface conditions mây not become evident until excavation is performed. If conditions encountered during consfruction 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 pmject 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, trnc. James H. Parsons, E.I. Reviewed by: David A. Young, JFIPlkac cc: AlldraftDesign ) I Kumar & Associates, lnc. ú Project No.21"7.121 FJ 6$U nI t:"] 't]l'\'t'ul Ë 1,28?'661 .e449 I At ¿ r ssss 1 n $r R\DGÉ d.sþ 3 {¡6 \i \)'Ê [" .t. 30 6 { 13 1s$1Û $ r ,i o'*' 121 BOULDER RIDGE t LOT t2 o BORING f g,\)\d 1T lsÛu ? $ F' APPROXIMÀTE SCALE.FEET Fig. 1LOCATION OF EXPLORATORY BORING21 -7 -121 Kumar & Associates BORING 1 LEGEND 0 TOPS0IL; SANDY CLAYEY SlLi WITH ORGANICS, FIRM, MO|ST, BROWN. 35/12 SILT (ML); CLÂYTY, SANDY, VERY STIFF TO STIFF, SLIGHTLY MOIST, TÀN. 5 zaln WC=3.8 0D=89 -200=84 ffi F I GRAVEL (GC-GM); WITH BASALT ROCKS TO COBBIT AND BOUTDER SIZE, SANDY, CLÀYff, SILTY, DENSE, SLIGHTLY MOIST, UGHT BROWN. 21/12 WC=4.7 DD=l 03 le/12 WC=3.8 DD=99 -200=86 DRIVE SAMPIT, z-INCH I.D. CAUFORI.IIA UNER SAMPI.E. t-- L¡J ¡¿lL I :E!-fL¡¡lo 10 DRtVt SAMPLE, r 3/8-INCH l,Ð. SPUT SP00N STANDAR0 PENETRATION TEST. 15 ,"r.^DRIVE SAMPLE BL0w COUNT. INDICATES THAT 55 BLOWS 0F14 tL ^ 140-pouND HAMMER FALLING J0 tNcHEs WERE REoUIRED TO DRIVE THE SAMPTER 12 INCHES. I pRlcncr AUGER REFUsÀ1. I 50/t.s 50/.25 NOTES I. THT EXPLORATORY BORING IVAS DRILLED ON JANUARY 14,2O2I WTH A 4-INCH DIAMETER CONTINUOUS FTIGHT POWER AUGER. 20 2. THT LOCATION OF THE EXPLORATORY BORING WAS MEASURED APPROXIMATILY BY PACING TROM FEAIURES SHOWN ON THE SIÍE PI.ÀN PROVIDED, 3. THE ELEVATION OF THE EXPLORATORY BORING WÀS NOT MËASURED AND THT LOG OF THE EXPLORATORY BORING IS PLOTTED ÏO DEPTH. 1. THE EXPLORATORY BORING LOCATION SHOULD BE CONSIDEREO ACCURATT ONLY TO THE OEGREE IMPLIED BY THE METHOD USTD. 5. THE LINTS BET'IIETN MATERIALS SHOWN ON THE TXPLORATORY BORING LOG REPRESENT THE APPROXIMATE BOUNDÀRIES BETWEEN MATERIÀL TYPES AND THE TRANSITIONS MAY BI GRADUAL. 6. GROUNDWATER WÂS NOT TNCOUNTERED IN THE BORING ÀT ÏHg TIME OF DRILUNG. 7. LÁBORATORY TESÏ RESULÏS: WC = IYATER CONTENT (16) (ASTM D 2216); DD = DRY DENSIw (pcf) (ASTM D 2216); -200 = PERCENTÀGE PASSING N0. 200 SIEVE (ÀsTM Ð 1t40). Fig. 2LOG OF EXPLORATORY BORINGKumar & Associates?1 -7 -121 ! € o SAMPLE OF: Sondy Cloyey Sill FROM:Boringl@.7' WC = 4.7 %, ùD = 103 pcf 1 o j-1 l¿l =vlt-z zotr $-sotnzo<)-4 t.o 21-7-121 Kumar & Associates SWELL-CONSOLIDATION TEST RESULT Fig. 3 lcrt t ftnlar &lsgot}¡b, h.c Geotectr¡ical and Mat€dals Êngin€eß ¿nd Envimnmenlâl Sdentids TABLE I SUMMARY OF LABORATORY TEST RESULTS l{o. ^'I tütfts['ilORAT¡/I OCÄTI{Ì{sAilPt SOILTYPE l*l PTAStS ¡¡IDEX fæD lf,{coilrnED COIiPRESSrI E STREI{GTH SAHO 0¡l ÞËRCEI{I PÂ$Slr{G ilo. 200$wE UAUDUHff tt6l ORÀ\ÆL t9ôl rñ1 OEPTH ft6t ilAN'RAL rrotsluRE c0t{IEt{I I{ATURAt ORY DEN$il frclt BORIIIG Sandy Clayey Sílt848943.8I Sandy Clayey Silt4.7 1037 Sandy Clayey Silt8699l03.8