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HomeMy WebLinkAboutSubsoils Report for Foundation DesignlGrtU*l*Oiggsf*i-.''5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com An Employcc Orncd Compony www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 4, RIVER VIEW RANCH SUBDIVISION 243 SHORE DRIVE GARFIELD COUNTY, COLORADO PROJECT NO.24-7-660 DECEMBER30,2024 PREPARED FOR: wooDSToNE,INC. ATTN: ALAN SHORT 263 LEWIS LANE BASALT, COLORADO 8162I Alan@woodstonein c.net TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS FIELD EXPLORATION SUBSURFACE CONDITIONS FOI.INDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS ............ FOI-INDATIONS FOLINDATION AND RETAINING WALLS ..... FLOOR SLABS IINDERDRAIN SYSTEM SURFACE DRAINAGE LIMITATIONS.......... FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 through 6 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESIILTS 1 1 1 1 a ....- 2 - 2 2 aJ 4 4 5 -5- Kumar & Associates, lnc. @ Project No.2'l-7-660 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 4, River View Ranch Subdivision,243 Shore Drive, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for the foundation design. The study was conducted in general accordance with our agreement for geotechnical engineering services to Woodstone, Inc. dated November 13,2024. A field exploration program consisting of exploratory borings was conducted to obtain infonnation on the 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 analyzedto 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 CONSTRUCTION The proposed residence will be a one- or two-story wood-frame structure with an attached garuge with a detached secondary residence located as shown on Figure 1. Ground floors will be slab- on-grade or structural above crawlspace. Grading for the strucfures is assumed to be relatively minor with cut depths between about 2 to 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 recommendations contained in this report. SITE CONDITIONS The building site was vacant at the time of our field exploration. The driveway access is off Shore Drive which crosses the upper part of the lot. The ground surface through the building area is gently sloping down to the northeast. The Colorado River borders the lot to the nor1h. Vegetation through the building area consists of sparse grass and weeds. F'IELD EXPLORATION The field exploration for the project was conducted on December 17, 2024. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 4-inch diameter continuous flight augers powered by a truck-mounted CME-45B drill rig. The borings were 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 Kumar & Associates, lnc. @ Project No. 24-7-660 a 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 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 subsurface profile encountered in the borings consists of very stiff, slightly clayey, slightly sandy to sandy silt down to the maximum depth drilled of about 25 to 30 feet. Laboratory testing perfonned on samples obtained from the borings included natural moisture content and density, and finer than sand size gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed drive samples of the silt soils, presented on Figures 4 and 5, indicate low to moderate compressibility under natural low moisture content and light loading. The samples showed a moderate hydrocompression potential when wetted under light load and moderate compressibility under additional loading after wetting. The laboratory testing is summarized tnTable 1. No free water was encountered in the borings at the time of drilling and the subsoils were typically slightly moist. FOUNDATION BEARING CONDITIONS The silt soils have low bearing capacity and generally moderate compressibility potential under loading. Shallow spread footings placed on the natural soils can be used for foundation support with a risk of settlement and distress mainly if the bearing soils are wetted. A lower risk of settlement fill. -_-t would be to place the ona 3 to 4 feet of compacted structural DESIGN RECOMMENDATIONS FOUNDATiONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, the building can be founded with spread footings bearing on the natural soils with a risk of settlement and distress. Precautions should be taken to prevent wetting of the bearing soils. To reduce the risk of settlement, 3 feet of compacted structural fill consisting of 3/+ inch aggregate case course compacted to at least 98 percent of the maximum standard Proctor density at a moisture content within 2 percent of optimum could be placed beneath footings. The design and construction criteria presented below should be observed for a spread footing foundation system. Kumar & Associates, lnc. @ Project No. 24-7-660 -3 - 1) Footings placed on the undisturbed natural soils or compacted structural fill should be designedforanallowableb@Basedonexperience'weexpect initial settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. Additional differential settlement of around 1 to 2 inches could occur depending on the depth and extent of future wetting. 2) The footings should have a minimum width of 20 inches for continuous wall and 2 feet for isolated columns. 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 area. 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 and built in a box- like configuration. Foundation walls acting as retaining structures should also be designed to resist lateral eafih pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) The topsoil and any loose disturbed soils should be removed in the footing areas. The exposed soils should then be moistened and compacted. 6) A representative ofthe geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOLINDATION 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 55 pcf for backfill consisting of the on- site soils. Cantilevered retaining strucfures which are separate from the residence 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 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 ahorizontal 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 near optimum moisture content. Backfill placed in pavement and walkway areas should be compacted to at least 95%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 Tateral pressure on the wall. Some settlement of deep foundation wall backfill should Kumar & Associates, lnc. @ Project No. 24-7-660 -4- be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. Backfill should not contain organics, debris or rocks larger than about 6 inches. 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 of the footings can be calculated 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 fluid unit weight of 325 pcf. The coefficient of friction and passive pressure values recommended above assume 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 against the sides of the footings to resist lateral loads should be compacted to at least 95o/o of the maximum standard Proctor density at a moisfure content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab-on-grade construction with a risk of settlement like that for footing foundations. 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-rnch 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 50Yo retained on the No. 4 sieve and less than 2%o passing the No. 200 sieve. The garage slab should be underlainby 4 inches of road base. All filI materials for support of floor slabs should be compacted to at least 95oh of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the onsite soils devoid of vegetation, topsoil and oversized rock. LINDERDRAIN 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 also create a perched condition. We recommend below-grade construction, such as retaining walls and basement areas, be protected fiom wetting and hydrostatic pressure buildup by an underdrain system. If a shallow crawlspace is used (and around the garage), an underdrain should not be provided to help keep the shallow footings dry. The drains should consist of 4-inch diameter perforated PVC pipe placed in the bottorn of the wall backfill surounded 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 Kumar & Associates, lnc. @ Project No. 24-7-660 -5- sloped at a minimum %o/o to a suitable gravrty outlet. Free-draining granular material used in the underdrain system should contain less than 2oh passing the 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 llz feet deep. An impervious membrane such as 20 mrl 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 Development of proper surface grading and drainage will be critical to keeping the bearing soils dry and limiting building movement and distress throughout the building life. 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. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95o/o of the maximum standard Proctor density in pavement and slab areas and to at least 90Yo 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 10 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 at least2 feet of the on-site soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of allbackfill. 5) Landscaping which requires regular heavy inigation 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, 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 rvarranty 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 concemed 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 borings and variations in the subsurface conditions may not become evident until excavation is perforrned, If conditions encountered during construction appeffi different from those described in this report, we should be notified so that re-evaluation of the recommendations may be made. Kumar & Associates, lnc. @ Project No. 24-7-660 -6- 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 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 ofstructural fill by a representative ofthe geotechnical engineer. Respectfu lly Submitted, Kumar & Associates, Robert L. Duran, P Reviewed by: b I Daniel E. Hardin, P.E. RLD/kac Kumar & Associates, lnc. o Project No. 24-7-660 Jno*.fg".- - -t II EAqq'qELl!-E I --r- I o I I I I I I I I I l ! I t -t I I 50 uqw I fId w I 9-10 i r('rlq.i l1ir, ,r (tr()ii.liil{ir i , , tr, ., i) APPROXIMATE SCALE-FEET LOCATION OF EXPLORATORY BORINGS Fig. 124-7 -660 Kumar & Associates BORING 1 BORING 2 0 0 12/12 WC=9.2 DD=97 20/ 12 5 1o/12 16/ 12 WC=7.8 DD=98 -2QO=7 4 5 10 17 /12 WC=5.5 DD=97 -2OO=72 13/12 WC=5.0 DD= 1 0B -200=50 10 FulLj LL I-F(L tr.lo 15 1s/12 WC=5.7 DD= 1 02 -200=85 1s/12 WC=6.2 DD= 1 06 15 FtrltJtL I :EFo-L!o 20 18/ 12 20 25 18/ 12 25 30 18/ 12 30 24-7 -660 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND TOPSOIL; SANDY SILT, SLIGHTLY CLAYEY, FIRM, MOIST, BROWN, ORGANIC. 7'," (UI-); SANOY TO VERY SANDY, SLIGHTLY CLAYEY, STIFF TO VERY STIFF, SLIGHTLY MOIST lzro Motsr, LTGHT BRowN To BRowN. DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE i DR|VE SAMPLE, 1 S/3-INCH t.D. SPLTT SPOON STANDARD PENETRATTON TEST. 12117 DRIYE SAMPLE BLOW COUNT. INDICATES THAT 12 BLOWS OF A 14O-POUND HAMMER'-l'- FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. _+ DEPTH AT WHICH BORING CAVED FOLLOWING DRILLING. NOTES 1 THE EXPLORATORY BORINGS WERE DRILLED ON DECEMBER 1 7, 2024 WIIH 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 OF THE EXPLORATORY BORINGS ARE PLOTTED TO DEPTH. 4. THE 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 THE 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 (pcf) (ASTM D2216); -2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1140). -e 24-7 -660 Kumar & Associates LEGEND AND NOTES Fig. 3 SAMPLE OF: Sondy Silt FROM:Boringl@2' WC = 9.2 %, DD = 97 pcf I I --.1 I ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING i I l j I I I l i I I i i I Bholl not ln D-6ffi. br 2 JJ LrJ =a I z.otr o =o U1zoo 0 -2 -4 -6 -8 -10 -12 1.0 24-7 -660 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4 CoNSoLTDATTON - SWELL (%) I @ I N I o I o) I ts IN o N !!trn0 Tnraacvr I xo o oo t<na863=o"<t- ll(Jt(Drrl {i.n!oN .' .'.1o\ (o }R ogo@-d il (oa(o-={ Eo cz.>00r|1EI oF= Fs9,2.>oqr €=8n-r< )x# "nQ c(JVZ.m 8I5_=e3 3iii *.1*3 *EF*r FE o44. X =E 5i4#e *9i€ *,i ceigig*; +6 N5 I! I o)o)O xc 3 0)a Po @ @oo. 0) oa a€rrlt-t- I C)oz.aot- tr -{Oz. -lrrla -.t nrnaCI_ -.{a =I ('| 5 6o- -@-o9_c-oo)tn ll b".ro 5;;3 urco'ollJ(L> 3 E e T ul7E ^lYu1 Eflo L'J e. Z.Fo-= .AFIJ 8== L'aP<2.- 68sEouo OllJoo<2. f I - ---- \ __-] _ 9* ilEE !;6i'sP"ET iE Fl sl-El ;eEt€s6it F.: fi.Es9g ra _ t 9-t50;= .+c::=E o N I { I (o I @ I o I N I N (z) -t-n/ts NOllvonosNoS o(o(o IF\ I{N ao (o'6 oaa od L G Ef,Y aFJ =at! E. Fa l-dF z.O F o =O U)z.O(J IJJ Llt =(n (o C',i; ol udlzzo - gzoz I(tAf''ffil:iffi*#:*ii$-'" TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 24-7-660 2 1 BORING SAMPLE LOCATION 1 4 9 4 1 4 9 2 DEPTH {ft) 6.2 s.0 7.8 5.7 5.5 9.2 NATURAL MOISTURE CONTENT lol 106 108 98 t02 97 97 NATURAL DRY DENSITY Iocfl GRAVEL (%) GMDATION SAND %l 50 74 8s 72 ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH PERCENT PASSING NO. 200 stEVE PLASTIC INDEXLIQUID LIMIT SOIL TYPE Sandy Silt Very Sandy Silt Sandy Silt Sandy Silt Sandy Silt Sandy Silt