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Home My WebLink AboutSubsoil Study for Foundation Design 02.06.2021Ktf l(umar & Assoclatc, lno.@ Geotechnical and Materials Engineers and Environmental Scientists An Emfloyca Ownod Comgrny 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970)945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com 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 SD-12, ASPEN GLEN SUNDANCE TRAIL GARFTELD COUNTY, COLORADO PROJECT NO.21-7-131 FEBRUARY 6,2021 PREPARED FOR: KEVIN YOX P.O. BOX 181631 DENVER, COLORADO 81623 @ TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS SUBSIDENCE POTENTIAL FIELD EXPLORATION SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS .. DESIGN RECOMMENDATIONS FOUNDATIONS FLOOR SLABS..... UNDERDRAIN SYSTEM .......... SURFACE DRAINAGE.............. LIMITATIONS FIGURE I - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGIIRE 3 - LEGEND AND NOTES FIGURE 4 - GRADATION TEST RESULTS TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS l- 1 -2- ..-2- a-J- J. J J 4 5 5 5 Kumar & Associates, lnc. @ Project No.21-7-131 PURPOSE AND SCOPE OF STUDY This report presents the results ofa subsoil study for a proposed residence to be located on Lot SD-12, Aspen Glen, Sundance Trail, 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 accordance with our proposal for geotechnical engineering services to Kevin Yox, dated January 14,2021. A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils obtained during the field exploration were tested in the laboratory to determine their classification and other engineering characteristics. The results of the field 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 conclusions, design recofilmendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The proposed construction will be a 2-story wood frame residence over a crawlspace with an attached garuge with slab-on-grade floor. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 5 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building locations, grading, or loading information change significantly from those described above, we should be notified to re-evaluate the recommendations presented in this report. SITE CONDITIONS The subject site was vacant at the time of our field exploration. The ground surface is relatively flat and nearly level to gently sloping down to the northwest. There were patches of snow 3 to 4 inches deep on portions of the lot. Elevation difference across the building area is estimated at around I to 2 feet. Vegetation consists of grass and weeds. There is an artificial pond on the northwest boundary of the lot. To our knowledge, the pond is constructed with an impervious liner to prevent leakage. Kumar & Associates, Inc. @ Project No.21-7-131 .| SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanianage Eagle Valley Evaporite underlies the Aspen Glen Subdivision. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the area, several sinkholes were observed scattered throughout Aspen Glen, mainly east of the Roaring Fork River. A small sinkhole was mapped about 150 feet northwest of Lot SD-12, under the pond that borders the lot on the northwest side. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the middle to lower Roaring Fork River valley. No evidence of cavities was encountered in the subsurface materials; however, the exploratory borings were relatively shallow, for foundation design only. Based on our present knowledge of the subsurface conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of future ground subsidence on Lot SD-12 throughout the service life of the proposed residence, in our opinion, is low; however, the owner should be made aware of the potential for sinkhole development. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. FIELD EXPLORATION The field exploration for the project was conducted on January 25,2021. 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 a l3A-inch I.D. spoon sampler. The sampler was 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 Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. Kumar & Associates, lnc. @ Project No. 21-7-131 J SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. In Boring 1, beneath about I foot of topsoil, the subsoils consist of about I foot of stiff, silty sandy clay overlying relatively dense silty sand and gravel with cobbles and possible boulders down to the drilled depth of 11 feet. In Boring 2,beneath about I foot of topsoil, relatively dense silty sand and gravel with cobbles and possible boulders was encountered down to the maximum drilled depth of 9 feet. Drilling in the dense, coarse granular soils was difficult due to cobbles and possible boulders and drilling refusal was encountered in both borings. Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of gradation analyses performed on small diameter drive samples (minus \%-inch fraction) of the coarse granular subsoils are shown on Figure 4. The laboratory testing is summarizedin Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The natural sand and gravel soils possess moderate bearing capacity and typically low settlement potential. At assumed excavation depths we expect the subgrade will expose the sand and gravel soils. Spread footings should be feasible for foundation support of the residence with a low risk of settlement. DESIGN RECOMMENDATIONS FOLINDATIONS 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 granular soils. The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed on the undisturbed natural granular soils should be designed for an allowable bearing pressure of 3,000 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about I inch or less. Kumar & Associates, lnc. @ Project No.21-7-131 2) -4- The footings should have a minimum width of 16 inches for continuous walls and 2 feeI" for isolated pads. 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. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls and retaining structures which arelaterally 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 45 pcf for backfill consisting of the on-site granular soils. The topsoil, low-density clay and silt soils, and any loose or disturbed soils should be removed and the footing bearing level extended down to the relatively dense natural granular soils. The exposed soils in footing area should then be moistened and compacted. A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. 3) 4) FLOOR SLABS The natural on-site coarse granular soils are suitable to support lightly loaded slab-on-grade construction. 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 interior slabs-on-grade for support. This material should consist of minus 2-inchaggregate with at least 50% retained on the No. 4 sieve and less than 12% passing the No. 200 sieve. All filImaterials for support of floor slabs should be compacted to at least 95"/o of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site coarse granular soils devoid of vegetation, topsoil, and oversized rock. 5) 6) Kumar & Associates, lnc. @ Project No.21-7-131 5 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. We recommend below-grade construction, such as retaining walls and crawlspace 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 lYo to a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain system should contain less than 2o/opassingthe 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 l%feet deep. SURFACE DRAINAGE 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. 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 90o/o 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 6 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 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 all backfill. 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. Kumar & Associates, lnc. @ Project No.21-7-131 -6- The conclusions and recornmendations submitted in this report are based upon the data obtained from the exploratory borings drilled at the locations indicated on Figure l, the proposed type of construction and our experience in the area. Our services do not include determining the presence, preventiono 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 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 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 verifu that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recoilrmendations presented herein. We recommend on-site observation of excavations and foundation bearing strata and testing of structural fillby a representative of the geotechnical engineer. Respectfully Submitted, Kumar & Associateso Inc. David A. Noteboom, Staff Engineer Reviewed by: Daniel E. DEH/kac Kumar & Associates, lnc. o Project No.21-7-131 i : !\, lb'fe"rc"g ., vtJ /a I i\%.l\--li'l' \r 1r --,t+- lrs/ d -vrt' "ru\ \ ftrs. .f \ lr:f tZ/ . {. toi.so,-' *S 3/";o;ie" tr -(: - \ 7.5'Drolnoge PurpososI \ 1 & rof tz? - \Droinoge lrrigqilon i 1 - \\..r' 7.5'Ullllty, Drqlnog6 & lrrlgqtion Puaposes Eosement { \ 1 4'r---u r$ L aa t\ / .aJLt*' /,f L-p Droinoge lrrigolion and,r ,fo- /2 \ ,rt, +-,t!l 23,634. sq.ft. 0.54 dcres 8a, .$7J BORING 2 tility, Dralnoge olion Purposes :osement &\ap a DrqlncAe lrriqotlon ond -uEos€m€nt 0 ,gp* / /!\ Y4.". \.- 20 APPROXIMATE SCALE_FEET 21 -7 -131 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING 1 EL. 6073' BORING 2 EL. 6072' 0 0 25/6, 50/1 WC=5.8 -200=58 37 /6, so/3.5 5 46/12 WC=1.9 *4=39 -200= 1 5 40/6, 51 /6 5 F LJ trJI! ITF(L LrJo 34/6, sO/3 so/3 FLItrll,! I-F(L tdo 10 10 so/1.5 15 15 WC=2.5 +4=46 -2QQ=20 21 -7 -131 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND TOPSOIL; SANDY CLAY, ROOTS AND ORGANICS' FIRM, SLIGHTLY MOIST, BROWN. CLAY (CL); SILTY, SANDY TO VERY SANDY, STIFF TO HARD, SLIGHTLY MOIST, BROWN GRAVEL AND SAND (GM-SM); SILTY, WITH COBBLES AND PROBABLE SMALL BOULDERS, VERY DENSE, SLIGHTLY MOIST, MIXED BROWNS. GRAVEL BOULDE (0v); RS, VE SANDY TO VERY SANDY. SILTY, WITH COBBLES AND PROBABLE SMALL RY DENSE, SLIGHTLY MOIST, BROWN. I DRTVE SAMPLE, 1 S/1-|NCH l.D. SPLIr SPOON STANDARD PENETRATION TEST c<ze DRIVE SAMPLE BLOW COUNT. INDICATES THAT 25 BLOWS OF A 140-P0UND HAMMER'"/ " FALLTNG so tNcHES WERE REeUIRED To DRtvE THE SAMPLER 6 tNcHES. f enncncAl AUGER DRTLLTNG REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 25, 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 OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS 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); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (NSTU OOSIS); -20o= PERCENTAGE PASSING NO. 200 SIEVE (ASTM Dl140). 21 -7 -131 Kumar & Associates LEGEND AND NOTES Fig. 3b I 2 a , to0 g0 ao 70 60 50 B g0 20 to o 0 to 20 30 40 50 80 70 ao 00 too =E E P H I OF IN MI CLAY TO SILT COBBLES GRAVEL 39 % SAND LIQUID LIMIT SAMPLE OF: Sllty Sond ond Grovel 46% PLASTICITY INDEX SILT AND CI-AY 15 % FROM:BorlnglO4' HYDROMETER ANALYSIS SIEVE ANALYSIS IIYE READINCS a6utx rcutN aulNl,l HRS 7 HRS rvtN at U.S. STANDARD SERIES CLEAR SQUARE OPENINGS ttu. tt^. t ttt. t a E lo0 so ao 70 60 50 ao 30 20 to o o 10 20 30 ,l{l 50 60 70 ao 90 100 E ts DIAMETER OF PA CLAY TO SILT COBBLES GRAVEL 46 % SAND LIQUID LIMIT SAMPLE OF: Sllly Sondy Grovel 31 % PLASTICITY INDEX SILT AND CLAY 20 % FROM: Borlng 2 O 2' &.4' (Comblned) Th.tr l.tl rorullr opply only lo lhc rqmplar whlch v!r. b!bd, Th. t.tllng r.porl lholl nol b. r6produc.d, rxq.pl ln full wllhout lhe wrliionqpprcvol ol Kumqr I Alroclqlcr, lnc, Slcvc onolyrh icdlng h pcrfomcd ln occordoncc wnh ASTI, D6913, ASTM D7928, ASTM C155 qnd/or ASTM Dt1,t0, SIEVE ANALYSISHYDROMETER ANALYSIS CLEAR SOUARE OPENINOSNTE REAOINOS 24 HRS 7 HRS rlttr at * * - - * 4- - - - - - - *t - - - t " - - 4- - - - - * * - - /- t -*- - - - ^ GRAVELSAND FINE MEDTUM ICOARSE FINE COARSE SAND GRAVEL FINE MEDIUM COARSE FINE COARSE 21 -7 -131 Kumar & Associates GRADATION TEST RESULTS Fig. 4 l(J_Afl3ffi ,l:ffiftrtrn[i3;,,*-, TABLE 1 SUMMARY OF LABORATORY TEST RESULTS I BORING 2 2 and4 combined 4 I {ft) DEPTH SAMPLE LOCATION 2.3 1 9 5.8 l:/") GRAVEL $t SAND NATURAL MOISTURE CONTENT NATURAL DRY DENSITY PERCENT PASSING NO. 200 stEVE 46 39 34 46 20 1 5 58 Silty Sandy Gravel Silty Sand and Gravel Silty Sandy Clay SOIL TYPE ATTERBERG LIMITS LIQUID LIMIT UNCONFINED COMPRESSIVE STRENGTH PLASTIC INDEX No.21-7-131