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Home My WebLink AboutSubsoil Studyl(t t Xumar & Assoclates, Inc.' Geotechnícal and Materials Engineers and Environmental Scientists ,tn Ëmployce Owned Compony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa.com RECEIVED tcT 2 6 2021 GARFIELD COUNTY COMMUNITY DEVELOPMENT Office Locations: Denver'(IìQ), Parker, Colorado Springs, Fort Collirrs, Glenn'ood Springs, and Sumrnit Coulty, Colorado SUBSOIL STUDY F'OR FOUNDATION DESIGN PROPOSED RESIDENCE LOT E-53, ASPEN GLEN 22 KINGF'ISHER LANE GARX'IELD COUNTY, COLORADO PROJECT NO.20-7-641 NOVEMBER 4, 2020 PREPARED F'OR: JAMES GORNICK BUILDING SPECIALISTS ATTN: JIM GORNICK 1OO5 COOPER AVENUE GLEN\ryOOD SPRTNGS, COLORADO 81601 fieornickl988lÐema TABLE OF'CONTENTS PI'RPOSE AND SCOPE OF STUDY ....... PROPOSED CONSTRUCTION SITE CONDITIONS.. SUBSIDENCE POTENTIAL. FIELD EXPLORATION SUBSURFACE CONDITIONS FO{.INDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS ........,..,........ FOLINDATIONS FOIINDATION AND RETAINING WALLS FLOOR SLABS LINDERDRAIN SYSTEM .....,..,..... SIIRFACE DRAINAGE LIMITATIONS..,.... FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS FIGLIRE 5 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS -l - I a -3- 1 3- -4- -4- -5- -6- -6- -7 - -7 - Kumar & Associates, lnc. @ Project No. 20-7-641 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot E-53, Aspen Glery22 Kingfisher Lane, Garfield County, Colorado. The project site is shown on Figwe 1. 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 James Gornick Building Specialists dated October 23,2020. 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, compressibility or swell 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 recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered- PROPOSED CONSTRUCTION Plans for the proposed residence were being developed at the time of our study. The proposed construction is assumed to generally be a 2-story structwe with attached garage. Ground floors are assumed to be structural over crawlspace or slab-on-grade. 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 location, grading or loading information is significantly different than described, 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 with grades of less lhan 5Yo. Elevation difference across the building area is estimated at Kumar & Associates, lnc. @ Project No.20-7-641 1 around 2 feet. Vegetation consists of grass and weeds. There is an artificial pond just beyond the northeast boundary of the lot. To our knowledge, the pond is constructed with an impervious liner to prevent leakage. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age 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, broad subsidence areas and several sinkholes were observed scattered throughout Aspen Glen, mainly east of the Roaring Fork River. The nearest sinkhole was mapped about 400 feet southwest of Lot E-53 and a broad subsidence area was mapped just north of Lot E-53. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the middle to lower Roaring Fork River valley. Sinkholes were not observed in the immediate area of the subject lot. 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 E-53 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. F'IELD EXPLORATION The field exploration for the project was conducted on October 27,2020. 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-458 drill rig. The borings v/ere logged by a representative of Kumar & Associates. Kumar & Associates, lnc. @ Project No. 20-7-641 -3- Samples of the subsoils were taken withl% 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-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. SUBSURF'ACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils, below a thin topsoil laye¿ consist of relatively dense, silty sandy gravel with cobbles in Boring 1 and very stiff sandy silty clay in Boring 2. Relatively dense, silty sandy gravel with cobbles was encountered in Boring 2 at a depth of lYz feet. The dense gtavel continued down to the maximum drilled depth of \Yz feet in the borings. Drilling in the dense, coarse granular soils was difficult due to cobbles and possible boulders and practical auger drilling refusal was encountered in both borings. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and gradation analyses. Results of a swell-consolidation test performed on a relatively undisturbed drive sample of the clay soils, presented on Figure 4, indicate low compressibility under conditions of light loading and low moisture content with a low hydro- compression potential under a 1,000 psf loading and moderate compressibility after wetting. Results of gradation analyses performed on small diameter drive samples (minus lVz-inch fraction) of the coarse granular subsoils are shown on Figwe 5. The laboratory testing is summarized in Table 1 No free water was encountered in the borings at the time of driliing and the subsoils were slightly moist. F'OUNDATION BEARING C ONDITIONS The natural sandy clay soils encountered at Boring 2 are low density and compressible mainly when wetted. The underlying sandy gravel soils possess moderate bearing capacity and typically low settlement potential. At assumed excavation depths, we expect the subgrade will expose the Kumar & Associates, lnc. o Project No^ 20-7-641 -4^ silty sandy gravel with cobbles. Excavations of less than around 2 feet in depth in clay soils should be deepened to expose the less compressible gravel soils. The sub-excavated depth can be backfilled with structural fill. DESIGN RECOMMENDATIONS FOI.'NDATIONS 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 gtanular soils or compacted structural fill. The design and construction criteria presented below should be observed for a spread footing foundation system. t) Footings placed on the undisturbed natural granular soils or compacted structural frll should be designed for an allowable bearing pressure of 2,500 psf. Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. 2) The footings should have a minimum width of 16 inches for continuous walls and 2 feet for isolated pads. 3) Exterior footings and footings beneath ur¡heated 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 reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12 feet. Foundation walls acting as retaining structures should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section ofthis report. 5) The low-density clay soils, topsoil and any loose 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. Structural fill placed below footing areas should be a relatively well graded granular soil such as'/o-inch road base compacted to at least 98% of Kumar & Associates, lnc. o Project No. 20-7-641 -5- standard Proctor density at near optimum moisture content and extend at least one-half the fill depth below the footing laterally beyond the edges of the footing. A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOT'NDATION AND RETAINING WALLS Foundation walls and retaining stmctures which are laterally supported and can be expected to undergo only a siight 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 granular soils. Cantilevered retaining structures which are separate from the residence and can be expected to deflect sufficiently to mobilize the fuIl 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 glanular soils. Backfill should not contain organics orrock largerthan about 6 inches. All foundation and retaining structwes should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, fraffic, 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 95% of the maxlmum standard Proctor density at a moisture content near optimum. Backfill placed in pavement and walkway areas should be compacted to at least 95% 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 of the footings can be calculated 6) Kumar & Associates, lnc. o Projecl No. 20-7-641 -6- based on a coefficient of friction of 0.50. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 400 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 a granular material compacted to at least 95o/o of the maximum standard Proctor density at a moistu¡e content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, 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 urrestrained 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 than2o/o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% of maxrmum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site granular soils devoid ofvegetation, topsoil and oversized rock. LINDERDRAIN SYSTEM Although free water was not encountered during ow 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, 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 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 sloped at a minimum 1o/o to Kumar & Associates, lnc. @ Project No. 20-7-641 -7 a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain system should contain less than 27o 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 IVz feet deep. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation ofthe foundation excavations and underslab areas shouldbe avoided during construction. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% of the maximum standard Proctor density in pavement and slab areas and to at least 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 6 inches in the first 10 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 finer graded soils to reduce surface \Ã/ater 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 5 feet from foundation walls. 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 Kumar & Associates, lnc. @ Project No. 20-7-641 8- 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 perfonned. If conditions encountered during construction appear different from those described in this report, we should be notified so thal 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 verifo thal the recorrmendations 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 filI by a representative of the geotechnical engineer. Respectfully Submitted, Kumar & Associates, Inc. Steven L. Pawlak, P.E Reviewed by: ç Daniel Hardin, P.E. SLPlkac cc: PatrickStuckey(¡1*ca¡cåi*çorqtia¡t.çc1J {:" (r,15222 t Kumar & Asscciales, lfic, a Projeel lrlo, 20"7'64f BENCHMARK: GROUND SURFACE AT PROPERTY CORNER EL 100,, ASSUMED 50 0 50 100 APPROXIMATE SCALE_FEET 20-7 -641 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. l Ê WC=2.3 +4=52 -200= 1 3 BORING 1 EL. 99.5' B OR NG2 101'EL. 0 0 50/6 s/6, 17 /6 WC=5.9 DD= 1 00FUU L I =F LUÕ 5 5 F Lrl Lll LL I =lfL tr-l 5e/12 7S/12 10 10 LEGEND TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, BROWN CLAY (CL); SILTY, SANDY, VERY STIFF, SLIGHTLY MOIST, BROWN, Iffi CNOVE' AND COBBLES (GM); SILTY, SANDY, PROBABLE BOULDERS, DENSE, LIGHT BROWN TO lH GRAY BRowN. RoUNDED RocK. DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE i DRTVE SAMPLE, 1 S/1-|NCH r.D. SPLIT SPOON STANDARD PENETRATION TEST <n ¡n DRIVE SAMPLE BLOW COUNT. INDICATES THAI 50 BLOWS 0F A 1 40-P0UND HAMMER"", " FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 6 INCHES, I enacrrcal AUcER REFUSAL. NOTES 1 THE EXPLORATORY BORINGS WERE DRILLED ON OCTOBER 27,2O2O 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 MEASURED BY HAND LEVEL AND REFER TO THE BENCHMARK ON FIG. 1. 4, THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DECREE 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 CIRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (Z) (ISTV D2216); DD = DRY DENSITY (PCT) (ISTU D2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM 06913); -2OO= PERCENTAGE PASSING NO.2OO SIEVE (ASTM D1140). 20-7 -641 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 SAMPLE OF: Sondy Sil'ty Cloy FROM:Boring2@1' WC = 5.9 %, DD = 100 pcf in th6 ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WËTTING 2 -J -JLJ> U'' I z.o t- âfo U)zoO -2 -4 -o -8 -10 1.0 ED PRESSURE - KSF 10 Fig.3SWTLL_CONSOLIDATION TEST RESULTSKumar & Associates20-7 -641 EtI 3¡ 45 rì RR 3i :!Ê9 z1 ı too 90 ao 70 60 40 20 to o o 10 20 30 10 60 70 60 90 to0 - .oor .o02 ,oo5 .600 t.: a 152 DIAMETER OF IN MI CLAY TO SILT COBBLES ORAVEL 52 % SAND LIQUID LIMIT SAMPLE 0F: Silly Sondy Grovel 35% PLASTICITY INDEX SILT AND CLAY 13 % FROM: Boring 1 O 2.5' & 5' (Comblnad) lh€3ô l6sl rosulli apply only tó thê sqmpler vhlch w6r6 loslgd. Tha t63llng rèporl shdll nol b¡ roproducod, óxcopl ln full, wlthout th€ wrlllen opÞrovol ol Kumdr & Assoclqtos, lnc' si.vc oñolysls le3llng is pørform€d in occordoncã wlth ASÍM D6913, ÀSTM D7928, ASTM C136 ond/or ASTM 011,(0. SIEVE ANALYSISHYDROMETER ANALYSIS U.S. SÎANDARD SERIES SQUARE OPENINGSTIME Ì ì ! 'iI i rli ¡ ,l1,: I ::: aa I : iLl,,,rl GRAVELSAND MEDIUM COARSE FINE COARSEFIN E 20-7 -641 Kumar & Associates GRADATION TEST RTSULTS Fig.4 lGttH,tiåffiffii'iÍå*"TABLE 1SUMMARY OF LABORATORY TEST RESULTSSOILTYPESílty Sandy Gravel13Sandy Silty ClayfosflUNCONFINEDCOMPRESSTVESTRENGTHPLASTICINDEX{o/"\ATTERBERG LII\IIITSt%lLISUID LIMITPERCENTPASSING NO.200 stEvESANDti/"|35GRADATION(%)GRAVEL52100NATURALDRYDFNSIWlncfl{%tNATUR.A,LMOISTURECONTENT2.3s.92%and5combined1lftìDEPTHSAMPLE TOCATIONBORING12No.20-7'641