The URL can be used to link to this page

Home My WebLink AboutSubsoil Studyrc,I Kumar & Associates, lnc.' Geotechnical and Materials Engineers and Environmental Scientists An Employcc Ownsd Company 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com www.kumarusa.com Ofäce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado RECEIVED ÅUË 2 4 2Û?2 GARF]ELD COUNTY COMMUNITY DEVELOPMENT SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT SD-16, ASPEN GLEN SUNDANCE TRAIL GARFIELD COUNTY, COLORADO PROJECT NO.21-7-904 JANUARY 26,2022 PREPARED FOR: JORDAN ARCHITECTURE ATTN: BRAD JORDAN P.O. BOX 1031 GLEI\WOOD SPRTNGS, COLORADO 81602 brad i ordanarchitect@ gmail.com TABÞE qF PONTENTS PTTRPOSE ANÐ SCOPE OF STUDY PROPOSED çQNqTRUCTION -i SITE CONDTTIONS I .L . SUBSIDENCE POTENTIAL t: \ SUBSURFACE, PqNDTTIONS :' FOUNDATION HPARING CONDITIONS DESIGN ATIONS FOUNDA FLOOR S IINDERDRAIN S YSTEM SURFACE DMTN AGE LIMITATIONS FIGURE I . LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS I I I a -) - J J- ..............¡ J J 4 5 5 -6- FIGURE 5 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, lnc. @ Project No. 21-7-994 PTJRPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot SD-16, Aspen Glen, Garfield 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 proposal for geotechnical engineering services to Jordan Architecture dated November 23, 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 freld 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 proþosed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION Plans for the proposed residence were conceptual at the time of our study. The proposed residence will likely be a two-story structure with attached garage. Ground floor could be structural over crawlspace or slab-on-grade. Grading for the structure 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 subject site was vacant and covered with about 3 inches of snow at the time of our field exploration. The temain is relatively flat near the front of the lot, gently sloping down to the southwest across the center of the lot and steeper down to the northeast at the rear of the lot. A dry drainage ditch is at the rear of the lot. Vegetation consists of grass and weeds with scattered bushes. Kumar & Associates, lnc. @ Project No. 21-7-904 .l $UBSID&NÇF FOTBISTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporitc undcrlics thc Aspon Glcn Subdivision These rocks are a sequence of gypsiferous sh4le, frne-grained sqndstone an{ siltstone with some massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits associated with the Eagle Valley p,vaporite underlie portions of the lot. Dissolution of the gypsum under çertain conditions ppn cause sinkholps to develop : I .. and can produce areas of localized subsidence. During previous work in the area, several sinkholes were obseryed scattered throughout Aspen Glen, mainly east of the Roaring Fqrk River. A small sinkhole was mapped about 575 feet northwest of Lot SD-16, under the pond to thg northwest. These sinkholes appear similar to others associated with the Eagle Valley -Erraporite 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, tor f-oundation 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-16 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 December 10,2021. Two exploratory borings were drilled at the locations shoWn on Figure I tb evaluate the subsurface conditions. The borings were 4dvanced with 4-inch diameter continuous flight augers powered by a truck- mounted CME-458 drill rig. The borings were logged by a representative of Kumar & Associates, Inc. Samples of the subsoils were taken with l%-inch and 2-inch I.D. spoon samplers. The samplers were driven into the subsoils at various depths with blows from a 14O-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 ret¡rrned to our laboratory for review by the project engineer and testing. Kumar & Associates, lnc. @ Project No. 21-7-904 -J- SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils encountered, below about Yzto 1 foot oftopsoil, consist ofabout 2Yzto3%feet ofvery stiff, sandy clay overlying dense, silty sandy gravel with cobbles and probable boulders down to the maximum explored depth of 1l feet. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and gradation analyses. Results of swell-consolidation testing performed on a relatively undisturbed drive sample of the sandy clay, presented on Figure 4, indicate low to moderate compressibility under conditions of loading and wetting. Results of gradation analyses performed on small diameter drive samples (minus lYz-inch fraction) of the coarse granular subsoils are shown on Figure 5. The laboratory testing is summarizedin Table l. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist. F.oUNuatTON nnahTNG CoNDITIoNS The upper sandy clay soils possess low bearing capacity and low to moderate settlement potential. The natural sandy gravel soils possess moderate bearing capacity and typically low settlement potential. At assumed excavation depths we expect the subgrade will expose the sandy gravel soils. Shallow excavation areas or slab-on-grade areas may expose the upper sandy clay soils. Footing areas that expose clay soils should be deepened to expose natural granular soils. The sub-excavated depth can be backfilled with the onsite granular soils excluding rocks larger than 6 inches. Spread footings placed on natural granular soils or compacted structural fill should be feasible for foundation support of the residence with a low risk of settlement. DESIGN RECOMMENDATIONS FOUNDATIONS 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 or structural fill compacted to at least 98% of standard Proctor density. The design and construction criteria presented below should be observed for a spread footing foundation system. Kumar & Associates, lnc. @ Project No. 21-7-904 -+- 2) 1) 3) 4) f'ootings placed orl the undisfrtrbeÉl 44{ural granr4lar soils or strupturral fill shoulfl be designed for an allowable bparing pressure of 3,000 psf. þ4sed on experie¡pe, we expect settlement of footings dosigned and cqnstructed 4s disçussÊd in this scction will be abqut I inch or less. ' Tþe footings should have a mipimqm width of l6 inches for oo4fi¡ggpswalls and 2 feet for isolaiecl pacls. Exterior footings and footings beneath unheated areas should be.provided with ¿dequato soil cover above their bearing elevation for frost protecfipn. Placemenf of foundations at least 36 inches below exterior grade is typicalfy fQpd in this arga. l'' I : 'l : , j . Ì .ì Continuous foundation walls should be reinforced top and bqffglp ffl span local anomalies such as by assuming an unsupported length of at leasf f 2 feet. Foundation walls 4cting as retaining structures should also bp {psig¡ed to resist a lateral earth pressure torresponcling to an equivalent fluid unit weigþf of at least 4i pcf for the onsite granular soil as backfill. Topsoil,,sandy clay and any loose disturbed soils should be remqvgd 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 exqavations prior to concrete placement to evaluate bearing conditions. s) 6) 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 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 than2Yopassing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 957o of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on-site granular soils devoid of vegetation, topsoil and oversized rock. Kumar & Associates, lnc. @ Project No. 21-7-904 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, 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 1 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 2%o passing the No. 200 sieve, less than 50olo passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least lYz 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 95%o 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 suruounding 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 l0 feet in unpaved areas and a minimum slope of 3 inches in the first l0 feet in paved areas. Free-draining wall backflrll should be covered with filter fabric and capped with about 2 feeÍ. 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 imigation should be located at least 5 feet from foundation walls. Kumar & Associates, lnc. @ Project No, 21-7-904 -6- LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area atthis time. We make no warranty either express or implied. Thc conclusions and recorffnendations submitted in this repofi are based upon the data obtainetl 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 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 pre,pared for the exclusive use by our client for design purposes. Vy'e 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 rnodifications to the recomnendations 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. Respectfu lly Submitted, Ku¡¡rar & ,4ssociateso Ine- James H. Parsons, P Reviewed by: ffi*,/- Steven L. Pawlak, P.E. JHP/kac Kumar & Assoeiat*s, lnc. í'Project No. 21"7"9t4 . .,...,,\1 : ', t:lÀ LOT SD-15 OBORING 1 oBoRtNç..t2 LOT SD-16 2002040 APPROXIMATE SCALE-FEET 21 -7 -904 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 7 BORING 1 BORING 2 0 0 16/12 WC=6.8 DD-99 1 4/12 WC=10.8 -200=90 5 F- t¡J l¡JtL I-t'-È t¡Jo so/3 1 /6, 50/4 t-LI L¡l LL I-l-o- LrJo 10 1050/ 4.5 50/4 ì Èl: 15 15 r9 f,; !t3 WC= 1 .8 +4=46 -200=1 6 21 -7 -904 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 '? ¡ I I Ê h LEGEND N TOPSOIL: CLAY, SANDY TO VERY SANDY, SILTY, FIRM, MOIST, DARK BROWN. CLAY (CL); SANDY TO VERY SANDY, SCATTERED GRAVEL, SLIGHTLY CALCAREOUS, SLIGHTLY POROUS, VERY STIFF, SLIGHTLY MOIST, BROWN. l:' :z I r;'.:)tzl GRAVEL DENSE, (GM-GP): SANDY, COBBLES, SLIGHTLY SILTY TO SILTY, PROBABLE SMALL BOULDERS, SLIGHTLY MOIST, GRAY AND BROWN. DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE I DRTVE SAMPLE, 1 S/9-|NCH r.D. SPL|T SPoON STANDARD PENETRAT|oN TEST. 1^/1t DRIVE SAMPLE BLOW COUNT. INDICATES THAT 16 BLOWS OF A 14O-POUND HAMMER'",.. FALLING 30 INCHES WERE REQUIRED To DRIVE THE SAMPLER 12 INCHES. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON DECEMBER 10, 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. 5. 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 GONTENT (%) (ASTM D2216); DD = DRY DENSTTY (pcr) (lSrU Ð2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM 06913); -2oQ= PERCENTAGE PASSING N0. 200 SIEVE (ASTM 01140). 21 -7 -904 Kumar & Associates LEGEND AND NOTES Fig. 3 1 0 JJ l.¡l =UI I z.o F ô Jo UIz.oo 1 -2 -5 -4 -5 -6 -7 -8 1 1.0 APPLIED PRESSURE - KSF 10 SAMPLE OF: Sondy Cloy FROM:Boringl@2.5' WC = 6.8 %, DÐ = 99 pcf ln oñd Aaaoc¡otè, lnc. ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 21 -7 -904 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4 I E HYDROMETER ANALYSIS SIEVE ANALYSIS fIUE RUDINGS ¿4 HRS 7 HRS Ð ¡t oo U.S. STANDARD SERIES 450 ¡¿o tlo ¡t6 ¡tô ¡â CLEAR SOUARE OPENINGS a/À' 1/L' t t/.' / I i i I I =e E too 90 ao 70 60 30 ao 30 20 to o o lo 20 JO 40 50 50 70 80 90 r00 = 1,75 9.5 t9 5A.t -125 i52 CLAY TO SILT COBBLES GRAVEL 46 % SAND LIQUID LIMIT SAMPLE OF: Very Sondy Silly Grovel 38%SILT AND CLAY 16 % PLASTICITY INDEX FROM: Bor¡ng 1 e 5' & 10' Combined The3o l6sl roeults qpply only lo the somplos which w€re lesled. Th. l€sllng roporl sholl nol bo roproducod, oxcopl ln full, wllhoul lhe wrlll€n opprovol of Kumor & Assgclqlgs, lnc. Sl€v€ onoly3ls ldsllng ls p6rfo.m6d ln occordonco wlth ASTM D69í3, ASTM D7928,Asfll C156 ond/or ASTH Dll.l0. SAND GRAVEL FINE MEDTUM ICOARSE FINE COARSE 21 -7 -904 Kumar & Associates GRADATION TEST RESULTS Fig. 5 lGrtå#ni#.trniÏiå**TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.21-7-9042Iæffie2%5& 1ûCombined2Y2OEPIHsålPtE LocATlolt ..)10.81.86.8lo/"1¡¡¡iunEt-'MOISTUREGO|WEtg99focflDRYDENSITY. NAÎURAL46(/"1GRAVELGRADi38(f/"1SAND90I6PERC€NTPASSING NO.200 srEVELIQUID LIMITIolollo/olPLASTICINDEXlosflUNCONFINEDCOMPRESSIVESTRENGTHSlightly Sandy ClayVery Sandy Silty GravelSandy ClaySOIL TYPE