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Home My WebLink AboutSubsoil StudyICrtiiffi fi*är:Ë:if '!nÊ;;'*^ An Employcc Owncd Compony 5020 County Road 154 Glenwood Springs, CO 8 160 I 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 RECEIVED .4{.'{ì fi 2 ?.{}??. gîfr,iJFil,fi?#il.li SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 390 PHASE 3, TRONBRTDGE BLUE HERON DRIVE GARFIELD COUNTY, COLORADO PROJECT NO. 21-7-435 JULY 8,2021 PREPARED FOR: SCIBO LLC ATTN: LUKE GOSDA 0115 BOOMERANG ROAD, SUrTE 52018 ASPEN, COLORADO 81601 lu ke.gosda@sunriseco.com TABLE OF CONTENTS PIJRPOSE AND SCOPE OF STI"IDY...... PROPOSED CONSTRUCTION SITE CONDITIONS..... GEOLOGY FIELD EXPLORATION SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS .. DESIGN RECOMMENDATIONS ........ FOUNDATIONS FLOOR SLABS UNDERDRAIN SYSTEM... SURFACE DRAINAGD............... LIMITATIONS. FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS FIGURE 5 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS 1 -1 1 a -3 - 3- 4 4 5 5 6 .-6- 1 Kumar & Associates, lnc. @ Project No. 2l-7-435 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot39, Phase 3, Ironbridge, Blue Heron 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 accordance with our agreement for geotechnical engineering services to SCIB, LLC dated May 10, 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 f,teld 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 At the time of our study, design plans for the residence had not been developed. The building is proposed within the upper part of the building envelope shown on Figure 1. For the purposes of our analysis, we assume the proposed residence will be a wood frame structure over a crawlspace with an afÍached slab-on-grade garage. Grading for the structure is assumed to be relatively minor with cut depths between about 2 to 3 feet. V/e 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 at the time of our field exploration. The ground surface is gently sloping down to the north in the proposed building area with a steep slope down to the rear (north side) of the lot at a grade of approximately 30 percent. Vegetation consists of sparse grass and weeds. The downhill side of Blue Heron Drive appears to be a fill bench for residence Kumar & Associates, lnc. o Project No.2l-7-435 "| construction placed during the subdivision dcvclopmcnt. Thc Roaring Fork Rivcr is locatcd downhill about Vomile to the north. GEOLOGY The geologic conditions were described in a previous report conducted for planning and preliminary design of the overall subdivision development by Hepworth-Pawlak Geotechnical (now Kumar & Associates) dated October 29,1997, Job No. I91 327. The natural soils on the lot mainly consist of sandy silt and clay alluvial fan deposits overlying gravel terrace alluvium of the Roaring Fork River. The river alluvium is mainly a clast-supported deposit of rounded gravel, cobbles, and boulders typically up to about 2 to 3 feet in size in a silty sand matrix and overlies siltstone/claystone bedrock. Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge subdivision. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of loçalized subsidence. A sinkhole occurred in the parking lot adjoining the golf cart storage tent in January, 2005 located about %nlle to the south of Lot 39 which was backfilled and compaction grouted. To our knowledge, that sinkhole has not shown signs of reactivation such as ground subsidence since the remediation. Sinkholes possibly related to the Evaporite were not observed in the immediate area of the subject lot. Based on our present knowledge of the subsurface conditions at the site, it cannot be said for certain that sinkholes related to the underlying Evaporite will not develop. The risk of future ground subsidence on Lot 39 throughout the service life of the proposed building, in our opinion, is low; however, the owner should be made aware ,¡f the potential f,¡r sinkh,¡le devel,rpment. If further investigation of possible cavities in the bedrock below the site is desired, we should be contacted. FIELD EXPLORATION Tlre field exploration for the pro.iect was conducted on June 14, 2021. Two exploratory borings were drillecl at the locations shown on Figure 1 to evaluate the snbsurface conclitions. The borings were advanced with 4-inch diameter continuous flight augers powered by a truck- mounted CME-458 drill rig. The horings were logged hy a representative of Kumar & Associates, Inc. Kumar & Associates, lnc. o Project No. 21-7-435 -3- 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-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 subsoils consist of about l,Yzto 8 feet of relatively dense, mixed clay, silt, sand and gravel fill overlying nllto3vz feet of stiff, sandy silt and clay soils. Dense, slightly silty sandy gravel with cobbles was encountered below the silt and clay soils at depths of 5 to 8 feet down to the maximum explored depth of I5Yz feet. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in Boring 2. 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 relatively undisturbed drive samples, 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 llz-inch fraction) of the coarse granular subsoils are shown on Figure 5. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS Spread footing foundations placed on the relatively dense fill soil above the natural silty clay soils or on the natural silty clay soils should be adequate for support of the proposed residence with relatively low settlement potential. Footings bearing entirely on the dense gravel soils should have a low settlement risk. The bearing condition of the soils exposed in the excavation should be fuither evaluated at the time of construction. Kumar & Associates, lnc. @ Project No.21-7-435 -4- DßSIGN RE COMMDNDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the building be fbunded with spread footings bearing on the relatively dense fill soils or the natural silty clay soils if encountered. The clesign ancl constntction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the relatively dense fill soils or the underlying stiff silty clay soils should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. Post-construction settlement could be around 1 inch mainly if the bearing soils are wetted. 2) 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 unhcatcd arcas should bc 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 a lateral carth prcssurc corrcsponding to an cquivalcnt fluid unit weight of at least 55 pcf. 5) Any topsoil and loose disturbed soils should be removed and the footing bearing level extended down to the relatively dense fill soils or to the stiff silty clay soil beneath the fill. The exposed soils in footing area should then be moistened and compactecl. Additional stnrctural fill can consist of the onsite soils compacted to at least 98% of standard Proctor density at near optimum moisture content. New structural fill should extend laterally beyond the footing edges a distance equal to at least one-half the fill depth below the footing. 6) A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. Kumar & Associates, lnc. @ Project No. 21.7.435 5- FLOOR SLABS The 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 relatively well graded sand and gravel, such as road base, should be placed beneath garage level slabs for support. This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than I2o/o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95Yo 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 rock. UNDERDRAIN SYSTEM The proposed shallow (less than 4 feet) crawlspace and slab-on-grade garage should not require a perimeter underdrain system provided that the site grading recommendations contained in this report are followed. We recommend that below-grade construction, such as retaining walls, deep crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. If installed, 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 f,rnish grade and sloped at a minimum IYo to a suitable gravity outlet or drywell based in the gravel soils. Free- draining granular material used in the underdrain system should contain less than 2Yo passingthe 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 I% feet deep. An impervious membrane such as 30 mil 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. Kumar & Associates, lnc. o Project No. 21-7-435 -6- SURFACE DRAINAGE Proper surface grading and drainage will be critical to prevent wetting of the bearing soils and satisfactory perfonnance of the foundation. 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 95Yo 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 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inchcs in the first 10 feet in paved areas. Free-draining wall backfill (if any) should be 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 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 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 in the future. If the client is concernecl 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 pertbrmed. lf 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. Kumar & Associates, lnc. @ Project No.21-7-435 -7 - 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 recofitmendations, and to veriff that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recoûìmendations 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 & Associateso James H. Parsons, P Reviewed by:ffi*/. Steven L. Pawlak, P.E. JHPlkac tt 58660 7/ltl/zt Kumar & Associates, lnc.(i Project No. 21-7-435 I LOT 40 98 .0 Y 126 .9 | LOT RTY LINE SETBACK 1 oe/rt / 1 0 50 APPROXIMATE SCALE-FEET 78.0 LOT 39 12 .0 SETBACK O 2 PROPERTY T TNE s BORING 1 12,6.e1a 21 -7 -435 Kumar & Associates LOCATION OF TXPLORATORY BORINGS 1Fig ¡ ts BORING EL. 1 03 1 BORING 2 EL. 101.5' 0 0 23/ 12 WC=5.5 DD= 1 00 -200=69 17 /12 WC=6.3 DD= 1 08 50/2.5521/12 WC=6.7 DD= 1 06 q F- L¡J LJtL I-F o_ t¡Jô 17 /6,32/6 71 /12 F L¡J t¡JtL I-t-fLLIo 10 1053/6 36/6, s0/5 15 '15 50/2.5 20 20 WC= 1 .0 +4=65 -200='l 0 21 -7 -435 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 ¡ LEGEND ñ FILL: SLIGHTLY GRAVELLY SANDY SILTY CLAY, VERY STIFF, SLIGHTLY MOIST, TAN TO LIGHT BROWN. CLAY AND SILT (CL-ML): SANDY, VERY STIFF, SLIGHTLY MOIST, LIGHT BROWN TO TAN GRAVEL (CU): SINOY, SLtcHTLy StLTy W|TH COBBLES, PROBABLE BOULDERS, DENSE, SLIGHTLY MOIST, LIGHT BROWN, ROUNDED ROCK. DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE i DRIVE SAMPLE, 1 3/8-|NCH t.D. SpLrT SPOON STANDARD pENETRATTON TEST. cz/tc DRIVE SAMPLE BLOW COUNT. INDICATES THAT 23 BLOWS OF A 14O-POUND HAMMER2¿t tz FALLTNG J0 TNcHES wERE REQUIRED To DRtvE THE sAMpLER t2 tNcHES. I enacrrcAL AUGER REFUSAL. NOTES 1 , THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 1 4, 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 OBTAINED BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED AND THE ASSUMED CONTOUR ELEVATION. 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); DD = DRY DENSITY (PCt) (ISTM D2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913); -2oo= PERCENTAGE PASSING N0. 200 SIEVE (ASTM D1140). 21 -7 -435 Kumar & Associates LEGEND AND NOTES Fig. 5 I E I I SAMPLE 0F: Slightly Grovelly Sondy Silty Cloy (Fill) FROM:Boringl@5' WC = 6.7 %, DD = 106 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING àe JJ L¡J =I,t'' I z_otr o =o U1zo() 1 0 -1 -2 -3 -4 1.0 APPLIED PRESSURE _ KSF 10 r00 àe JJ UJ =t/1 I z.otr o =otr)z.oo 1 0 -1 -2 -5 APPLIED PRESSURE - KSF SAMPLE OF: Sondy Cloy ond Silt FROM:Boring2@2.5' WC = 6.5 %, DD = 108 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 21 -7 -435 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 4 t E9 9r r& ?,Á =et ñ 100 90 ao 70 60 50 ,t0 50 20 10 o fo 20 30 40 50 60 70 ao 90 t00 I 6 ÐIAMETER OF IN MI RS CLAY TO SILT COBBLES GRAVEL 65 % SAND 25 LIQUID LIMIT SAMPLE OF: Slighlty Silty Scndy Grovel % PLASTICITY INDEX SILT AND CLAY 10 % FROM: Boring 2 gt 7.5' & 10' COMBINED Th6s6 t€sl rosulls opply only lo lhe somples whlch woro loslod. fhellsllng reporl shqll nol bs reproducod, €xcapl ln full, wllhoul lh€ wrlll€n opprovol of Kumor & AssocÌol€s, lnc. Slovo onolysls l€sllng ls p€rformod ln occordonca wlth ASTM D69,l5, ASTM D7928, ASÍM Cl36 ond/or ASIM 011,10. HYDROMETER ANALYSIS SIEVE ANALYSIS TIME REÂDINCS 24 HRS 7 HRS CLEAR SQUARE OPENINGS t/an I tltr I f_t+ l U.S. STANDARD SERIES I i I l L I I I I I I I I SAND GRAVEL FINE MEDTUM ICOARSE FINE COARSE 21 -7 -435 Kumar & Associates GRADATION TEST RTSULTS Fis. 5 I (+rt iiË*å'ffifffifn'iiÍ å' *"TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.21-7-435Sandy Clay and SiltSlightly Silty Sandy GravelSlightly Gravelly SandySiltv Clav Gill)0125651061086.3016.7Slightly Gravelly SandySOIL TYPE1005.52t/,691ATÏERBERG LIMITSGRADATIONSAMPLE LOCATIONDEPTHBORINGLIQUID LIMlTUNCONFINEDCOMPRESSIVESÏRENGTHPERCENTPASSING NO.200 sIEVENATURALDRYDENSITYNATURALMOISTURECONTENTSANDt:/,)GRAVEL(%)PLASTICINDEX52%1% &, r0combined2