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Home My WebLink AboutSubsoil Study for Foundation Design 04.15.2021I .*rt iiffilf;',i#f'$ffn'"'Ê; ;'' ** An Employcc Owncd Compony 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 580 TRONBRTDGE BLUE HERON DRIVE GARFIELD COUNTY, COLORADO PROJECT NO.21-7-276 APRrL 15,2021 PREPARED FOR: scIB, LLC ATTN: LUKE GOSDA 0115 BOOMERANG ROAD' SUrTE 52018 ASPEN, COLORADO 81611 luke.gosda@sunriseco.com 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 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS -1 -1 1 a- -z-- .t 3- .-3- -3 - -3 - 4 5 5 6 Kumar & Associates, Inc. @ Project No.21-7-276 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 58, 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 March 16,202I. A f,reld 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 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 Development plans for the lot were preliminary at the time of our study. In general, the proposed residence will be a one- and two-story wood-frame structure with attached garage. Ground floors will be a combination of structural over crawlspace and slab-on-grade. Grading for the structure is assumed to be relatively minor with cut depths between about 2 to 4 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 at the time of our field exploration. The ground surface is gently sloping down to the north in the building area. A steep cut slope from previous subdivision development is located south of the building area sloping down to the north at a grade of around 40 percent. Vegetation consists of grass and weeds. Kumar & Associates, lnc. @ Project No.21-7-276 SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge development. 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 the Ironbridge development. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork 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 58 throughout the service life of the proposed residence, in our opinion, is low and similar to other lots in the area of similar subsurface profiles; 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 March 22,202I. 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 were logged by a representative of Kumar & Associates, Inc. Samples of the subsoils were taken with l% inch and 2 inch LD. 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 retumed to our laboratory for review by the project engineer and testing. Kumar & Associates, lnc, @ Project No.21-7-276 -3- SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about 1 foot of topsoil overlying medium stiff to very stiff, sandy clay and silt down to between 6Yz and 8% feet deep where medium dense to dense, silty sandy gravel with cobbles was encountered to the maximum explored depth of 17% feet. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit. Laboratory testing performed on samples obtained from the borings included natural moisture content and density, finer than sand grain size gradation analyses and unconfined compressive strength. Results of swell-consolidation testing performed on relatively undisturbed drive samples, presented on Figures 4 and 5, indicate low to moderate compressibility under existing low moisture conditions and light loading and a varied low collapse to low swell potential when wetted under constant light surcharge. 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 moist to slightly moist. FOUNDATION BEARING CONDITIONS The upper clay and silt soils encountered in the borings possess low bearing capacity and a low to moderate settlement potential if wetted. Shallow spread footings placed on the clay and silt soils can be used lor support of the proposed residence with a risk of foundation settlement if the bearing soils become wetted. Proper surface drainage as described in this report will be critical to the long term performance of the structure. DESIGN RECOMMENDATIONS FOI.INDATIONS 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. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural soils should be designed for an allowable bearing pressure "{|]9þ! Based on experience, we expect Kumar & Associates, lnc. @ Project No.21-7-276 -4- 2) settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. Additional post-construction settlement of around I inch could occur if the bearing soils become wetted. The footings should have a minimum width of 18 inches for continuous walls and 2 feef 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 helow exterior grade is typically used in this area. Continuous foundation walls should be heavily 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 earth pressure corresponding to an equivalent fluid unit weight of at least 55 pcf for the on-site soils as backfill. Topsoil and any loose disturbed soils should be removed and the footing bearing level extended down to the relatively firm natural 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) 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 relatively well graded sand and gravel such as road base should be placed beneath interior 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 2o/o passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95o/o of maximum standard Proctor density at a moisture content near optimum. Required hll can consist of the on- site soils devoid of vegetation, topsoil and oversized rock or a suitable imported material such as road base. Kumar & Associates, lnc, o Project No.21-7-276 5 LINDERDRAIN SYSTEM It is our understanding the ground finished floor elevation of the residence is at or above the surrounding grade. Therefore, a foundation drain system is not recommended. It has been our experience in the arcathat 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 basement areas, if provided, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain system. An underdrain is not recommended around the crawlspace area to help limit the potential for wetting below the shallow footings. If the finished floor elevation of the proposed structure has a floor level below the surrounding grade, we should be contacted to provide recommendations for an underdrain system. All earth retaining structures should be properly drained. SURFACE DRAINAGE It will be critical to the building performance to keep the bearing soils dry. The following drainage precautions should be observed during construction and maintained at all times aÍter 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 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 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. Graded swales should have a minimum slope of 3% 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 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. Kumar & Associates, lnc. @ Project No.21-7-276 -6- LIMITATIONS This study has been conducted in accordance with generally accepted 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 concerned about MOBC, then a professional in this special field of practice should be consúted. 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 thatre-evaluation of the recommendations may be made. This report has been prepared 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 modifications to the recommendations presented herein. 'We recommend on-site observation of excavations and foundation bearing strata and testing of structural frll by a representative of the geotechnical engineer. Respectfully Submitted, Kurnar & Associates, IRc. Wfr.pea¡+n*/ James H. Parsons, P.E. Reviewed by: Steven L. JHPlkac Kumar & Associates, lnc. 6'Project No.21.7-216 I e E 97 ô¡- drïf" Ø.ð 100.0' 80 ò! rRornnrv L]NE LOT 51 102.0'1,,I PROPERTY LINE 9 SETBACK 9B L21 .1', \ r25.3 15 0 0 APPROXIMATE SCALE-FEET Bs. s 1f I Ô t 12 .8' 12. a'\BORING 1 o PROPERTY LINE /,6.0' BORING 2 o SE:I'BACK qq \ | LOT 58 21 -7 -276 Kumar & Associates LOCATION OF EXPLORATORY BORINGS 1Fig. I BORING 1 EL. 1 00' BORING 2 EL. 100.5' 0 6/ 12 WC= 1 5.8 DD= 1 07 -2OO=84 UC=2,65017 /12 WC=6.4 DD= 1 00 EJ 22/12 WC=4.6 DD=101 -200=86 21/12 WC=8.1 DD=93 Ã 50/6 2e/12 t--- t¡J t¡JtL I-F o_ t¡Jô 10 10 F- L¡l L¡J LL ITFo-t¡lô 66/12 15/ 12 15 1546/12 20 20 21 -7 -276 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 I ¡ E ñ I LEGEND N TOPSOIL: CLAY, SILTY, SANDY, SCATTERED GRAVEL, ORGANICS, ROOT ZONE, FIRM, MOIST, BROWN. CLAY AND SILT (CL-ML): SANDY, MEDIUM STIFF TO VERY STIFF, MOIST To SLIGHTLY MOIST, BROWN. GRAVEL (GM): SANDY, SLIGHTLY SILTY AND SItTY, COBBLES, POSSIBLE BOULDERS MEDIUM DENSE TO DENSE, SLIGHTLY MOIST, BROWN AND GREY. DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE ¡ DR|VE SAMPLE, 1 5/8-INCH l.D. SPLIT SPOON STANDARD PENETRATIoN TEST A- IAı DRIVE SAMPLE BLOW COUNT. INDICATES THAT 17 BLOWS OF A 14o-POUND HAMMER "/ '' FAI:LTNG 30 TNcHES wERE REeUIRED To DRtvE THE sAMpLER 12 tNcHES. I PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 22, 2021 WITH A 4-INCH DIAMETER CONTINUOUS_FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY TAPING 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 TOCATIONS 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 RESULÏS: WC = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (PCt) (ASTV D2216); _ZQQ= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1140); Uc = UNCONFINED COMPRESSIVE STRENGTH (psf) (ASTM D 2166) 21 -7 -27 6 Kumar & Associates LEGEND AND NOTES Fig.3 ¡ Ê I SAMPLE OF: Sondy Silty Cloy FROM:Boringl@2.5' WC = 6.4 %, DD = 100 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING in 1 àq JJ t¡J =U) I z.otr ô =o U''z.o(J 0 -1 -2 -3 APPLIED PRESSURE - KSF 10 100 21 -7 -276 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 4 I E 9 I SAMPLE OF: Sondy Silt ond Cloy FROM:Boring2e^4' WC = 8.1 %, DD = 95 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 3holl not full, without ConBolidot¡on 1 0 ñ JJ t¡J =Ul I z.otr ô =o U)z.o(J -1 -2 -3 -4 -5 -6 -7 -8 APPLIED PRESSURE - KSF 10 100 21 -7 -276 Kumar & Associates SWELL-CONSOLIDATION TTST RESULTS Fig. 5 lGrtiiry*['.ffiftrin'::ii;*'"TABLE 1SUMMARY OF LABORATORY TEST RESULTSSandy Silt and Clay938.14Sandy Silty ClaySOIL TYPE2,650r0715.884II22y,5ATTERBERG LIMITSSandy Silty ClaySandy Silt and ClayGRADATION1001016.44.6SAMPLE LOCATIONDEPTHBORINGLIQUID LIMITUNCONFINEDCOMPRESSIVESTRENGTHPERCENTPASSING NO.200 stEvENATURALDRYDENSITYNATURALMOISTURECONTENTSAND(f/"1GRAVEL(%)PLASTICINDEXNo.2'l-7-276