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HomeMy WebLinkAboutSubsoil Studyt(+rtiiffifimfmF."" An Employcc Owncd Compony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumaru$a,com www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Spríngs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR TOUNN¡TION DESIGN ÈnoposnD RESTDENCElor r,'coRYELL RANCH STONEF'LY NNTVN GARFIELD COUNTY, COLORADO PROJECT NO.2l-7-492 JULY 19,2021 PREPARED FOR: PEAK 3 STONEFLY LLC C/O PEAK 3 CONSTRUCTION + DEVELOPMENT ATTN: BRYANT RAGAN 601 EAST HOPKINS AVENUE, SUITE 202 ASPEN, COLOR.A.DO 81611 brvant@.oeak3 asnen.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS SIIBSIDENCE POTENTIAL. FIELD EXPLORATION SUBSURFACE CONDITIONS DESIGN RECOMMENDATIONS .. FOLTNDATIONS FLOOR SLABS UNDERDRAIN SYSTEM.... SURFACE DRAINAGE. LIMITATIONS FIGURE 1 . LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - GRADATION TEST RESULTS TABLE 1 _ SUMMARY OF LABORATORY TEST RESULTS -J- a-J- -3- -4- -4- -5- -7 - Kumar & Associates, lnc. @ Project No.2l-7-492 -J- PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 1, Coryell Ranch, Stonefly Drive, Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recoÍìmendations for the foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to Peak 3 Stonefly, LLC dated }lday 26,2021. 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 andlaboratory 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 The proposed residence will consist of a single-story wood-framed structure with attached garage and a detached barn and ADU. Ground floors will be structural floor over crawlspace in the residence and slabs-on-grade for the garage and barn. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 6 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 lot was vacant of structures at the time of our visit. Vegetation consists of grass and weeds, and the ground surface is relatively flat with a slight slope down to the east and southeast. Elevation difference across the buildin g area is about 2 feet. The lot is bordered on the northeast by the Roaring Fork River, and on the south by Stonefly Drive. Kumar & Associates, lnc. o Project No.21-7-492 -4- SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the lower Coryell Ranch Subdivision. These rocks af,e a sequence of gypsiferious shale, fine-grained sandstone/siltstone and limestone with some massive beds of gypsum. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the property. 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 broad subsidence areas and sinkholes have been observed. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork River valley. No evidence of subsidence or sinkholes were observed on the property or 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 can not be said for certain that sinkholes will not develop. The risk of future ground subsidence atthe site throughout the service life of the structure, in our opinion is low, however the owner should be 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 lune 21,2021. Three exploratory borings were drilled at the locations shown on Figure I 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 and Associates. Samples of the subsoils were taken with a l3/a 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 aî indication of the relative density or consistency of the subsoils. Depths at which the samples v/ere 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. ô Project No.21-7-492 -5- SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. In Borings 1 and 3, the subsoils below about 6 inches of topsoil consist of slightly silty to silty sandy gravel with cobbles and probable small boulders down to the maximum depth explored, 8 feet. In Boring 2, the subsoils below about 6 inches of topsoil consist of slightly siþ to silty sandy gravel with cobbles and probable small boulders with interbedded layers of silty sand down to the maximum depth drilled of 9 feet. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in all three borings in the deposit. 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 lVz-inch fraction) of the coarse granular subsoils are shown on Figure 3. 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. 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. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) 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 1 inch or less. 2) The footings should have a minimum width of 16 inches for continuous walls and 2 feet for isolated pads. Kumar & Associates, lnc. @ Project No.21-7-492 -6- 3)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 10 feet. Foundation walls acting as retaining structures should also be designed to resist a lateral earth pressure coffesponding to an equivalent fluid unit weight of at least 45 pcf for the onsite sand and gravel soil as backfill. All topsoil 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. 4) FLOOR SLABS The natural on-site granular 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 well graded sand and gravel (such as road base) should be placed beneath 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 12o/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 fill can consist of the on- site granular soils devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM 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 øeate a perched 5) 6) Kumar & Associates, lnc, o Project No.21-7-492 -7 - 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 and wall drain 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 1o/oto a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain system should contain less than 2%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 I%feet deep. SIIRFACE DRAINAGE 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 95o/o of the maximum standard Proctor density in pavement and slab areas and to at least 90/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 backfrll 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. o Project No. 21-7-492 -8- 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 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 veriff that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recoÍlmendations 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, I(umar & Associates, Inc. David A. Noteboom, Staff Engineer Reviewed by: Steven L. Pawlak, P. SLPlkac I Kumar & Associates, lnc, @ Project No.21-7-492 Ê I LOT 1 BORING 1o BORING a"--, ,"e .*.ñTO STONEFLY DRIVE € .s Fg'tr ""e I ooóN LOT 2 ".-Ç$(ñs ."-Ñ 25 0 APPROXIMATE SCALE_FEEÏ 21 -7 - 492 Kumar & Associates LOCATION OF TXPLORATORY BORINGS Fig. 1 Ë ,ö I WC= 1 .7 +4=47 -2Q0=1 4 BORING 1 EL. 6082' BORING 2 EL. 6082.5' BORING 3 EL. 6081.5' 0 0 l-LI t¡J LL I-F-o- L¡Jâ 82/ 12 62/12 50/3 F UJ t¡JtL I-Fo- Ldô 5 Â 63/12 ss/12 50/5 so/2.5 s8/6 10 '10 NhvN TOPSOIL; SANDY TO VERY SANDY CLAY, SOME GRAVEL, ROOTS AND ORGANICS, FIRM' SLIGHTLY MOIST, LIGHT BROWN. GRAVEL AND SAND (GM-SM); COBBLES PROBABLE SMALL BOULDERS, SLIGHTLY SILTY TO SILTY, VERY DENSE, SLIGHTLY MOIST, LIGHT GRAY TO GRAY AND TAN. ROUNDED ROCK GRAVEL AND SAND (GP-SM); COBBLES PROBABLE SMALL BOULDERS, SLIGHTLY SILTY TO SILTY, WITH LAYERS OF SILTY SAND, VERY DENSE, SLIGHTLY MOIST, REDDISH TAN TO TAN. ROUNDED ROCK. i DRTVE SAMPLE, 1 3/8-|NCH l.D. SPLIT SPOON STANDARD PENETRATION TEST 82/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 82 BLOWS OF A 14o_POUND HAMMER FALLING 50 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. I PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 21 , 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 ACCURAÏE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT ÏHE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT ÏHE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ISTU OOSIS); _2OQ= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140). WC=1.1 +4=39 -200=8 21 -7 -492 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 ë 4 .E ¿; ! SIEVE ANALYSISHYDROMETER ANALYSIS U.S. STANDARO SERIES CLEAR SQUARE OPENINGS ttÀ. ?Ja6 1 t/a6 / TIME READI{6S i / / I _-.i.- I / I ¡ 6 f 100 90 80 70 60 50 10 30 20 t0 o o t0 20 30 40 50 60 70 a0 90 toorir I .o37 .o75 DIAMETER OF PA INM CLAY TO SILT COBBLES GRAVEL 47 % SAND LIQUID LIMIT SAMPLE OF: Silty Sond ond Grovel 39% PLASTICITY INDEX SILT AND CLAY 14 % FROM: Borlng 1 O 2.5' & 5' (Gombined) à to0 90 a0 70 60 50 ,to 30 20 10 0 0 10 20 30 40 50 60 70 80 g0 100 É .075 .300 .600 I .l ,425R OF PARTICLES IN MI 152 RS CLAY TO SILÏ COBBLES GRAVEL 39 % SAND 53 LIQUID LIMIT SAMPLE OF: Slightly Silty Sond ond Grovel % PLASTICITY INDEX SILT AND CLAY 8% Thcse l6sl rêsulls opply only to lh€ somples whlch wrrc t€st€d, th. icallng report sholl nol bo roproducsd, óxcepl in full, wllhoul lh6 written opprovol of Kumqr & Assoc¡otss, lnc, Slôvê dnolysls lostlng ls pcrformcd ln occordonco wlth ASÍM 06913, ASIM 07928, ASTM C136 ond/or ASTTJ Dl1,{0. FROM: Boring 2 O 5' & 7.5' (Combined) SAND GRAVEL FINE COARSEFINEMEDIUMCOARSE SIEVE ANALYSISHYDROMETER ANALYSIS CLEAR SOUARE OPEflINGS / fIME REAOINOS sÊRtEs / I I I I I I l i' GRAVELSAND COARSEFINEMEDTUM ICOARSE FIN E 21-7 -492 Kumar & Associates GRADATION TEST RESULTS Fig. 3 l(+rtH,Ë*fi'ffiffint':iü'*"TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.2l-7-492SAMPLENATURALMOISTURECONTENTNATURALDRYDENSITYUNCONFINEDCOMPRESSIVESTRENGTHGRAVELSANDPERCENTPASSING NO.200 stEvEPLASTICINDEXPITDEPTHLIQUID LIMITSOIL TYPE(/"1(%)12/z and 5combined1.14739T4Silty Sand and Gravel25 andT%combined1.139538Slightly Siþ Sand andGravel