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HomeMy WebLinkAboutSubsoil Study for Foundation Design 02.11.2022l(+A#ffii,ffi:iri'"* r,n anssrycr oqmcd compsry 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 Sumrnit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE AI\D BARN 9174 HIGHWAY 82 GARFTELD COUNTY, COLORADO PROJECT NO.22-7-115 FEBRUARY 11,2022 PREPARED FOR: BRANDON COWHEY 571 RIVERBEND WAY GLENWOOD SPRINGS, COLORADO 81601 cow hev bra n don @,q mail.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS SUBSIDENCE POTENTIAL. FIELD EXPLORATION SUBSURFACE 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 . GRADATION TEST RESULTS TABLE 1 - SUMMARY OF LABOMTORY TEST RESULTS a-J- J 3- _/,_ -3- -4- -5- -{- _A_ _A_ _1- -7 - Kumar & Associates, lnc. @ Project No. 22-7-'ll5 -J- PURPOSE AND SCOPE OF STUDY T'his report presents the results of a subsoil study for a proposed residence and bam to be located at9l74 Highway 82, 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 Brandon Cowhey, dated January 13,2022. A flreld 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 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 At the time of our study, design plans for the residence had not been developed. For the purposes of our analysis, we assume proposed residence will be a wood-framed structure with attached garugeand a detached barn. 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 4 to 7 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 gentle slope down to the southwest. The lot is situated on a terrace above the Roaring Fork River, which borders the lot on the southwest. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies most of the lower Roaring Fork Valley, including the subject site. These rocks are a sequence of gypsiferious shale, fine- Kumar & Associates, lnc. o Project No. 22-7-'115 4 grained sandstone/siltstone and limestone with some massive beds of gypsum. There is a possibilify 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, howevero 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 at the 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. FIELD EXPLORATION The field exploration for the project was conducted on January 18,2022. Three 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 and Associates. Samples of the subsoils were taken with a l%inchand2inch 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, below about 6 inches of topsoil, consist of about l%to 3% feet of stifl sandy silt underlain by relatively dense, silty sandy gravel with cobbles and probable small boulders Kumar & Associates, lnc. o Project No. 22-7-1'15 -5- (alluvium) down to the maximum depth explored of 8 feet. Drilling in the dense granular soils vrith 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 a small diameter drive sample (minus l%-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 buildings 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. l) Footings placed on the undisturbed natural granular soils below all sandy silt 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 I inch or less. 2) The footings should have a minimum width of 16 inches for continuous walls and .2 feefforisolated Pads. -----3) Exterior footings and footings beneath unheated areas should be provided with dequate soil cover above their bearing elevation for frost protection. Placement of foundations at least 36 inches below exterior grade is typically used in this atea. 4) 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 corresponding to an equivalent fluid unit weight of at least 45 pcf for the onsite sand and gravel soil as backfill. Kumar & Associates, lnc. @ Project No. 22-7-115 -6- 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. 6) A representative ofthe geotechnical engineer should observe excavations prior to concrete placement to evaluate bearing conditions. FLOOR SLABS The natural on-site granular soils, exclusive of topsoil, are suitable to support lightly loaded slab- on-grade construction. The sand and silt soils have settlement potential which could result in some slab movement if the bearing soils become wetted. To reduce the effects of some differential movement, floor slabs in the garage and barn areas 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 interion slabs-on-grade for subgrade support. This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than l2%o passing the No. 200 sieve. If slab-on-grade construction is used inside the house, some sub-excavation of the silt soils may be needed to reduce potential settlement. 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 granular soils or suitable imported granular fill devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM 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 constructiono such as retaining walls, crawlspace and basement areas, be protected from weffing 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 I foot below lowest adjacent finish grade and sloped at a minimum lYoto s) Kumar & Associates, lnc. o Project No. 22-7-115 -7 - a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain system should contain less than 2Topassingthe 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 lYzfeet 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 should be 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 l0 feet in unpaved areas and a minimum slope of 3 inches in the first 10 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 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 atthis 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 I, 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. Kumar & Associates, lnc. @ Project No. 22-7-'115 -8- 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 verify 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 fill by a representative of the geotechnical engineer. Respectfully Submitted, . K$sxlar & .4ss*c*st*s, Xme- David A. Noteboom, StaffEngineer Reviewed by: Daniel E. Hardin, DEHlkac Kumar & Atscclateso lne. tr Proiec{ t{a. 32-?-tl$ s T $ * NOT TO SCALE Fig. 1Kumar & Associates LOCATION OF EXPLORATORY BORINGS22-7-115 * f BORING 1 BORING 2 BORING 5 0 0 13/ 12 WC=6.1 DD=90 -2OO=52 1e /6 WC=3.8 F UJlrjl! IIF TL UJo DD=90 -2OO=47 FlrlUL! I-F[Lulo 5 5 5s/12 WC= 1 .5 +4=55 -2OQ=12 50/6 so/5 10 10 LEGEND N TOPSOIL; SANDY CLAY AND SILT, ORGANICS AND ROOTS, FIRM' MOIST' BROWN SILT (ML); VERY SANDY, STIFF, SLIGHTLY MolST, BROWN' SLIGHTLY POROUS W GRAVEL (GM); SANDY, SILTY, WITH COBBLES AN VERY DENSE, SLIGHTLY MOIST, BROWN, ROUNDE DS DR MALL BOULDERS, DENSE TO OCKS. DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE. I DRTVE SAMPLE, 1 3/8-INCH l.D. SPLIT SPOoN STANDARD PENETRATION TEST. AI'^ DRIVE SAMPLE BLOW COUNT' INDICATES THAT 13 BLOWS OF A 140-POUND HAMMER ''/ '' FALLTNG 30 tNcHES WERE REeU|RED To DRIVE THE SAMPLER 12 lNcHES. I nnlcrrcnL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 18, 2021 WITH A 4-INCH-DIAMETER CONTINUOUS-FLIGHT POWER AUGER. 2. THE EXPLORATORY BORINGS WEBE LOCATED BY THE CLIENT. 3. 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 CoNTENT (%) (ASTM D2216); DD = DRY DENSITY (PCT) (ISTV D2216)I +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6915); _2QO= PERCENTAGE PASSING NO.2OO SIEVE (ASTM Dl140). 22-7 -1 15 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 e ? h E & H 100 90 ao 70 80 50 & 30 20 to o o to 20 JO & 50 60 70 ao eo 42 2s too DIAMETER OF IN CLAY TO SILT COBBLES GRAVEL 55 % SAND LIQUID TIMIT SAMPLE OF: Sllty Sondy Grov6l 53% PLASTICITY INDEX SILT AND CLAY 12 % FROM:BorlnglO5' Thcr. l.tl rolull3 qpply only lo lh. rqmpl.s vhlch v.r. lcllad. Thr lcsllng ruporl sholl nol b. rcproduccd, cxc.pl ln full. wlihoul lh. wrltlrn qpprcvql of Kumqr & Assoclotcs, lnc, Sl.vc onolytl! lasllng ls p.rtom.d ln occordonci wllh ASTM D69t5, ASTM D7926, ASTM C156 ond,/or ASTM D11,10, SIEVE ANALYSISHYDROMETER ANALYSIS f,YE RilDING 24 HS 7 HRS U.S. STAXD RD SERIES al rt CLEAR SQUARE OPEIIINOS tti' t/a. 7 t/r- I t .......... L..............;... t:J::l tl .........r...1... '1 .-.....t-...--r --------i---r--'-*t-*.-"- -:-t-- f...-:.. I ...............t.....i.--: I -- "-:-t-- I '-----l-----i''- 1J r1,.. --.----|-.*.1**- .......................i...........i........... . . . . . . . . . . . . . .1 . . . . . t . ---i-l- ;fi:....i'. -'--------?------ i--------zli---,1 -----l----i------r-i--z|....- -----i---i- -.. ..i .. ..1... '__ .. _.'_- l---t'.-- tl r " i rl r SAND GRAVEL FINE COARSEFINEMEDTUM ICOARSE 22-7 -1 15 Kumar & Associates GRADATION TEST RESULTS Fig. 3 lffi t. Xmrar & Associatc, he.* Geotechnical and Materials Engineen and Fnyironrnental Scientists TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Silty Sandy Gravel Sand and Silt SOIL TYPE Sand and Silt (osfl UNCONFINED COMPRESSIVE STRENGTH lolol PLASTIC INDEX ATTERBERG LIMITS lolol LIQUID LIMI'T ,52 2I 47 PERCENT PASSING NO. 200 stEvE SAND l'tt 33 (%) GRAVEL 55 6.1 90 90 NATURAL DRY DENSITY (ocfl{%l NATURAL MOISTURE CONTENT 1.3 3.8 (ftt DEPTH 2% 5 2Y) I aJ SAMPLE LOCATION' BORING No.22-7-115