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HomeMy WebLinkAboutSubsoil Studyrcrf iiffififfiiffin*;-"'5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com wwwkumatusa,comAn Employcc otrncd Co'mPonY Office Locations: Denver (FlQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado May 4,2022 RECEIVED Eddie Mumay P. O. Box 551 New Castle, Colorado 81647 eddie (ã.oaci fi csh eetm eta I . net it¡hi 1 3 2tì?? GARFIELD COUNTY COMMUNITY DEVELOPMENT Project No. 22-7 -227 Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 13, The Rapids, Rapids View Lane, Garfield County, Colorado Dear Eddie: As requested, Kumar & Associates performed a subsoil study for design of foundations at the subject site. The data obtained and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. The study was conducted in accordance with our agreement for geotechnical engineering services to you dated March 14, 2022. Proposed Construction: The residence will be a two story wood frame structure located on the lot as shown on Figure 1. Ground floors will be structural over crawlspace in the living area and slab-on-grade in the garcge area. Cut depths are expected to range between about 3 to 5Yz feet' Foundation loadings for this type of construction are assumed to be relatively light and typical of the proposed type of construction. If building conditions or foundation loadings are significantly different from those described above, we should be notifîed to re-evaluate the recommendations presented in this report. Site Conditions: The lot was vacant and the ground surface appeared mostly natural at the time of our field exploration. The teruain is relatively flat with a strong slope down to the north towards the Colorado River which borders the north side of the lot. There is a moderately steep slope down about 6 to 8 feet to the river in the northern part of the lot. The river was a low flow at this time. Vegetation consists of grass and weeds. The adjacent lots are vacant. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered, below about I to l% feet of topsoil, consisted of loose, very silty sand down to depths of from about 2%to 5Yzfeetunderlain by relatively dense, slightly silty sandy gravel and cobbles (coarse granular soils) down to the pit depths of 6 and 7 feet. Results of swell-consolidation testing performed on a relatively undisturbed sample of the very silty sand -2- soils, presented on Figure 3, indicate moderate to high compressibility under conditions of Ioading and a wetting with a moderate hydro-compression potential. Results of a gradation analysis performed on a disturbed bulk sample of underlying coarse granular soils (minus 5-inch fraction) obtained from site are presented on Figure 4. No groundwater was observed in the pits at the time of excavation and the subsoils were moist to slightly moist. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recommend spread footings placed on entirely the undisturbed natural coarse granular soils designed for an allowable bearing pressure of 2,500 psf for support of the proposed residence. The very silty sand soils are compressible and should be removed below the footing areas to bear the footings entirely on the underlying dense coarse granular soils and provide a relatively low risk of settlement. This will likely require subexcavation below design bearing elevation in areas. It should be feasible to re- establish design footing bearing elevation with compacted structural fill consisting of imported single pass "pit-run" sand and gravel or ofaggregate base course' It is feasible to bear the footings on the upper very silty sand soils with some risk of settlement and distress. Footings placed on the very silty sand soils should be designed for an allowable bearing pressure of 1,000 psf. We should further evaluate the feasibility of bearing the footings on the very silty sand soils at the time of excavation if this is the design approach used' The footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. All topsoil and any loose disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural soils and the subgrade compacted. If the footings are designed to bear on the natural coarse granular soils, all very silty sand soils should also be removed. Structural fill below footings areas should be compacted to at least 98olo standard Proctor density at a moisture content near optimum. The structural fill should extend laterally beyond the edges of the footings a distance equal to at least %the depth of fill below the footings. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. placement of footings at least 36 inches below the exterior grade is typically used in this area. Continuous foundation walls should be well 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 based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as backfill. 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 Kumar & Assocíates, lnc, @ Project No. 22-7-227 -3- 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 gravel should be placed beneath slabs for support and to facilitate drainage. This material should consist of minus 2-inch aggregate with less than 50Yo passing the No. 4 sieve and less than 12% 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 topsoil and oversized (plus 6-inch) rocks, or of suitable imported granular soils. Underdrain System: It is our understanding the proposed finished floor elevation at the lowest level is at or above the surrounding grade. Therefore, a foundation drain system is not required' 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 runoffcan also create a perched condition. We recommend below-grade construction, such as retaining walls and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain system. If the finished floor elevation of the proposed structure is revised to have a floor level below the sugounding grade, we should be contacted to provide recommendations for an underdrain system. All earth retaining structures should be properly drained. 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 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 sunounding 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 fîrst l0 feet in pavement and walkway areas. 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 5 feet from the building' Kumar & Associates, lnc. @ Project No. 22-7-227 -4- Limitations: This study has been conducted in accordance with generally acce'pted geotechnical engineering princþles and practices in this area at this time. rtVe make no waranty either express or implied. The conclusions and recommendations submitted in this report are based upon the dat¿ obtained from the exploratory pits excavated aI the locations indicated on Figure 1 and to the depths shown on Figure 2,theproposed type of construction, and our experience in the area. Our services do not include determining the presence, prevention or possibility of mold or otherbiological 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 pits and variations in the subsurface conditions may not become evide,lrt until excavation is performed. If conditions encountered during construction appear different from those described in this report" we should be notified at once so 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 implemelrtation of our recommendations, and to veriry 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 sfrata and testing of structural fill by a representative of the geotechnical engineer. If you have any questions or if we may be of further assistance, please let us know. Respectfully Submitted, Kumar & David A. Young, P ts DAY/kac attachments Figure 1-Pits Figure 2 - Logs of Exploratory Pits Figure 3 - Swell-Çonsolidation Test Results Figure 4 - Gradation Test Results Table 1 - Summary of Laboratory Test Results Kumar & Associates, lnc. o Projec't No. 22-7-227 PIT I 2 I : I I I I I I T! :i {l $st/ è q I I I I I I I*__.._j I PIT 1 ù RAPIDS VI LANE LOT 13. THE RAPIDS 1 15 APPROXIMATE SCALE_FEET *-----ljàf,-------- - ---. 22-7 -227 Kumar & Associates LOCATION OF EXPLORATORY PITS 1Fig. PIT 1 Ptï 2 0 0 WC= 12.3 DD=85 -200=38 WC=6.5 DD=84l- TJt¡l LL I-t---È IJô 5 I *¿=83- -2oo=1 WC=3.7 DD=85 5 l- Ltl LJ LL I-t- o_ L!Õ t0 10 LEGEND TOPSOIL; VERY SILTY SAND, LOOSE, MOIST, DARK BROWN, ROOT ZONE. SAND (SM); VERY SILTY, LOOSE, MOIST, BROWN GRAVEL AND COBBLES BROWN, PRIMARILY ROU (GM-cP); SANDY, SLIGHTLY SILTY, DENSE, SLIGHTLY MOIST, MIXED NDED ROCKS. F t HAND DRIVE SAMPLE. DISTURBED BULK SAMPLE NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MARCH 16,2022 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THE EXPLORATORY PITS ARE PLOTTED TO DEPTH. 4. THE EXPLORATORY PIT LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT ÏHE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216): DD = DRY DENSITY (pcf) (ASTM D 2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422); -200= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1 1 40). 22-7 -227 Kumar & Associates LOGS OF EXPLORATORY PITS li1. 2 I SAMPLE OF: Very Silty Sond FROM:Pit2E^3' WC = 6.5 %, DD = 84 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING in thô {rìlt6n opprovol of 2 0 -2 -4 -6 -8 -10 -12 òe JJ t¡J =tn I z.otr ê =() tnzo(-) 100RE _ KSF 101.0I 22-7 -227 Kumar & Associates SWELL_CONSOLIDATION TTST RESULT Fig. 3 ú roo 90 80 7Ð 60 50 40 30 10 o HYOROMETER ANALYSIS SIEVE ANALYSIS ÎIUE READINGS 2¿ HRS 7 HRS tMtñ U.S. STANDARÐ SERIES OPENINGS 1 I j I I T ,jr, Ì i l I '.; tit o 10 20 30 40 50 60 70 ao 90 fm I I .o02 ,t50 ts -125 2.O MILLIMEÏERS t52 DIAMETER OF PARTI CLAY TO SILT COBBLES GRAVEL A3 % SAND LIQUID LIMIT SAMPLE OF: Sondy Grov€l wilh Cobbles 16 % PLASTICITY INDEX SILT AND CLAY 1 % FROM:Pil 1@4'-5' fheso lorl.6suliË opply only lo lhe somplos wh¡ch wêre t€slod. Th€ lesllng roport sholl not b€ roproduced, oxcspt in full, wlthoul lh€ wrlll€n qpprovol of Kumor & Agggc¡olos. lnc. Sleve onolysls lesllng ls perlormsd ln occordoncã wllh ASTM 06913, ASTM 07928, ASÍM Ct56 ondlor ASTM Dltito. GRAVELSAND MEDTUM lcornsE FINE COARSEFINE Fig. 4GRADATION TEST RTSULTS22-7 -227 Kumar & Associates lGrtffi*ftffifffiniy;-." :t TABLE,I SUMMARY OF LABORATORY TEST RESULTS LIMITSGRADATIOI{SAMPLE LOCATION SOIL TYPÊLIQUID LIMIT tî/^l IOA\ PLAS'ttC INDEX UNCONFINED COMPRESSIVE STRENGIH lôrJl NATURAL DRY DENSTfY GRAVEL l%l SAND (%l PERC€NT PASSING NO. 200 srEvE Ptf fft) DEPTH NATURÂL MOISTURE CONTENT Very Silty Sand8538I212.3 Sandy Gravel with Cobbles83t64-5 Very Silty Sand6.5 8423 Very Silty Sand3.7 835 No.