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HomeMy WebLinkAboutSubsoil StudyI (aJf iiffii[ffif¡$i*'"'Ë;' **' An Employcc Onrncd 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 t¡cations: Dørver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE TBD CÄ.TTLE DRIVE TRACT 43 ANTLERS ORCHARD DEYELOPMENT GARFIELD COUNTY, COLORADO PROJECT NO.22-7-122 FEBRUARY 24,2022 PREPARE,D FOR: JESSE F'LOWERS LTI?BALLARD AVENUE SILT, COLORADO 81652 (eambit2248@Yahoo ) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS....... FIELD EXPLORATION SUB SURFACE CONDITIONS . FOUNDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS FLOOR SLABS I.INDERDRAIN SYSTEM ........ SITE GRADING. SURFACE DRAINAGE LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1 - STJMMARY OF LABORATORY TEST RESULTS I 1 1 1 -2- 1 J J 4 4 4 5 ..-5- Kumar & Associates, lnc. @ Project No.22-7-122 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located at TBD Cattle Drive, Truct 43, Antlers Orchard Development, Garfield County, Colorado. The project site is shown on Figure 1. The pu{pose 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 Jesse Flowers dated January 14,2422. A field exploration program consisting of exploratory borings was conducted to obtain information on the subsurface conditions. Samples of the subsoils and bedrock 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 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 be a one to two-story, wood-framed structure over a crawlspace with a slab-on-grade garage floor. Grading for the structure is assumed to be relatively minor with cut and fill depths between about 3 to 5 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 recoÍtmendations contained in this report. SITE CONDITIONS The site was vacant and had a few inches of snow cover at the time of our site visit. The proposed building footprint is located on a relatively natural hillside with a graded access trail. The ground surface is covered with scattered grasses, weeds, sage brush and juniper trees and, in general, moderately to steeply sloping down to the west, south and southeast. Steeper slopes are present further uphill to the north. Inside the building footprint area, the slope is moderately to strongly sloping down to the southwest. Kumar & Associates, lnc. o Project No.22-7-122 a FIELD EXPLORATION The field exploration for the project was conducted on January 25,2022. 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 and bedrock were taken with l%-inch and 2-inchl.D. spoon samplers. The samplers were driven into the subsurface materials 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 and hardness of the bedrock. 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. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils, below about I foot of organic sandy, silty clay, consisted of about lYzto 2 feet of firm sandy siþ clay and medium dense clayey sand with gravel. The subsoils were underlain at depths of 2%and 3 feet by medium hard to very hard siltstone and claystone bedrock. Laboratory testing performed on samples obtained from the borings included natural moisture content, Atterberg limits, and swell-consolidation. Results of swell-consolidation testing performed on a relatively undisturbed drive sample, presented on Figure 4, indicate no expansion and relatively low compressibility under conditions of loading and wetting. The laboratory testing is summarizedinTable 1. No free water was encountered in the borings at the time of drilling and the subsoils and bedrock were slightly moist to moist. F'OUNDATION BEARING CONDITIONS The upper sand and clay soils possess a low bearing capacity and a low settlement or expansion potential if wetted. Testing indicates the underþing claystone/siltstone bedrock is non-expansive and has low compressibility potential. Shallow spread footings placed entirely on the bedrock can be used for support of the proposed residence with a low risk of foundation movement' We Kumar & Associates, lnc. @ Project No.22-7-122 -3 - should observe the subsurface conditions exposed at the time of excavation and evaluate them for swell-compression potential and possible mitigation. Proper surface drainage as described in this report will be critical to the long-term satisfactory performance of the structure. 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 on spread footings bearing on the natural bedrock. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural bedrock should be designed for an allowable bearing pressure of 3000 psf. Based on experience, we expect settlement or heave 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 24 inches for isolated Pads. 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 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 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 onsite soils as backfill. 5) The topsoil and any loose or disturbed soils should be removed and the footing bearing level extended down to the relatively hard bedrock. The exposed soils in footing area should then be moistened and compacted. We should evaluate the exposed bedrock for expansion potential and the need for subexcavation and placement of structural frllfor movement mitigation. 6) A representative ofthe geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. Kumar & A¡sociates, lnc. o Project No.22-7-122 -4- FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction with a risk of movement. To reduce the effects of some differential movement, floor slabs should be separated from all bearing walls and columns with expansionjoints 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 free-draining gravel should be placed beneath slabs to facilitate drainage. This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve and less than?Yo passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95Vo of maximum standard Proctor densþ 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 Atthough free water was not encountered during our exploration, it has been our experience in the area and where bedrock is shallow 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 construction, such as retaining walls, crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain 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 IYo to a suitable gravity outlet. Free-draining granular material used in the underdrain system should contain less than 2Yo passingthe No. 200 sieve, less than 50olo passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least lYzfeet deep. SITE GRADING The risk of construction-induced slope instability at the site appears low provided the building is located in the less steep slope area as planned and cut and fill depths are limited. 'We assume the cut depths for the crawlspace level will not exceed about 3 to 5 feet. Difficult excavation in the bedrock should be anticipated. Fills should be limited to about I feet deep. Embankment fills should be compacted to at leastg5Yo of the maximum standard Proctor density near optimum Kumar & Aseociates, lnc. @ Project No.22-7-122 5 moisture content. Prior to fill placement, the subgrade should be carefully prepared by removing all vegetation and topsoil and compacting to at least 95Yo of the maximum standard Proctor density. The fill should be benched into the portions of the hillside exceeding 20Yo grade. Permanent unretained cut and fill slopes should be graded at2horizontal to I vertical (2H:lV) or flatter and protected against erosion by revegetation or other means. SURFACE 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 backfrll 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 90Vo 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. Free-draining wall backfill should be covered with frlter fabric and 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 irrigation should be located at least 5 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 concerned about MOBC, then a professional in this special field of practice should be consulted. Our findings include interpolation and extrapolation of the Kumar & Associales, lnc. o Project No.22-7-122 -6- 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 veriry that the recommendations have been appropriatelyinterpreted. 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. Respectfirlly Submitted, Kumar & Associates, Inc. %/fu Mark Gayeski, E.I.T. Reviewed by: Steven L. Pawlak, SLP/kac Cc: J. Caliber ( i ose(grj caliberconstruction. com) Kumar & Associates, lnc. o Project No.22-7-122 d r--7.¿ ' -Y+r¡{.t 9J È T Orct ¿b ð'Þa Com¡nn Receptr ¿ \ T'l 45,O'Ac Rece,I t î6,ì.1 b Ft E U) f---- t-- I I \\ : \ Antlers Qn Campa Reæpl\ \,,l L 0 o APPROXIMATE SCALE-FEET 99SLG-1, Aøes' BORING I I I \ utatr\ \ I 43 22-7-122 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING 1 BORING 2 o 0 3s/6,50/4 WC=5.6 DD= 1 28 LL=25 Pl=10 23/6, 50/4 5 5 87/12 43/12 WC=7.5 LL=36 Pl=19 10 10 l-IJtljlÀ Ift-fLl¡lô 5a/4 80/12 WC=9.1 DD=1 1 I !- L¡Jt¡lI! I-f-(L t¡lo 15 15 so/5 50/3 20 20 50/2.s 25 25 Fig. 2LOGS OF EXPLORATORY BORINGSKumar & Associates22-7-122è ¿ N I È ¿ LEGEND N TOPSOIL: ORGANIC SANDY SILTY CLAY, FIRM, SLIGHTLY MOIST, LIGHT BROWN TO TAN SAND (SC): CLAYEY W|TH GRAVEL, MEDIUM DENSE, SLIGHTLY MOIST, TAN, ROOTS. CLAY (CL): SANDY, SILTY, FIRM, SLIGHTLY MOIST, GRAYISH-TAN Át/CLAYSTONE AND SILTSTONE BEDROCK: INTERLAYERED, SLIGHTLY SANDY WITH OCCASIONAL SHALLOW THIN SANDSTONE LENSES, MEDIUM HARD TO VERY HARD WITH DEPTH, SLIGHTLY MOIST TO MOIST, GRAYISH_TAN TO GRAY. F i DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE. DRTVE SAMPLE, 1 s/1-lNcH l.D. SPLIT-SPOON STANDARD PENETRATION TEST 87 /12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 87 BLOWS OF A l4O_POUND HAMMER FALLING 50 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 25, 2O2Z WITH A 4-INCH DIAMETER CONTINUOUS_FLIGHT POWER AU6ER. 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 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: V"C = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (PCf) (ASTM D2216); LL = LIQUID LIMIT (ASTM DA518); Pl = PLASTICITY INDEX (ASTM D4518). 22-7-122 Kumar & Associates LEGEND AND NOTES Fig. 5 Ë I SAMPLE OF: Cloystone/Siltstone FROM: Boring 2 @ 10' WC = 9.1 26, DD = lf I pcf NO MOVEMENT UPON WETTING ¡nd h 1 ¡t )J l¡J =ar', I z.otr o =() vlz.o(J 1 2 5 4 -5 PRESSURE -t00 FTg. 4SWELL_CONSOLIDATION TTST RESULTSKumar & Associates22-7-122 lGrt[ffii[ffi:ffi*iiiå**TABLE 1SUMMARY OF LABORATORY TEST RESULTSClaystone/SiltstoneSOILTYPEClaystone/SiltstoneClaystone(psflUNCONFINEDCOMPRESSIVESTRENGTHt9(o/olPLASTICINDEX1025{%)LIQUID LIMIT36ATTERBERG LIMITSPERCENTPASSING I{0.200 stEvEiloNSANDli/"\(%)GRAVEL128118NATURALDRYDENSITYlocf)I9lololNATURALMOISTURECONTENT3.67.5501{ft}DEPTH2v,12SAMPI.E LOCATIONBORINGNo.22-7-122