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Home My WebLink AboutSubsoils Report for Foundation DesignKtnf$ffir*-i** An Emdoyas Ownsd CsmpEny 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa.com Offrce Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 5, FOUR MrLE RANCH 450 RED CLIFF CIRCLE GARFTELD COUNTY, COLORADO PROJECT NO. 21-7-906 FEBRUARY 2,2022 PREPARED FOR: CEFERINO HERRERA P.O. BOX 373 SILT, COLORADO 81652 westerndrywallstucco@outlook.com EIE\I.+EI cv:lht +l&t trE -trl =3IEE --l-|ft ulH -Ell - l'Jt-l 15 va'ElE ..- #lE = _-t-HIF! ur E.]E = _t_ -lF - =IE E TABLE OX'CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION .. SITE CONDITIONS... FIELD EXPLORATION SUBSURFACE CONDITIONS ... FOUNDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS ...... FOI-]NDATIONS FOUNDATION AND RETAINING WALLS FLOOR SLABS {-INDERDRAIN SYSTEM ............. 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- SUMMARY OF LABORATORY TEST RESULTS .-2- .-2- ...- 2 - J- J J 4 5 6 6 -7 - I I Kumar & Associates, lnc. @ Project No. 2l-7-906 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 5, Four Mile Ranch, 450 Red Cliff Circle, 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 Ceferino Herrera dated December 5,2021. 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, 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 assumed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The design for the proposed residence had not been determined at the time this report was prepared, but is assumed to be a one- and two-story wood frame structure located in the building envelope shown on Figure 1. Ground floors could be slab-on-grade or structural above crawlspace. Grading for the structure is assumed to be relatively minor with cut depths between about 4 to l0 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans differ significantly from those described above, we should be notified to re-evaluate the recommendations contained in this report. Kumar & Associates, lnc, @ Project No. 21-7-906 .| -L' SITE CONDITIONS The site was vacant at the time of our field exploration, and was covered with I to 2 feet of snow. The lot slopes gently to moderately down to the west and northwest, with little change in elevation across the building envelope. Vegetation consists of sage brush, grass and weeds. FIELD EXPLORATION The field exploration for the project was conducted on December 29,2021. 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-45B drill rig. The borings were logged by a representative of Kumar & Associates, Inc. Samples of the subsoils were taken with a 2-inch I.D. Califomia type liner 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 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 encountered, below about 1 foot of topsoil, consist of between about 6 to 9% feet of stiff to very stiff, sandy silty clay overlying relatively dense, silty sandy gravel with cobbles and probable boulders down to the maximum drilled depth of 13% feet. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and probable boulders and drilling refusal was encountered in the deposit in both borings. Laboratory testing performed on samples obtained from the borings included natural moisture content, density, and percent finer than sand size gradation analyses. Results of swell- consolidation testing performed on relatively undisturbed drive samples of the clay soils, Kumar & Associates, lnc. @ Project No.21-7-906 -3- presented on Figure 4,indicate low compressibility under light loading and a low swell potential when wetted. The laboratory testing is summarizedin 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 soils exhibit a low expansion potential when wetted that could result in post- construction building movement or distress. Care should be taken in the surface and subsurface drainage around the house to prevent clay bearing soils from becoming wet. It will be critical to the long-term performance of the structure that the recommendations for surface grading and subsurface drainage contained in this report be followed. The amount of movement will mainly be related to the depth and extent of subsurface wetting of the clay soils. Extending the foundation bearing levels down to the granular soils or replacing the clay soils with at least 2 feet of compacted structural fill could be provided to achieve a lower risk of differential movement and distress. 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 or on compacted structural fill bearing on the natural granular soils. The expansion potential of the clay soils exposed at design bearing level should be evaluated for sub-excavation and replacement with compacted structural fill. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed soils or compacted structural fill should be designed for an allowable bearing pressure of 2,000 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this Kumar & Associates, lnc. @ Project No. 21,7-906 -4- 2) section will be about 1 inch or less with around%to 1 inch of post-construction settlement depending on the bearing soil and wetting conditions. The footings should have a minimum width of 16 inches for continuous walls and 2 feet 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 below exterior grade is typically used in this atea. 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 lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. The topsoil, expansive clay soils, and any loose or disturbed soils should be removed and the footing bearing level extended down to the firm natural soils. The exposed soils in footing area should then be moistened and compacted. If needed, structural filI consisting of 3/+-inch road base can be placed and compacted in thin lifts to at least 98% of the maximum standard Proctor density at a moisture content near optimum to re-establish design footing bearing grades. A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. 3) 4) s) FOUNDATION AND RETAINING WALLS Foundation walls and retaining structures which are laterally supported and can be expected to undergo only a slight amount of deflection should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting of the on-site soils. Cantilevered retaining structures which are separate from the residence and can be expected to deflect sufficiently to mobilize the fulI active earth pressure condition should be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight of at least 50 pcf for backfill consisting of the on-site soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The 6) Kumar & Associates, lnc. @ Project No. 21-7-906 -5- pressures recommended above assume drained conditions behind the walls and a horizontal backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfill should be placed in uniform lifts and compacted to at least 90Yo of the maximum standard Proctor density at a moisture content near optimum. Backfill placed in pavement and walkway areas should be compacted to at least 95Vo of the maximum standard Proctor density. Care should be taken not to overcompact the backfill or use large equipment near the wall, since this could cause excessive lateral pressure on the wall, and increase expansion potential of clay soils used as backfill. Some settlement of deep foundation wall backfill should be expected, even if the material is placed correctly, and could result in distress to facilities constructed on the backfill. Backfill should not contain organics, debris or rock larger than about 6 inches. The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of footings placed on the natural granular soils or on compacted structural fill can be calculated based on a coefficient of friction of 0.45, and a coefficient of friction of 0.30 for footings placed on the clay soils. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The coefficient of friction and passive pressure values recommended above assume ultimate soil strength. Suitable factors of safety should be included in the design to limit the strain which will occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be compacted to at least 95Yo of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS Lightly loaded slab-on-grade construction placed on the clay soils will have a risk of movement and distress. We recommend at least 2 feet of granular soil such as road base be placed below slabs in clay soil areas. 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 Kumar & Associates, lnc. @ Project No. 21-7-906 -6- 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 basement level 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 than2o/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 should consist of granular soils devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM Although free water was not encountered during our exploration, it has been our experience in the area and where there are clay soils 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 or sump and pump. Free-draining granular material used in the underdrain system should contain less than 2%o passing the 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 llz feet 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. Kumar & Associates, lnc. @ Project No.21'7-906 -7 - 3) 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 90o/o of the maximum standard Proctor density in landscape areas. 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 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 filter fabric and capped with about 2 feet of the on-site soils to reduce surface water infiltration. Roof downspouts and drains should discharge well beyond the limits of all backfill. Landscaping which requires regular heavy inigation and sprinkler heads 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 inigation. 4) LIMITATIONS This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this arca 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 assumed 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 2) s) Kumar & Associates, lnc. @ Project No, 21-7-906 -8- msnitor the implcmentation cf our r€oornmendations, and to vcri$ that ths recofilme*dations have been appropriately interpreted. Significant design changes may require additicnal analysis or m*difications to the recomrnendations presented herein. We recommend on-site abservation cf ex*avations and fcundation bearing strata and testing of struct*ral fill by a representative of the geoteelinical enginecr. Respectfully $ubmitted, Kaamar &,{ssoeiates, Ime" David A. Noteboom, Staff Engineer Reviewed By: Steven L. Pawlak, P.E sLPlljf 18222 Kumar & A*so*!atem, Bnc,6 FrCIisct hto.21"?-SSS i q TDon z.o ) {\ @on z. c) NF**ghl- b$D*{**o, t+ ""c0ry.lo *5l*L*p--{ r) !t {Jllf,# N** s$H ffims { I I t i @ 1 >@atlazco<-m<9>nx rrlt-rrts oq p C ,1ory *t n f.:9 8$fi hu*$# { ! / t} I "3bt") 'A I J II ;*",\ i Nhsil54sfi c! fflf*:i eil "*bh?I fntr* {} cas .et C} 4 <n ), N\ iwn " b;fi ilirt mA & -tJ'ft l LNo o UIo 1ltlnox -lrrl tn c) r-rrt I Irn rn--{ -e# N) I! I(oo Ot xc 3q) -l eo U, @oo. o) oa t-oc) -.{oz. oT] rnXTt-On -{on @on z. C) U) =(o BORING 1 EL. 96' BORING 2 EL. 96, o 0 13/ 12 WC=8.2 DD=88 -2QO=92 23/12 WC=9.6 DD= 1 03 5 5 l- UJut LL I-F(L trJo 27/12 WC=8.9 DD= 1 02 18/ 12 FulLI LL I-F(L tdo 10 36/ 12 WC=7.1 DD=117 -200=60 10 15 15 21 -7 -906 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 I 3i LEGEND TOPSOIL; SILTY SANDY CLAY, ORGANICS, FIRM, MOIST, BROWN. CLAY (CL); SLIGHTLY SANDY TO SANDY, SILTY, STIFF T0 VERY STIFF, Mo|ST, LIGHT BROWN, SLIGHTLY TO MODERATELY CALCAREOUS, SLIGHT POROSITY, LOW TO MEDIUM PLASTICITY. GRAVEL (GM); COBBLES AND PROBABLE BOULDERS, SANDY, SLIGHTLY SILTY, DENSE TO VERY DENSE, SLIGHTLY MOIST, LIGHT GRAY AND TAN. DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE. 42 t.6 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 13 BLOWS OF A 140-POUND HAMMERtr/ tz FALLTNG Jo TNCHES wERE REeU|RED To DRtvE THE sAMPLER 12 tNcHES. f enlcrcAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON DECEMBER 29,2021 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 MEASURED BY INSTRUMENT LEVEL AND REFER TO THE SEWER MANHOLE COVER ON RED CLIFF CIRCLE AS BENCHMARK WITH ELEVATION 1OO' ASSUMED. 4. THE EXPLORATORY BORING LOCATIONS 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 RESULTS: WC = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (PCt) (ASTV D2216); -2AO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM Dl140). 21 -7 -906 Kumar & Associates LEGEND AND NOTES Fig. 3 t & ti a 2 bq JJ lrJ =a/1 I zotr o Jo U)zo() 1 0 -1 2 -3 1,0 APPLIED PRESSURE - KSF t0 100 2 bq JJ LJ =VI I z.otr o =oazoO 1 0 -1 2 -3 1,0 APPLIED PRESSURE - KSF t0 100 SAMPLE OF: Sondy Cloy FROM: Boring 1 G) 5' WC = 8.9 %, DD = 102 pcf (EXPANSION UNDER CONSTANT PRESSURE UPON WETTING ) SAMPLE OF: Sondy Cloy FROM: Boring2@2.5' WC = 9.6 "1, DD = 103 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 21 -7 -906 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4 K+nmlmfmn-;-* TABLE 1 SUMMARY OF LABORATORY TEST RESULTS No, 21-7-906 Sandy Clay Slightly Gravelly Sandy Clay SOIL TYPE Slightly Sandy Clay Sandy Clay (psfl UNCONFINED COMPRESSIVE STRENGTH PLASTIC INDEX (%l ATTERBERG LIMITS ("/"1 LIQUID LIMIT 92 60 PERCENT PASSING NO. 200 stEVE SAND (/") GRADATION (/") GRAVEL (ocfl NATURAL DRY DENSITY 88 r02 103 r17I7 (ol NATURAL MOISTURE CONTENT 8.2 8.9 9.62% 01 (ft) DEPTH 2% 5 1 2 SAMPLE LOCATION BORING