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Home My WebLink AboutSubsoil Studyl*rtiiçl[#'1'fËtrn"1Ëü*'*5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com www.kumarusa.comAn Employcc O,vncd Compony Office Locations: Denver (HQ), Parke¡ Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado RECEIVED JAN 3 I 2022 GARFIELD COUNTY COMMUNITY DEVELOPMENT SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 6, GTLEAD GARDENS GARDEN CIRCLE GARFIELD COUNTY, COLORADO PROJECT NO.21-7-581 AUGUST 20,2021 PREPARED FOR: LISA BRISCOE P.O. BOX 414 NEW CASTLE, COLORADO 81647 lisa.elementph@smail.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION SITE CONDITIONS FIELD EXPLORATION SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS ..... DESIGN RECOMMENDATIONS ..... FOI-INDATIONS FOUNDATION AND RETAINING WALLS FLOOR SLABS UNDERDRAIN SYSTEM LIMITATIONS FIGURE I - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 &, 5 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1 . SUMMARY OF LABORATORY TEST RESULTS _1- -2- I 1 3- _?- .....................- 3 - 4-_\- _Á- 7- ..-7 - Kumar & Associates, lnc. @ Project No. 21-7-58'l PURPOSE AND SCOPE OF'STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 6, Gilead Gardens, Garden Circle in Garfield County, Colorado. The project site is shown on Figure 1. The purpose of the study was to develop recommendations for foundation design. The study was conducted in accordance with our agreement for geotechnical engineering services to Lisa Briscoe dated June 16,2021. A field exploration program consisting of two 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 analyzed to develop recommendations for fðundation types, depths and allowable pressures for the proposed building foundation. This report summarizes the data obtained during this study and presents our conclusions, recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. A Preliminary Geotechnical Study was performed by Hepworth-Pawlak Geotechnical, Inc. (now Kumar & Associates) for the Gilead Gardens Subdivision and the results were presented in a report dated December29,2000, Job No. 100 672. Pert\nent information from the previous geotechnical study was used in preparation of this report. PROPOSED CONSTRUCTION The proposed residence will be a single-story structure above a walkout basement with an attached three car garage. We assume the basement and garage floors will be a slab-on-grade. At the time of our study, grading plans had not been developed. Grading for the structure is assumed to be relatively minor with cut depths up to about 6 feet. Based on the site grades, there could be fill placed below the garage and driveway arca. We assume relatively light foundation loadings, typical of the proposed type of construction. If building loadings, location or grading plans are significantly different from those described above, we should be notified to re-evaluate the recommendations contained in this report. SITE CONDITIONS The subject site was vacant at the time of our field exploration. The ground surface is sloping down to the north ranging ftom2 to 8 degrees. The slope varies between about 5 to 15 degrees Kumar & Associates, lnc. @ Project No. 21-7-581 -2- uphill to the south near the cul-de-sac. A dry irrigation ditch traverses the southern side of the building envelope and trends east-northeast. We understand the ditch is not in use and will be backfilled as part of construction. A flowing irrigation ditch roughly follows the western and northern property lines. The ground surface is covered with scattered grasses, weeds and crop remnants. F'IELD EXPLORATION The field exploration for the project was conducted on July 16, 202I. Two exploratory borings were drilled at the approximate locations shown on Figure I to evaluate the subsurface conditions. The borings were advanced with 4-inch diameter continuous flight auger powered by a truck-mounted CME-458 drill rig. The borings were logged by a representative of Kumar & Associates, Inc. Samples of the subsoils were taken with 1%-inch and 2-inch 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 profiles encountered at the site are shown on Figure 2. Below about 6 inches of topsoil, the subsoils consist of interlayered slightly sandy to very sandy clay and silt containing gravel at depth underlain in Boring 1 by very dense silty, sandy gravel with cobbles at a depth of about 2l feet. Gravel was not encountered in Boring 2 within the maximum explored depth of 21 feet. The soils encountered in the borings are similar to the soils encountered in the December 2000 geotechnical study. The clay portions of these soils can possess an expansion potential when wetted. Laboratory testing performed on samples obtained during the field exploration included natural moisture content and density, percent clay and silt-sized particles passing the No. 200 sieve, and swell-consolidation. Swell-consolidation testing was performed on relatively undisturbed drive samples of the clay and silt subsoils. The swell-consolidation test results, presented on Figures 4 and 5, indicate low to moderate expansion potential when wetted under a constant light surcharge. The laboratory testing is summarized in Table 1. Kumar & Associates, lnc. @ Project No. 21-7-58'l -J- No free water was encountered in the boreholes at time of drilling. The subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS The subsoils encountered at the site possess low to moderate expansion potential when wetted. The expansion potential can probably be mitigated by load concentration to reduce or prevent swelling in the event of wetting below the foundation bearing level. Surface runoff, landscape irrigation, and utility leakage are possible sources of water which could cause wetting. Altematively, potential movement can be reduced by methods such as removing and replacing the bearing soils as compacted structural fill or micro-piles down into the gravel soils. Acceptable fill materials are discussed below in the "Foundation and Retaining Walls" section of this report. DESIGN RECOMMENDATIONS FOLINDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the residence be founded on 1) spread footings with a minimum dead load pressure placed on undisturbed natural soils, or 2) spread footings with no minimum dead load placed on a minimum of 3 feet of compacted structural fill below garage and basement/crawlspace footings. If a deep foundation is desired to achieve a low movement risk, we should be contacted for additional recommendations. The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed on the undisturbed natural soils can be designed for an allowable bearing pressure of 2,500 psf and a minimum dead load pressure of 800 psf. In order to satis$ the minimum dead load pressure under lightly loaded areas, it may be necessary to concentrate loads by using a grade beam and pad system. Wall- on-grade construction is not recommended at this site to achieve the minimum dead load. Alternatively, footings placed on a minimum of 3 feet of moisture- conditioned and compacted structural fill can be designed for an allowable bearing pressure of 2,500 psf and no minimum dead load. 2) Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be up to about I inch. There could be additional movement of around 1 inch if the bearing soils were to become wet. Kumar & Associates, lnc. o Project No. 21-7-581 -4- 4) The footings should have a minimum width of 16 inches for continuous footings and24 inches for isolated pads. Continuous foundation walls should be reinforced top and bottom to span local anomalies and limit the risk of differential movement. One method of analysis is to design the foundation wall to span an unsupported length of at least 12 feet. Foundation walls acting as retaining structures should also be designed to resist a lateral earth pressure as discussed in the "Foundation and Retaining Walls" section of this report. 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 the exterior grade is typically used in this area. Prior to the footing construction, any existing fill, topsoil and loose or disturbed soils should be removed and the footing bearing level extended down to competent bearing soils. Structural fill such as CDOT Class 6 base course should be compacted to at least 98Yo of standard Proctor density and extend beyond the footing edges a distance at least equal to one-half the depth of fill below the footing. A representative ofthe geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. 5) 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 fine-grained soils and at least 45 pcf for backfill consisting of imported granular materials. Cantilevered retaining structures which are separate from the residence and can be expected to deflect sufficiently to mobilize the full 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 45 pcf for backfill consisting of the on-site fine-grained soils and at least 40 pcf for backfill consisting of imported granular materials. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The 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 3) 6) 7) Kumar & Associates, lnc. @ Project No. 21-7-581 5 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 90% of the maximum standard Proctor density at a moisture content near optimum. Backfill placed in pavement or structural areas should be compacted to at least 95Yo 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. 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. 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 the footings can be calculated based on a coefficient of friction of 0.35 for on-site fine-grained materials or 0.50 for imported granular materials. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 325 pcf for on-site fine-grained materials or 400 pcf for imported granular materials. 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 ofpassive resistance. FLOOR SLABS The natural clay soils possess an expansion potential and slab heave could occur ifthe subgrade soils were to become wet. Slab-on-grade construction may be used provided precautions are taken to limit potential movement and the risk of distress to the building is accepted by the owner. A positive way to reduce the risk of slab movement, which is commonly used in the area, is to construct structurally supported floors over crawlspace. To reduce the effects of some differential movement, nonstructural floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestrained vertical movement. Interior non-bearing partitions resting on floor slabs should be provided with a slip joint at the bottom of the wall so that, if the slab moves, the movement cannot be transmitted to the upper structure. This detail is also important for wallboards, stairways and door frames. Slip joints which will allow at least 1%-inches of vertical movement are recommended. Floor slab control joints should be used to reduce damage due to shrinkage Kumar & Associates, lnc. o Project No. 2l-7-581 -6- cracking. Slab reinforcement and control joints 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 immediately beneath basement level slabs-on-grade. This material should consist of minus 2-inch aggregate with less than 50%o passing the No. 4 sieve and less than 2o/o passing the No. 200 sieve. The free-draining gravel will aid in drainage below the slabs and should be connected to the perimeter underdrain system. Required fill beneath slabs should consist of suitable imported granular material, excluding topsoil and oversized rocks. The fill should be spread in thin horizontal lifts, adjusted to near optimum moisture content, and compacted to at least 95%o of the maximum standard Proctor density. All vegetation, topsoil and loose or disturbed soil should be removed prior to fill placement. The above recommendations will not prevent slab heave if the expansive soils underlying slabs- on-grade become wet. Howevero the recommendations will reduce the effects if slab heave occurs. All plumbing lines should be pressure tested before backfilling to help reduce the potential for wetting. I.INDERDRAIN SYSTEM Although groundwater was not encountered during our exploration, it has been our experience in the area and where clay soils are present, that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched condition. Therefore, we recommend below-grade construction, such as crawlspace and basement areas, be protected from wetting by an underdrain system. The drain should also act to prevent buildup of hydrostatic pressures behind foundation walls. The underdrain system should consist of a drainpipe surrounded by free-draining granular material placed at the bottom of the wall backfill. The drain lines should be placed at each level of excavation and at least I foot below lowest adjacent finish grade, and sloped at a minimum l%o grade to a suitable gravity outlet. Free-draining granular material used in the drain system should consist of minus 2-inch aggregate with less than 50Yo passing the No. 4 sieve and less than2%o passing the No. 200 sieve. The drain gravel should be at least IYz feet deep. Void form below the foundation can act as a conduit for water flow. An impervious liner, such as 20 mil PVC, should be placed below the drain gravel in a trough shape and attached to the foundation wall above the void form with mastic to keep drain water from flowing beneath the wall and to other areas of the building. Kumar & Associates, lnc. @ Project No. 21-7-58'l -7 - SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Excessive wetting or drying of the foundation excavations and underslab areas should be avoided during construction. Drying could increase the expansion potential of the soils. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95%o of the maximum standard Proctor density in pavement areas and to at leastg}Yo of the maximum standard Proctor density in landscape areas. Free- draining wall backfill should be capped with about 2 to 3 feet of the on-site soils to reduce surface water infiltration. 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 frrst l0 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy inigation 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 excavated at the locations indicated on Figure l, 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. Ifthe 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 to be different from those described in this report, we should be notified at once so re-evaluation of the recommendations may be made. Kumar & Associates, lnc. @ Project No. 21-7-581 -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 consfuction 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 of 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. Respectfu lly Submitted, Kumar & AssociatesrÍie. r,ø/â# Mark Gayeski, E.I.T. Reviewed by: Steven L. Pa MG:SLP/kac Cc: Brad Jordan l.com Kumar &,Associates, lnc. o Project No. 21-7-581 BORING BORING s TO ct 1 APPROXIMATE SCALE-FEET 21 -7 -581 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 BORING EL.55r ,| 7' BORING 2 EL. 5521' 0 0 33/12 32/12 5 16/ 12 WC=6.2 DD= 1 05 22/12 WC=4.8 DD=115 -200=56 22/12 WC=6.2 DD=1 1 1 23/ 12 WC=6.2 DD='l f 5 5 21 /12 10 '10 26/12 WC=5.0 DD=1 1 0 -2OO=75 l-t¡J L¡Jt! I-FfLtdo 15 15 FL¡l LJL I-FfL LJo 24/12 3s/12 WC=6.0 DD=114 20 27 /12 20 21 /12 25 25s4/6 50 30 21 -7 -581 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 E. "^3Ìl I LEGEND TOPSOIL; CLAY, SANDY, SILTY WITH TRACE GRAVEL' ROOTS & ORGANICS, SOFT, SLIGHTLY MOIST TO MOIST, TANISH_BROWN. INTERLAYERED CLAY AND SILT (CL-ML); SLIGHTLY SANDY TO VERY SANDY, SHALLOW ROOTS, INCREASED GRAVEL WITH DEPTH, TRACE POROSITY AND TRACE TO SLIGHT CALCAREOUS, VERY STIFF TO HARD, SLIGHTLY MOIST TO MOIST, TAN TO DARK TAN AND LIGHT BROWN. GRAVEL (cM); S|LTY, SANDY WITH COBBLES, VERY DENSE, SLIGHTLY MOIST, LIGHT GRAYISH- TAN. DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE i DR|VE SAMPLE, r 5/8-|NCH l.D. SPLIT SPOON STANDARD PENETRATION TEST ,2,A^ DRIVE SAMPLE BLOW COUNT' INDICATES THAT 35 BLOWS OF A 14o_POUND HAMMERrrl tz FALLTNG Jo TNCHES WERE REQU|RED To DRtvE THE SAMpLER t2 tNcHES. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JULY 16, 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 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 (pcf) (ASTM D2216); -2OO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM 01140). 21 -7 -581 Kumar & Associates LEGEND AND NOTES Fig. 3 SAMPLE OF: Sondy Cloyey Sìlt FROM:Boringl@5' WC = 6.2 "/", DD = 105 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING \ I ) ñ JJ LJ =tn I zo t- ô =o anzo(J 1 0 1 2 -3 -4 I 1.0 ÂPPLIEO 100 à( JJ l¡J =(n I z.o F âfo anzoo 2 1 o 1 -2 -3 APPLIED PRESSURE - KSF f0 t00 SAMPLE OF: Sondy Silty Cloy FROM: Boring 1 @ 10' WC = 6.2 "Á, DD = 1,l1 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING I ¡ 21 -7 -581 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4 E I I 3 2 f 0 -1 -2 -3 2 1 o -1 x JJ l,¡l =(n I zo t- ô =o(nzo(J JJ L¡J =Ø I zot- o Jo UIzo C) 100- KSF t01.0 APPLIED SAMPLE OF: Slightly Sondy Silty Cloy FROM:Boring2@5' WC = 6.2 %, DD = 115 pcf (EXPANSION UNDER CONSTANT PRESSURE UPON WETTING \\ I ) SAMPLE OFr Slightly Sondy Silty Cloy FROM:Boring2@15' WC = 6,0 "/", DD = 1 14 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING > ) I \ ft.m þd rurultr oÞPly only b ü6 hmpl.r tcdd. ñ. t6tting rêPod ftoll nd b roøoduccd, .rc.Pt In full, f¡thout úc rát.n opÞ'trl ol Kumor ond þE¡úr, lñc. Stlll Conloliddion t lting Fffomed in ôæôrddñcè dth m D-4546. -2 1.0 Fig. 5SWELL_CONSOLIDATION TEST RESULTSKumar & Associates21 -7 -581 I l(+ltä'ffi l['ffi,#snilf'å*'" :t TABLE 1 SUMMARY OF LABORATORY TEST RESULTS GRADATION ßAì PLASÍIG INDEX lbrll uNcol{Fll{ED c0tPRESstvE STRENGIH SOIL TYPÊGRAVEL (%) SAND (%) PERCEIIf PASSI{G NO. 200 stEvE LIQUID LIIIIT t%l BORING tf0 DEPTH I{ATURAL TOISTURE coNTEt{l loc0 NATURAL DRY DENSIW Sandy Clayey Silt56.2 105I Slightly Clayey Very Sandv Silt567%4.8 ll3 Sandy Silty Clay6.2 llll0 Slightly Sandy Silty Clayll5256.2 Slightly Clayey Sandy Silt75105.0 110 Slightly Sandy Siþ Clay156.0 rl4