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Home My WebLink AboutSubsoils Report for Foundation DesignlGrtf-ffi,ffiFH*1'#*-* An Employoc olrncd Conpony 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa.com Oftice locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit Cormty, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT H.16, ASPEN GLEN SADDLEBACK ROAD GARFTELD COUNTY, COLORADO PROJECT NO. 21.7.5I-9 AUGUST 10,2021 PREPARED F'OR: DOUG BUSS 219 GOLD DUST LANE MONTROSE, COLORADO 81403 @ TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY... PROPOSED CONSTRUCTION SITE CONDITIONS SUBSIDENCE POTENTIAL .......... FIELD EXPLORATION SUBSURFACE CONDITIONS FOUNDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS FOUNDATION AND RETAINING WALLS. FLOOR SLABS UNDERDRAIN SYSTEM ............. SURFACE DRAINAGE............... LIMITATIONS FIGURE I - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURE 4 . SWELL-CONSOLIDATION TEST RESULTS FIGURE 5 - GRADATION TEST RESULTS TABLE I- SUMMARY OF LABORATORY TEST RESULTS 1 1 1 a-L- .| -L- -J- 4 4 5 6 6 7 -7 - Kumar & Associates, lnc. @ Project No. 21-7-519 PURPOSE AND SCOPE OF STUDY This report presents the results ofa subsoil study for a proposed residence to be located on Lot H-l6, Aspen Glen, Saddleback Road, 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 Doug Buss dated June 8, 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 proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION Plans for the proposed residence were conceptual at the time of our study and will generally be a two-story structure with attached garage located on the site in the area of the borings shown on Figure 1. Ground floors will likely be a combination of structural over crawlspace for the living areas and slab-on-grade for the garuga Grading for the structure is assumed to be relatively minor with cut depths between about 2to 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 recommendations contained in this report. SITE CONDITIONS The subject site was vacant at the time of our field exploration. The subject site may have been partly graded as part of the original subdivision development. The ground surface slopes gently down to the northeast. Vegetation consists of grass and weeds. The golf course is west of the subject site. Kumar & Associates, lnc. @ Project No. 21-7-519 a SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanianage Eagle Valley Evaporite underlies the Aspen Glen development. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can produce areas of localized subsidence. During previous work in the arca, several sinkholes were observed scattered throughout the Aspen Glen Subdivision, mainly east of the Roaring Fork River. The nearest mapped sinkhole is about 2000 feet southeast of this lot. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the lower Roaring Fork River valley. Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities was encountered in the subsurface materials; however, 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 on Lot H-l6 throughout the service life of the proposed residence, in our opinion, is low; however, the owner should be made 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. F'IELD EXPLORATION The field exploration for the project was conducted on June21,202l. Two exploratory borings were drilled at the locations shown on Figure I 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 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-l586. 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. Kumar & Associates, lnc. @ Project No. 21'7-519 -J- SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils consist of about l%feetof topsoil overlying very stiff to hard, sandy clay to about 8 feet deep underlain by dense, slightly silty to silty sandy gravel and cobbles down to the maximum explored depth of 16 feet. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and probable boulders and drilling refusal was encountered at a depth of l2%feet in Boring 1. Laboratory testing performed on samples obtained from the borings included natural moisture content and density and gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed drive samples of the sandy clay, presented on Figure 4, indicate low compressibility under existing low moisture conditions and light loading and a low to moderate expansion potential when wetted under constant light surcharge. Results of a gradation analysis performed on small diameter drive samples (minus l%-inch fraction) of the coarse granular subsoils are shown on Figure 5. The laboratory testing is summarizedin Table 1. No free water was encountered in the borings atthe time of drilling and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The upper sandy clay soils encountered at the site typically possess a low bearing capacity and low to moderate expansion potential when wetted. The underlying gravel soils have a moderate bearing capacity and typically low settlement potential. Spread footings placed on the upper clay soils will have a risk of movement mainly if the bearing soils become wetted. We recommend the upper clay soils be removed from below footing areas to expose the underlying granular soils. Footings can be extended down to the underlying granular soils or the bearing grade can be reestablished with compacted structural fill. Alternatively, a basement level can be designed to bear entirely on the underlying gravel soils. Proper surface drainage should be provided around the residence to reduce the risk of subgrade wetting. Structural fill should consist of suitable granular material such as CDOT Class 6 base course moisture conditioned to near optimum moisture content and compacted to at least 98 percent of maximum standard Proctor density. The onsite granular soils could also be processed to remove oversized, plus 6-inch rock, and used as structural fill. Kumar & Associates, lnc. @ Project No. 21-7-519 -4- DESIGN RECOMMENDATIONS FOTINDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, we recommend the upper clay soils be removed from the building area andthe building be founded with spread footings bearing on the natural granular soils or compacted structural fill. The design and construction criteria presented below should be observed for a spread footing foundation system. 1)Footingsplacedontheundisturbednatura1granularsoi1sorry fill should be designed for an allowable bearing pressure of 2,500 psf. Footings igned 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 1 inch or less. 2) The footings should have aminimum width of 16 inches for continuous walls and 2 feet 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 afea. 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 lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. 5) Topsoil, sandy clay and any loose disturbed soils should be removed and the footing area excavation extended down to the relatively dense natural granular soils. The exposed soils in footing area should then be moistened and compacted. Structural fill to reestablish design bearing grade should be spread in thin horizontal lifts and compacted to at least 98 percent of maximum standard proctor density at near optimum moisture content. The fill should extend laterally beyond the footing edges a distance equal to at least one-half the depth of fill below the footing. Kumar & Associates, lnc. @ Project No.21-7-519 -5- A representative of the geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. FOTINDATION 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 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 soils. All foundation and retaining structures should be designed for appropriate hydrostatic and surcharge pressures such as adjacent footings, traffrc, 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 increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. Backfrll should be placed in uniform lifts and compacted to at least 90o/o of the maximum standard Proctor density at a moisture content slightly above optimum. Backfill placed in pavement and walkway areas should be compacted to at least 95%o 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 0.45. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 37 5 pcf. The coefficient of friction and passive pressure values recontmended 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 95o/o of the maximum standard Proctor density at a moisture content near optimum. 6) Kumar & Associates, lnc. @ Project No, 21-7'519 -6- FLOOR SLABS The natural on-site granular soils below topsoil and clay soils, are suitable to support lightly loaded slab-on-grade construction. We recommend at least 2 feet of structural fill be placed below slabs in clay soil areas to help mitigate the expansion potential. 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 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%o retained on the No. 4 sieve and less than 2%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 road base or the on-site granular soils devoid of vegetation, topsoil and oversized rock. We recommend vapor retarders conform to at least the minimum requirements of ASTMEI745 Class C material. Certain floor types are more sensitive to water vapor transmission than others. For floor slabs bearing on angular gravel or where flooring system sensitive to water vapor transmission are utilized, we recommend a vapor barrier be utilized conforming to the minimum requirements of ASTM 81745 Class A material. The vapor retarder should be installed in accordance with the manufacturers' recommendations and ASTM 81643. UNDERDRAIN SYSTEM Although free water 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. 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. Crawlspace areas shallower than about 4 feet should not need an underdrain provided exterior backfill is properly compacted and a positive surface slope is maintained away from the residence. Where installed, 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 Kumar & Associates, lnc. @ Project No.21-7-519 -7 - placed at each level of excavation and at least I foot below lowest adjacent finish grade and sloped at a minimumlYo to a suitable gravity outlet or drywell based in the underlying granular soils. Free-draining granular material used in the underdrain system should contain lessthan2%o passing the 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 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. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95o/o 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 arsas. 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 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. 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. 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 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 concemed 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 Kumar & Associates, lnc. @ Project No.21-7-519 -8- 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 recofirmendations, and to veriff that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recofirmendations 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, Kesxaqma" & Asss*6mf*su Ene, W-irt*-X, ?dqpr*ur James H. Parsons, P.E. Reviewed by: Steven L. Pawlak, P JHPlkac cc: RM (l*tr"ake{,&t?:u11&witWffi ,{fr ffi} Ir @ 18222 Wwm*r &Ass*ciates, nftc" d Pr*jee* 9-io, 2'l "?"$1 S EE}{C}IIIAR(: TOP OF lrAlil{Ol.E EL 100" ASSUHI0 BOR${6 2 t80Rlxe 21 -7 -519 Kumar & Associates LOCATION OF TXPLORATORY BORINGS Fig. 1 t BORING 1 EL. 104.4' BORI NG 02 2 6'EL.1 o o 3e/ 12 WC=8.1 DD=1 1 1 -200=81 30/ 12 WC=7.0 DD= 1 07 5 23/ 12 WC=9.2 DD= 1 08 22/12 WC=10.8 DD= 1 04 -2OO=92 40/6, 53/6 5 FtrlLIl! I-Fo-IJo 50/6 F LrJL]L- I-F(L bJo 10 10 50/4 50/6 15 1550/s 20 20 WC=0.5 +4=55 -200= 1 9 Fig. 2Kumar & Associates LOGS OF EXPLORATORY BORINGS21 -7 -519 ,s g g LEGEND N TOPSOIL; ORGANIC CLAY, SANDY, GRAVELLY, FIRM, SLIGHTLY MOIST, BROWN. CLAY (CL); SANDY TO VERY SANDY, VERY STIFF TO HARD, SLIGHTLY CLACAREOUS, SLIGHTLY MOIST, BROWN. Whj:tl l:iP] GRAVEL (0p-CU); SANDY, COBBLES, PROBABLE BOULDERS, SLIGHTLY SILTY TO SILTY, DENSE, SLIGHTLY MOIST, LIGHT BROWN. ROUNDED ROCK. DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE i DRTVE SAMPLE, 1 S/9-INCH l.D. SPLIT SPOON STANDARD PENETRATION TEST. ,^,.^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 59 BLOWS OF A 14o-POUND HAMMERrr/ tz FALLTNG J0 TNcHES wERE REQUIRED To DRtvE THE SAMPLER 12 lNcHES. f enacrcAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 21 , 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. 5. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY INSTRUMENT LEVEL AND REFER TO THE BENCHMARK ON FIG. 1. 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) (NSTV D2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTU OSSIS); -200= PERCENTAGE PASSING No. 200 SIEVE (ASTM Dl140). 21 -7 -519 Kumar & Associates LEGEND AND NOTES Fig. 3 t I$ t # tp I 5 2 1 0 1 -2 -3 \o 2 JJLI =anl I z.o U o =oa _lz.oo ts JJ trJ =a I z.otr o =otnzoo APPLIED PRESSURE - KSF APPLIED PRESSURE - KSF t0 10 100 r00 I 1.0 SAMPLE OF: Sondy Cloy FROM: Boring 1 G) 5' WC = 9,2 %, DD = 108 pcf ( EXPANSION UNDER CONSTANT PRESSURE UPON WETTING I \ I SAMPLE OF: Sondy Cloy FROM:Boring2@2.5' WC = 7.0 %, DD = 107 pcf \ he H 6ulu oPPt onlY b lhc romplc! tctrd. lh. tding ropod lholl not bG roprcaluc.d, .xccpl ln full, ulthout lhc rdtt.n opFFYol of (umor ond Asslob!, lnc, Sxall ionrolidotion tstlng p.rtodad ln rccordonc. *'ilh AsTll D-,t5,44. EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 21 -7 -519 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4 t|s HYDROMETER ANALYSIS U.S. S]ANDARD SERIES CLEAR SqUARE OPENINOS tle. ala. 1 tru' TIME READINOS I' HRS 7 HRS tuttr a" I E ro0 90 ao 70 80 50 10 to 20 to o o t0 20 50 & 50 50 70 ao 90 roo = E t ETER OF IN CLAY TO SILT COBBLES GRAVEL 33 % SAND LIQUID LIMIT SAMPLE OF: Sllty Sond ond Grovel 46% PLASTICITY INDEX SILT AND CLAY 19 % FROMr Borlng 2 o 7.5' & 10' (Comblnad) Th!8c lrsl rcrull! opply only lo lh6 somplcr whlch waro l.sbd. Thc l.sllnq roporl 8holl nol ba reprcduccd' cxcrpt ln full, wllhoul lhr yrlllrn opprcvol of Kumor & AEtoclql!!, lnc. Sl!v! onolyrls l.sllng h plrfomld ln occordoncc vlth ASTM D6915, ASTM D7928, ASTM Cl36 qnd/or ASTM D11,10. GRAVELSAND MEDIUM COARSE FINE COARSEFINE 21 -7 -519 Kumar & Associates GRADATION TEST RESULTS Fig. 5 l(+rt lfumar & Assncialm, lnn"@ Geolechnicsl and Material$ Engineers and Environmenlal Scientists TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Sandy Clay Slightly Sandy Clay Silty Sand and Gravel SOIL TYPE Sandy Clay Sandy Clay (psf) UNCONFINED COMPRESSIVE STRENGTH (%l PLASTIC INDEX ATTERBERG LIMITS (/"1 LIQUID LIMIT PERCENT PASSING NO. 200 stEVE 81 92 9146 (%) SAND 35 GRADATION ("/"1 GRAVEL 107 t04 (ocfl NATURAL DRY DENSITY 111 108 8.1 9.2 7.0 10.8 0.5 (%) NATURAL MOISTURE CONTENT (ft) DEPTH nt/ 5 2% 5 7% &, r0 combined SAMPLE LOCATION BORING 1 2 No. 21-7-519