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Home My WebLink AboutSubsoil StudyI C,* iffi f,ifffú:ff '""Êü' * * An Employos Ownad Compony 5020 Counfy Road 154 Glenwood Springs, CO 8l 60 I phone: (970) 945-7988 fax: (970) 945-8454 email : kaglenwood@kumarusa.com lwvr,v. kttrn arttsa. cor.n Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOIJNDATION DESIGN LOT M-26, ROARTNG FORK MESA AT ASPEN GLEN GOLDEN STONE GARFIELD COUNTY, COLORADO PROJECT NO.20-7-724 JA¡IUARY 5,202t PREPARED FOR: TRIAD PARTNERS,INC. ATTN: NICK WEAVER 1OO1 SOPRIS MOUNTAIN RANCH ROAD BASALT, COLORADO 81621 nweaver@triad Dartners.com TABLE OF'CONTENTS PURPOSE AND SCOPE OF STUDY PROPOSED CONSTRUCTION ... SITE CONDITIONS SUBSIDENCE POTENTIAL FIELD EXPLORATION SUBSURFACE CONDITIONS FOT]NDATION BEARING CONDITIONS DE SIGN RECOMMENDATIONS FOUNDATIONS FOUNDATION AND RETAINING WALLS FLOOR SLABS TJNDERDRAIN SYSTEM SURFACE DRAINAGE................ LIMITATIONS FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS ........- 1 - -2- a -3 -3- -3 - -4- -5- -6- -6- -3- -7 - Kumar & Associates, lnc. @ Project No. 20-7-724 PURPOSE AND SCOPE OF STUDY This report presents the results ofa subsoil study for a proposed residence to be located on LotM-26, Golden Stone, Roaring Fork Mesa, Aspen Glen Subdivision, Garfield County, Colorado. The project site is shown on Figure 1. The purpose 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 Triad Partners, Inc. dated November 24, 2021. A freld 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 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 We assume the proposed residence will be a one or two story structure over crawlspace or basement with attached garage. Ground floor will be structural over crawlspace for the living areas and slab-on-grade for the basement or garage. Grading for the structure is assumed to be relatively minor with cut 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 recommendations contained in this report. SITE CONDITIONS The subject site was vacant at the time of our field exploration. The ground surface is sloping gently down to the north at a grade of around 5%. A dry drainage ditch runs north of the lot boundary. Vegetation consists of grass and weeds with cottonwood trees growing off of the lot in the drainage. Kumar & Associates, lnc. @ Project No. 20-7-724 a-L- SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen development. These rocks are a sequence ofgypsiferous 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 area, several sinkholes were observed scattered throughout the Aspen Glen development mostly east of the Roaring Fork River. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork River Valley. Sinkholes were not observed in the immediafe arca of the subject lot. There is a mapped sinkhole about i,500 feet south of this lot in County Road 109. 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 M-26 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. FIELD BXPLORATION The field exploration for the project was conducted on November 30,2020. 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 1% inch and2 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 retumed to our laboratory for review by the project engineer and testing. Kumar & Associates, lnc. o Project No. 20-7-724 -3- SUBSIIRFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2, The subsoils consist of about 1 foot of topsoil in Boring 1 or 6 feet of fill in Boring 2 overlying interlayered silt and sand, clayey sand and gravel, and sandy clay to depths of l6 and l8 feet underlain by dense, silty sand and gravel with cobbles. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in Boring 2. Laboratory testing performed on samples obtained from the borings included natural moisture content and gradation analyses. Results of swell-consolidation testing performed on relatively undisturbed drive samples, presented on Figures 4 and 5, indicate low compressibility under conditions of loading and wetting. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at the time of drilling and the subsoils were slightly moist to moist. FOUNDATION BEARING CONDITIONS The natural soils, below the topsoil or fill, are adequate for support ofspread footing foundations. The silty sand and gravel subsoils are overlain by interlayered clay, sand and gravel and sand and silt soils. At assumed excavation depths we expect the foundation excavation to expose silt and sand soils or fill soils. Any fill soils in the excavation should be removed from below footing areas and replaced with compacted structural fill or the footings lowered down to the natural soils. There is some risk of differential settlement for footings which transition between soil types or soil and structural fill. DESIGN RECOMMENDATIONS FOLINDATIONS 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 soils. The design and construction criteria presented below should be observed for a spread footing foundation system. l) Footings placed on the undisturbed natural soils or structural fill should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we Kumar & Associates, lnc. o Project No. 20-7-724 -4- 4) expect settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. The footings should have a minimum width of 16 inches for continuous walls and 2 feetfor 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 area. 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 ofthis report. All existing fill, topsoil and any loose disturbed soils should be removed and the footing bearing level extended down to the relatively dense natural granular soils. The exposed soils in footing area should then be moistened and compacted. A representative ofthe geotechnical engineer should observe all footing excavations prior to concrete placement to evaluate bearing conditions. 5) 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, 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 increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain should be provided to prevent hydrostatic pressure buildup behind walls. 2) 3) 6) Kumar & Associates, lnc. @ Project No. 20-7-724 -5- 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 in pavement and walkway areas should be compacted to at leastg5o/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. Relatively well graded granular soils could be used as backfill to help reduce the settlement potential. 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 0.40. 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 a granular material compacted to at least 95%o of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil and fill, are suitable to support lightly loaded slab- on-grade construction. Any fill soils encountered below slab areas should be removed and replaced with compacted structural fill. 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 50Yo retained on the No. 4 sieve and less than 2YopassingtheNo.200 sieve. All fillmaterials for support of floor slabs should be compacted to at least95Yo of maxtmum standard Proctor density at a moisture content near optimum. Required f,rll can consist of the on- site granular soils devoid of vegetation, topsoil and oversized rock. Kumar & Associates, lnc. o Project No. 20-7-724 -6- TINDERDRAIN SYSTEM Although free water was not encountered during our exploration, 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 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 surounded 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 1o/oto a suitable gravity outlet or drywell. Free-draining granular material used in the underdrain system should contain less than 2Yo passingthe 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 l% feet deep. SIIRFACE 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 95Yo of the maximum standard Proctor density in pavement and slab areas and to at least 90%o of the maximum standard Proctor densþ 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 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 capped with about 2 feet of the on-site, finer graded, 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. Kumar & Associates, lnc. o Project No, 20-7-724 -7 - 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 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 conditions may not become evident until excavation is performed. If conditions encountered dnring 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 pu{poses. 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 veriSr 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 ofexcavations and foundation bearing strata and testing ofstructural fill by a representative of the geotechnical engineer. Resp ectfu lly Submitted, Kumar & Associates, lnc. James H. Parsons, E.I. Reviewed by: Daniel E. Hardin, P JHPlkac t ftt( t"r Xumar & Associates, lnc. @ Project No. 20-1-724 3 _- ./- þ0ÞJ found rebor friih plostic--ìcp, PLS No Ji6.1B 6066 Fsund rebo¡ \Yith \ eoer cap, PIS No. 6070 z '*- 2.\oae ?. I -tì ' 6C6/ 7.5' Uiilily srd drol¡oge e.senìenl rs per re.ord p¡ct. itrp:cal o; si,ie arìd reðr lot :¡es) .E68 11.5' Utility ond pedestr-on occess edsemèni for si¿eroìks têr record plct, (llpicol cll fro¡t iol lines) ! le e. ped. Fouid rebor riti p osti. 3J6J3No. 6il7:3 { I f i'/ e \ \ \ \Fcund reocr Ìirh plústc fTø D occa, PLS No, ii6JB Locol benchnror¡: Top Cop = 6072.50 -.---\-<__ 3loq sr bCrrb eol o \ ô'\ 6Llrc Loo" 6073 15 30 APPROXIMATE SCALE-FEET t;^ t I \,\ ài\r,-eN u þt z6 12.96J sq. fi. Parcel No. 2\1ltl0l{)30 :j o BORING \ t'uildirg "ñ1.,p"0er prq| -''4$'ñ\'.* 2 t.\ (\ 20-7 -724 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 3 BORING .I EL. 6070' BORING 2 EL. 6068.5' 0 0 20/ 12 tr 18/ 12 WC=3.3 DD=1 1 2 q so/5 10 20/1 WC= 10 FU L¡J L! IT F- o_tJÕ 2 12/ 12 WC=4.6 -200=38 FU L!L! I-t"-(L L¡lo 4 tf, 13/ 12 WC= 15.4 DD= 1 04 37 /12 WC= 1 8.9 DD= 1 04 15 20 2050/2 25 25 20-7 -724 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND m ffi 1.../l l.¿91 (;:.;Àlzi trz H TOPSOIL: SAND, CLAYEY, cRAVELLY, ORGANICS, FIRM, SLIcHTLY MOIST, RED FILL: SANDY, SILTY, CLAYEY, SCATTERED GRAVEL, MEDIUM DENSE TO DENSE, SLIGHTLY MOIST, RED. SILT (SM-ML): SANDY TO VERY SANDY, SCATTERED GRAVEL, VERY STIFF OR MEDIUM DENSE, SLIGHTLY MOIST, RED. CLAY (CL-SC): SANDY TO VERY SANDY, STIFF, SLIGHTLY MOIST, RED CLAY (cL): SANDY, HARD, MolST, RED SAND AND GRAVEL (SC-GC): CLAYEY, SCATTERED COBBLES, DENSE, SLIGHTLY MOIST, RED-GRAY. SAND AND GRAVEL (SM-GM): COBBLES, SILTY, DENSE, SLIGHTLY MOIST, RED-GRAY DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE. i DRTVE SAMpLE, 1 5/8-tNCH t.D. SpLtT SPOON STANDARD pENETRATTON TEST 1q712 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 38 BLOWS OF A 14O-POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. f enacrrcal AUcER REFUSAL. NOTES THE EXPLORATORY BORINGS WERE DRILLED ON NOVEMBER 30, 2O2O WITH A 4-INCH-DIAMETER CONTINUOUS-FLIGHT POWER AUGER. 2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY TAPING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 5. 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 DENSTTY (pcf) (nSrV OZZ1 0); -2QO= PERCENTAGE PASSING NO. 200 SIEVE (ASTM 01140). 20-7 -724 Kumar & Associates LEGEND AND NOTTS Fig. 5 ¡ SAMPLE OF: Sond qnd Silt FROM:Boringl@^4' WC = 3.3 %, DD = 112 pc'f I lj-l' I ii 1,.-- 1 I I ltii l l I ll :i i: I ! I i i I ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 'l .............. ........... I I:L ! I ñ JJ¡J =tt1 I z.o t- â Jo U)z.oo JJ t¡J =U) I z.otr o Jo v1zoO 2 -3 -4 0 2 -3 APPLIED PRESSURE - KSF I.O APPLIED PRESS 10 100 SAMPLE OF: Sondy Silty Cloy FROM:Boringl@15' WC = 15.4 %, DD = 104 pcf H ft€ Kumor ond koclotð, lnc, Swoll Consolidolion tætìng pedomed ¡¡ occodo.cô with ffi D-4546. l l I t. I ! I ¡ i I I : ! I : l I I NO MOVEMENT UPON WETTING :.- -- ¡ f00 20-7 -724 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4 ã ¡ 9 3 3 SAMPLE OF: Silty Cloy FROM: Boring 2@ 15' WC = 18.9 "Á, DD = 104 pcf full, ü¡thout th. wdtên i I-t--i ! llr1 I i ¡ : NO MOVEMENT UPON WETTING :i :i,t : : i. I l : JJ TJ =ln I z.() Ë o =o(n z.oO 0 2 -3 4 I.O APPLIED PRESSURE - KSF 100 20-7 -724 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5 I rc iiry*fi'ffi'r:ü:fni'ï:';..* -7 TABLE 1 SUMMARY OF LABORATORY TEST RESULTS No.20-7-724 GRÂDÂTIONSAMPLE LOCÀTION SAND (%) PERCENT PASSING NO. 200 stEVÊ to/"\ LIQUID LIMIT PLASIIC INDEX (o/"1 lDsfì UNCONFINED COMPRESSIVE STRENGTH SOIL TYPEBORING tftt DEPTH to/ol NATURAL MOISTURE CONTENT lDctl NATURAL DRY DENSIÏY GRAVEL f/"\ Sand and Silt143.3 112 Clayey Sand and Gravell01.4 Sandy Silty Clay15t5.4 104 38 Very Clayey Sand and Gravel2104.6 Silty Clay1518.9 104