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Home My WebLink AboutSubsoils Report for Foundation DesignI T rt Hffi,*,{lTflttrf itvi *"' fn Apltcys* firncd CompEny 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@Jcumarusa.com www.kumarusa,com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT FW-19, ASPEN GLEN TBD GOLDEN BEAR DRIVE GARFTELD COUNTY, COLORADO PROJECT NO.23-7-260 MAY 26,2023 PREPARED FOR: YOLO FLORIDA LTD ATTN: RAY AND JUDY KELLY 174 WATERCOLOR WAY, PMB 355 SANTA ROSA BEACH, FL23459 rimeL1@aol.com TABLE OF CONTENTS PROPOSED CONSTRUCTION SITE CONDITIONS......... SUBSIDENCE POTENTIAL FIELD EXPLORATION SIJB SURFACE CONDITIONS FOLINDATION BEARING CONDITIONS DESIGN RECOMMENDATIONS FOUNDATIONS FOUNDATION AND RETAINING WALLS FLOOR SLABS LINDERDRAIN SYSTEM SURFACE DRAINAGE LIMITATIONS......... FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOGS OF EXPLORATORY BORINGS FIGURE 3 - LEGEND AND NOTES FIGIJRE 4 - SWELL-CONSOLIDATION TEST RESULTS FIGURE 5 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS I 1 ..-1- a .| J 3- 3- 6- -4- -5- -6- -6- Kumar & Associates, lnc. @ Project No. 23-7-260 PURPOSE AND SCOPE OF STUDY This report presents the results ofa subsoil study for a proposed residence to be located on Lot FW-19, TBD Golden Bear Drive, Aspen Glen, 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 YOLO Florida Ltd., dated Aptil12,2023. 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 werc 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, recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION At the time of our study, design plans for the residence had not been developed. The building is proposed in the area roughly between the exploratory borings shown on Figure l. The building will likely be a one- or two-story wood-frame structure with attached garage possibly over a basement level. We assume excavation for the building will have a maximum cut depth of one level, up to about 8 feet below the existing ground surface. For the pu{pose of our analysis, foundation loadings for the structure were assumed to be relatively light and 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 relatively flat. Vegetation consists of grass and weeds. A drainage ditch is near the northeast edge of the subject site. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen Subdivision. 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 Kumar & Associates, lnc. @ Project No. 23-7-260 a'L- 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 lower Roaring Fork Valley. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork 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 FW-19 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 EXPLORATION The field exploration for the project was conducted on April 28, 2023. 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-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 saniples 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 Yzfootof organic topsoil, the subsoils consist of stiff to very stiff, sandy clay. At a depth of about 4% feet in Boring 1 and 9 feet in Boring 2, the subsoils became a dense, silty sandy gravel and cobble mixture. The soils encountered in the borings are similar to the soils encountered at other nearby lots. The clay portions ofthese soils can possess an expansion potential when wetted. Laboratory testing performed on samples obtained during the field exploration included natural moisture content and density and grain size analyses. Swell-consolidation testing was performed on a relatively undisturbed drive sample of the clay subsoils. The swell-consolidation test results, presented on Figure 4, indicate low to moderate compressibility under relatively light to Kumar & Associates, lnc. @ Project No. 23-7-260 -3- moderate surcharge loading. Undisturbed sampling of the silty sandy gravel soils was not possible due to the rock content. Results of gradation analyses performed on the minus lVz-inch fraction of the gravel subsoils are presented on Figure 5. The laboratory testing is summarized in Table 1. No free water was encountered in the borings at time of drilling and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The upper clay soils encountered at the site possess moderate expansion potential when wetted and loaded. The underlying gravel soils possess moderate bearing capacity and typically low settlement potential. Foundations placed on the upper clay soils will have a risk of foundation movement, especially if the bearing soils become wetted, possibly resulting in distress to the proposed residence. Surface runoff, landscape irrigation, and utility leakage are possible sources of water which could cause wetting. A full-depth basement level would remove most of the clay soils from below footing and slab areas and allow the foundation to bear entirely on the gravel soils reducing the risk of foundation and slab movement. We recommend the upper clay soils be removed from below the building area and the foundation bear entirely on the underlying gravel soils or on a minimum 2-foot depth of compacted structural fill (such as in the garage area). Structural fill should consist of an imported gravel material such as CDOT Class 6 road base. 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 with spread footings placed on undisturbed natural granular soils or a minimum two-foot depth of 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 natural granular soils or compacted structural fill can be designed for an allowable bearing pressure of 2,500 psf. 2) Based on experience, we expect settlement of footings designed and constructed as discussed in this section will be up to about I inch. There could be some additional movement if the bearing soils were to become wet. 3) The footings should have a minimum width of l6 inches for continuous footings and 24 inches for isolated pads. 4) 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 14 feet. Foundation walls acting as retaining structures should also be designed to resist a Kumar & Associates, lnc. @ Project No. 23-7-260 -4- lateral earth pressure as discussed in the "Foundation and Retaining Walls" section of this report. 5) 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. 6) Prior to the footing construction, topsoil and loose disturbed soils should be removed and the foundation excavation extended down to the underlying granular soil or sub- excavated 2 feet below the proposed foundation bearing level for structural fill. The sub-excavated depth should be backfilled to design grade with compacted structural fill. Structural fill should consist of a suitable imported granular material such as CDOT Class 6 base course, moisture conditioned to near optimum moisture content and compacted to 98 percent of maximum standard Proctor density. The fill should extend to at least lt/z feet beyond footing edges. 7) A representative of the geotechnical engineer should observe all footing excavations and test structural fill compaction prior to concrete placement to evaluate bearing conditions. FOI.INDATION 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 50 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 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 slightly above optimum. Backfill placed in pavement 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 Kumar & Associates, lnc. @ Project No. 23-7-260 5 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 0.50. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 375 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 non-expansive material compacted to at least 95%o of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural clay soils possess an expansion potential and slab heave could occur ifthe subgrade soils were to become wet. If used, slab-on-grade construction should be placed on the natural coarse granular soils or 2 feet of compacted structural fill consisting of a suitable imported granular material (CDOT Class 6 Base Course) and precautions should be taken to limit potential wetting of the underlying clay soils. These recommendations will not prevent all slab heave if the clay soils become wetted and the owner should be informed of possible movement and distress. 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 underlain by clay soils 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 I %-inches of vertical movement are recommended. Floor slab control joints should be used to reduce damage due to shrinkage 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 50oh passing the No. 4 sieve and less than2o/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 can consist of a suitable imported granular material, excluding topsoil and oversized rocks. The fill should be spread in thin horizontal lifts, adjusted to within 2o/o of Kumar & Associates, lnc. @ Project No. 23-7-260 -6- optimum moisture content, and compacted to at least 95Yo of the maximum standard Proctor density. All vegetation, topsoil and loose or disturbed soil should be removed prior to fill placement. TINDERDRAIN 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 lYo grade to a suitable gravity outlet, drywell into the gravel soils or sump and pump. 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 Ilz feet deep and covered with filter fabric such as Mirafi 140N. SURFACE DRAINAGE Providing and maintaining proper surface drainage will be critical to the long term, satisfactory performance of the proposed residence. 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. 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 areas and to at least 90%o of the maximum standard Proctor density in landscape areas. Free-draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site, finer graded, 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 6 inches in the first 1 0 feet in unpaved areas and a minimum slope of 2Yz inches in the first 10 feet in paved areas. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 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. Kumar & Associates, lnc. o Project No. 23-7-260 -7 - The canelusicns and recofirmsndations submitted in this report are based upcn the data *btained frcm the exploratary borings drilled at the l*cations indicated an Figure 1, th* prcposed type of construction and cur experience in the area. Sur services do not inelude determining the presence, prevention or possibility of mold cr other biological ecntaminants {MOBC) devcloping in the future. If ths elient is coneerned about MOBC, then a professional in this special field of practice should be e*nsulted. Our findings inelude interpolation and extrapolation of the subsurfacs conditions ielsntified at the exploratory b*rings and variations in the subsurfbce eonditions may not becorns evident until excavati*n is perfcrmed. If conditions encountered during oonstruetian appear to be different ftom those deseribed in this repcrt, we should be notified at once so re-evaluation of the recommendations may be made. This repcrt has been prepared f*r the exclusive use by our client for design plrrposes. We are not responsible far techni*al inteipretati*ns by others of our infonnation. As the prCIject evolves, we should provide eontin*ed eansultati*n and field serviees during construction to review and monitor the implomentation of our re*cmmendaticns, and t$ v*ri$ that the recommendations have been appropriately interpreted. $ignificant design cheng*s may require additional analysis ar rnaditicatic*s of the re*ommendatians presented herein. W* reecmmend on-site obsorvation cf excavations and foundation bearing strata artd testing of struetural fill by a repr*sentative of the geot**hnical engineer. Respectfully Submitteel, Kwraa*rn" & Ass*c$ea{es, Robert L. Duran, F Review*d by: Daniei E. Flardin, F.E. Rl-D/kac Cc: Hngel & Voelkcrs - Keith tuIeDougal {lq:llrrygfuragal{&pn}Wly**3&emS*m) Kumar & Ass*ciates, lrt*. *Pr*jeet ?**. !*"?"flS* 0 50 1 APPROXIMATE SCALE-FEET 23-7 -260 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 3 s n s BORING 1 BORING 2 o 0 27 /12WC=9.8 DD=95 24/12 FLdLJLL I-F(L UJo 5 8/12 WC=9.1 -2OO=74 LL=29 Pl=13 5so/5 FulLJLL IIF(L UJo 10 1050/4 so/ 4 WC=1.6 *4=55 -200=1 0 15 15 23-7-260 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 LEGEND TOPSOIL; CLAY AN SILT, SANDY, FIRM, MOIST, DARK BROWN, ORGANIC. CLAY BROW ( N CL); SANDY TO VERY SANDY, SILTY, STIFF TO VERY STIFF, SLIGHTLY MOIST, GRAVEL AND COBBLES (GM); SILTY, SANDY, WITH BOULDERS, DENSE, SLIGHTLY Mo|ST, MIXED BROWN. DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE. I DRTVE SAMPLE, 1 3/8-tNCH l.D. SPLIT SPOON STANDARD PENETRATION TEST. ^1 t.^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 27 BLOWS OF A 140-P0UND HAMMERz'/ ta FALLTNG 30 TNCHES WERE REeUTRED To DRrvE THE SAMPLER 12 lNcHES. i PRACTICAL AUGER REFUSAL WHERE SHOWN ABOVE BOTTOM OF BORING, INDICATES THAT MULTIPLE ATTEMPTS WHERE MADE TO ADVANCE THE HOLE. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 28, 2023 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 NOT MEASURED AND THE LOGS OFTHE 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 RESULTSI WC = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (PCt) (ISTU D2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTV OOSIS); -20O = PERCENTAGE PASSING No. 200 SIEVE (ASTM Dl 1 a0); LL = LIQUID LIMIT (ASTM DA318);PI = PLASTICITY INDEX (ASTM D4318). 23-7 -260 Kumar & Associates LEGEND AND NOTES Fig. 3 g & 3 d ts cpg J SAMPLE OF: Sondy Silty Cloy FROM:Boringl@2.5' WC = 9.8 %, DD = 95 pcf NO MOVEMENT UPON WETTING { (\ \ \ \ () Th i..t lnc. SxlllCon&lidotion taUn! tsrfomd lnodrdoncc uith A5Tll D-43f6. 1 N JJLJ =]n I zotr 6:otnzoo 0 -1 2 3 -4 -5 r,0 APPLIED PRESSURE - KSF IO 100 Fis. 423-7 -260 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS SIEVE ANALYSISHYDROMETER ANALYSIS NXE RUDIXGS 2,+ HRS 7 HRS U-S. STAf,DARD SERIES --- --t---""--j-------t-----"-i-- "-f------- -- -* .-l - ' -- -' -'t ""r----" -1-t' -t-l i I --l---{ - rr'-------t---r---l-------l----l*-' ----l-'---{-, i t-<-r-i-" ' : : : : : : : : : : : : : : : : : : : l::: -{ -----t----- - I E F too 90 ao 70 80 30 0 50 20 lo o o to 20 50 N 50 60 70 80 90 roo I E ap E ,123 2.ORTICLES IN MILLIMETERS IOF PA CLAY TO SILT COBBLES GRAVEL 55 X SAND LIQUID LIMIT SAMPLE OF: Sllghtly Sllty Sondy Grovel 55% PLASTICITY INDEX SILT AND CLAY 1A % FROM:Borlng2l'lO' Th.ta l.rl rotulb opply only lo lh. Bqmplcr whlch Y.ro l!81.d. Th!hsllng nporl lhqll nol b. roprcduc.d,.xccpl ln full, wllhoul lhr yrltl.n opprcvql of Xumqr & Arroslolcr, lnc.Slry. onolyrls t!.tlng lr p.rlom.d lnoccordonc! vlth ASTI, D6913' ASTM D7928, ASTM ClS6 ond/or ASTI, Dlti|o. SAND GRAVEL FINE MEDIUM COARSE FINE COARSE Fis. 5Kumar & Associates GRADATION TEST RESULTS23-7 -260 l(+A fliffififftrffi*g,g'i** TABLE 1 SUMMARY OF LABORATORY TEST RESULTS SOIL TYPE Sandy Silty Clay Very Sandy Silty Clay Slightly Silty Sandy Gravel {osfl UNCONFINED COMPRESSIVE STRENGTH J1 t%l PLASTIC INDEX ATTERBERG LIMITS LIQUID LIMIT (o/"1 29 PERCENT PASSING NO. 2()() SIEVE 74 0135 SAND P/"1 GRADATION P/,1 GRAVEL 55 9s NATURAL DRY DENSITY {ocfllol NATURAL MOISTURE CONTENT 9.8 19 t.6 )1/" 5 0I tft) DEPTH SAMPLE LOCATION BORING I 2 No.23-7-260