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HomeMy WebLinkAboutSubsoils Report for Foundation DesignKumar & AssoclaNs, Inc. K Geotechnical and Materials Engineers 5020 County Road 154 and Environmental Scientists Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@akumarusa.com An Employee Owned Company 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-20, ASPEN GLEN 382 GOLDEN BEAR DRIVE GARFIELD COUNTY, COLORADO PROJECT NO.21-7-739 DECEMBER 9, 2021 PREPARED FOR: ANDREA SOUSA 110 HARRIS STREET, APT 206 BASALT, COLORADO 81621 and rea Sousa mail.com v TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY........................................................................................ I - PROPOSEDCONSTRUCTION................................................................................................ I SITECONDITIONS...................................................................................................................- 1 SUBSIDENCEPOTENTIAL.....................................................................................................- 2- FIELDEXPLORATION............................................................................................................ 2 SUBSURFACECONDITIONS.................................................................................................. 2- FOUNDATION BEARING CONDITIONS............................................................................... 3- DESIGNRECOMMENDATIONS............................................................................................. 3- FOUNDATIONS.................................................................................................................... - 3- FOUNDATION AND RETAINING WALLS ................................................................... - 4- FLOORSLABS...................................................................................................................... - 5 - UNDERDRAINSYSTEM..................................................................................................... - 6- SURFACEDRAINAGE..................................................................................................... 7- LIMITATIONS............................................................................................................................ 7- 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 Kumar & Associates, Inc. 0 Project No. 21-7-739 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot FW-20, 382 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 Andrea Sousa, dated September 10, 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 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 1. 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 purpose 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. Kumar & Associates, Inc. 0 Project No. 21-7-739 -2- 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 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-20 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 September 15, 2021. Two exploratory borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The borings were advanced with 4-inch diameter continuous flight augers powered by a truck - mounted CME-45B drill rig. The borings were logged by a representative of Kumar & Associates, Inc. Samples of the subsoils were taken with 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 testis 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 % foot of organic topsoil, the subsoils consist of very stiff to hard, slightly sandy clay. At Kumar & Associates, Inc. 0 Project No. 21-7-739 -3- a depth of about 6 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 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 and grain size analyses. Swell -consolidation testing was performed on relatively undisturbed drive samples of the clay subsoils. The swell -consolidation test results, presented on Figures 4, indicate low compressibility under relatively light surcharge loading and a moderate expansion potential when wetted under a constant light surcharge. Undisturbed sampling of the silty sandy gravel soils was not possible due to the rock content. Results of gradation analyses performed on the minus 1 %z-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. 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 3-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 FOUNDATIONS 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 three-foot depth of compacted structural fill. Kumar & Associates, Inc. 0 Project No. 21-7-739 -4- 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 pressurr 500ps2) Based on experience, we expect settlement of footint ne an constructed as discussed in this section will be up to about 1 inch. There could be some additional movement if the bearing soils were to become wet. 3) The footings should have a minimum width of 16 inches for continuous footings and 24 inches for isolated pads. 4) Continuous foundation walls should be heavily 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 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 a earing elevation for frost protection. Placement of foundations at east 36 inch s- elow 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 3 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 1 Meet 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. 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 60 pcf for backfill consisting Kumar & Associates, Inc. 0 Project No. 21-7-739 -5- of the on -site fine-grained soils and at least 50 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% 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 0.50. 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% 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 if the subgrade soils were to become wet. If used, slab -on -grade construction should be placed on the natural coarse granular soils or 3 feet of compacted structural fill consisting of a suitable imported Kumar & Associates, Inc. 0 Project No. 21-7-739 WOE 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 1 %2-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 50% passing the No. 4 sieve and less than 2% 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 at or above optimum moisture content, and compacted to at least 95% 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. However, 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. UNDERDRAIN 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 Kumar & Associates, Inc. 0 Project No. 21-7-739 -7_ 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 1 foot below lowest adjacent finish grade, and sloped at a minimum 1% 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 50% passing the No. 4 sieve and less than 2% passing the No. 200 sieve. The drain gravel should be at least I Meet deep and covered with filter fabric such as Mirafi 140N. Void form below the foundation can act as a conduit for water flow. 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. Drying could increase the expansion potential of the clay soils. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to at least 95% of the maximum standard Proctor density in pavement areas and to at least 90% 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 12 inches in the first 10 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in paved areas. 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 at this time. We make no warranty either express or implied. Kumar & Associates, Inc. 0 Project No. 21-7-739 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 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. 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 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. Respectfully Submitted, Kumar & Associates, Inc. qa"� It pau-r� James H. Parsons, P.E. Reviewed by: Steven L. PaN JHP/kac Kumar & Associates, Inc. ® Project No. 21-7-739 M DRAINAGE & I LANDSCAPE EASEMENT N34-25'52"W 114.80' . r BALD EAGLE WAY S34"25'52"E 114.80' C20 C21 32.fi4 82,16 C22 C23 0 iv an C42 2.f37 S3 '15'17"E `'' S3ZI5'17"E _ r _ r 100.04' _.. 85.31' r ��C41 Tti LLOTok LbT 11% 2- P�_0. s ACt P .285 AC± 0 0.283 ACf -1 0 382 GOLDEN BEAR DR F�`I L _J LOBORING 2 j L r C1 fi ENVELOPE C25 74.57 88.19 (TYP.) C37 0 S,32*1 5'1 7-*E 162.76' 1, 361.54' GOLDEN BEAR DR 100.00 100.00 11.84 C27 --� CP z ff _ zOT �' -- T NOT 8 ? 0.253 rACt }ODa 0.253 ACf c�0.253 ACf 0 --�' 20 0 20 40 APPROXIMATE SCALE -FEET 21-7-739 1 Kumar & Associates I LOCATION OF EXPLORATORY BORINGS I Fig. 1 BORING 1 BORING 2 0 39/12 0 25/12 WC=8.8 WC=1 1.9 DD=1 10 DD=108 -200=91 5 28/12 J 20/12 5_ F w WC=7.8 W I CL a Ui 32/6,50/5 10 50/5 - WC=2.0 10 +4=43 -200=20 15 15 p I P $a ej e� �R 21-7-739 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 yE Si LEGEND] ® TOPSOIL; CLAY AND SILT WITH ORGANICS, FIRM, MOIST, BROWN. CLAY (CL); SLIGHTLY SANDY, CALCAREOUS, STIFF, SLIGHTLY MOIST, BROWN. GRAVEL AND COBBLES (GM); SANDY, SILTY, PROBABLE BOULDERS, DENSE, SLIGHTLY MOIST, ' BROWN, SUBROUNDED ROCK. DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE. I DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST. I 25/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 25 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBER 15, 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 NOT MEASURED AND THE LOGS OF THE 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 RESULTS: WC = WATER CONTENT (%) (ASTM D2216); DD = DRY DENSITY (pcf) (ASTM D2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913); —200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140). 21-7-739 1 Kumar & Associates I LEGEND AND NOTES I Fig. 3 SAMPLE OF: Slightly Sandy Clay -- FROM: Boring 1 ® 2.5' WC = 11.9 %, DD = 108 pcf 3 � EXPANSION UNDER CONSTANT J w PRESSURE UPON WETTING N 2 I Z O 1 — I a 0 J O N Z 0 1 I I —1 —2 ,1 100 1.0 APPLIED PRESSURE - KSF 10 3 2 1 J Li N 0 I Triz o —1 Q 0 J O to z -2 O U —3 Li 1 1.0 APPLIED PRESSURE - KSF 10 100 21-7-739 Kumar & Associates SWELL —CONSOLIDATION TEST RESULTS Fig. 4 SAMPLE OF: Slightly Sandy Clay FROM: Boring 2 ® 5' WC = 7.6 %, DD = 107 pcf EXPANSION UNDER PRESSURE UPON CONSTANT WETTING 1 I Thmnpvl lM rnYlp npp>r Wy to 1ha �Ilell �ISL�C alepfYEYCKd��+pf to fup, rilhwl use Mrl�++ appmwl of I{unwr and RaaocfMaa, Inc- S.eY Canw66alion taltlnq PPNwnw! � oCwbmue rSlh 75fY 6�5{0. HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS :24 HRS 7 HRS IN 4M N 1 IN W U.S. STANDARD SERIES go 01DO ap A 10 a7e CLEAR SQUARE OPENINGS 4' 1 1 3' 'e 1 0 100 90 10 20 eD — 70 I 1 30 40 so p —I 50 so i7 60 30 70 e0 20 10 90 0 100 .001 ,aOR .o0s .00G .012 .037 .073 .150 .boa .800 t.te 24594.76 P.S 1P 3i.1 7a,2 152 DIAMETER OF PARTICLES IN MILLIMETERS CLAY TO SILT SAND GRAVEL COBBLES FINE MEDIUM 1COARSE1 FINE I COARSE GRAVEL 43 % SAND 37 % SILT AND CLAY 20 % LIQUID LIMIT — PLASTICITY INDEX — SAMPLE OF: Stilly Sandy Gravel FROM: Boring 2 O 10' These lout resUlta apply only to fhe samples which wan loafed. The lraifng nporF shall not 6e rappeduced, except in full, wllhovl the wrlTlen apprava} of Kumar & Asscolotss, Inc. Stsrs onclyals lnsfln8 to performed In aocordo nce wlih AS06913. ASTM D7926, ASTM C136 and/or ASTM D1140. S 21-7-739 Kumar &Associates GRADATION TEST RESULTS Fig. 5 � � k k a- M U U U § 2 2 2 9 7 A 2 Lu 0 LU LU ' z§& =u H \ )= m L § § � @ Or 0 u j§\ 2 c G (L<m z w z £ k 9 -1 ° § 0 k&k 3 0 � e�z ? — _ z� — _jk§ _ §dz 00 06 0 q — z�u § a.® 3 LU w M k cn