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HomeMy WebLinkAboutSoils Report 07.08.2020ICFA Kumar & Associates, Inc. Geotechnical and Materials Engineers and Environmental Scientists 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.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 WARD RESIDENCE LOT SD -24, ASPEN GLEN SUNDANCE TRAIL GARFIELD COUNTY, COLORADO PROJECT NO. 20-7-336 JULY 8, 2020 PREPARED FOR: RESORT CONCEPTS ATTN: RICK HERMES P. O. BOX 5127 EDWARDS, COLORADO 81632 (rickh(i resortconcentsco.com) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 1 - SUBSIDENCE POTENTIAL - 1 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 2 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS -- 3 - FLOOR SLABS - 4 - UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 5 - LIMITATIONS - 5 - 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 FIGURE 6 - GRADATION TEST RESULTS TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, Inc. Project No. 20-7-336 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for the proposed Ward residence to be located on Lot SD -24, Aspen Glen, Sundance Trail, 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 Resort Concepts dated June 10, 2020. 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, design recommendations and other geotechnical engineering considerations based on the proposed construction and the subsurface conditions encountered. PROPOSED CONSTRUCTION The residence will be a single story wood frame structure with an attached garage located on the lot as shown on Figure 1. Ground floors will be slab -on -grade at a finish elevation slightly above the existing ground surface. Grading for the structure is expected to be relatively minor with cut depths between about 2 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 lot was vacant at the time of the field exploration and it appeared the ground surface had undergone some minor overlot grading. The terrain is a very low broad mound that slopes down gently to the northeast and southwest. There is an estimated 1 to 2 feet of elevation difference across the proposed building foot -print. A pond is located adjacent the northeast side of the lot. Vegetation consisted of grass and weeds. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen development. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and Kumar & Associates, Inc. Project No. 20-7-336 -2- 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 development, mostly east of the Roaring Fork River. These sinkholes appear similar to others associated with the Eagle Valley Evaporite in other areas of the Roaring Fork River Valley. Sinkholes were not observed in the immediate area of the subject lot. The closest known sinkhole is located a few hundred feet northwest of Lot SD -24. 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 SD -24 throughout the service life of the proposed residence, in our opinion, is low and similar to other platted lots in Aspen Glen; 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 June 12, 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. Samples of the subsoils were taken with 1% inch and 2 inch I.D. spoon samplers. The samplers were driven into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This test is similar to the standard penetration test described by ASTM Method D-1586. The penetration resistance values are an indication of the relative density or consistency of the subsoils. Depths at which the samples were taken and the penetration resistance values are shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The subsoils, encountered below about''/ foot of topsoil, consisted of 11/2 to 5'/2 feet of stiff, sandy silty clay underlain by relatively dense, silty sandy gravel and cobbles with small boulders down to the maximum drilled depth of 11 feet. Drilling in the dense, coarse granular soils with auger Kumar & Associates, Inc. Project No. 20-7-336 --3- equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in the deposit in both borings. 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 silty clay soils, presented on Figures 4 and 5, indicate low to moderate compressibility under conditions of loading and wetting. One sample (Boring 1 at 2.5') showed a low collapse and the other sample (Boring 1 at 5') showed a moderate swell potential when the samples were wetted under a constant 1,000 psf surcharge loading. Results of a gradation analyses performed on a small diameter drive sample (minus 11/2 -inch fraction) of the coarse granular subsoils are shown on Figure 6. The laboratory testing is summarized in Table 1. No groundwater was encountered in the borings at the time of drilling and the subsoils were slightly moist. DESIGN RECOMMENDATIONS FOUNDATIONS 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 coarse granular soils and/or properly placed and compacted structural fill placed on the coarse granular soils. The structural fill can consist of the on-site coarse granular soils (minus 6 -inch fraction) or imported CDOT Class 2, 5 or 6 aggregate base course. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Footings placed on the undisturbed natural coarse granular soils and/or compacted structural fill should be designed for an allowable bearing pressure of 2,500 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 a minimum width of 18 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 area. 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 (if any) should also be designed to Kumar & Associates, Inc. Project No. 20-7-336 -4 - resist a lateral earth pressure corresponding to an equivalent fluid unit weight of at least 50 pcf. 5) The topsoil, all sandy silty clay and any loose disturbed soils should be removed and the footing bearing level extended down to the relatively dense coarse granular soils. The exposed soils should then be moistened and compacted. The structural fill below footing areas should extend beyond the edge of the footings a distance equal to at least 1/2 the depth of fill below the footings and be compacted to at least 98% standard Proctor density at a moisture content within about 2% of optimum. 6) A representative of the geotechnical engineer should observe all footing excavations and test structural fill compaction on a regular basis prior to concrete placement to evaluate bearing conditions. FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade construction. There could be some slab movement (settlement or heave) in areas underlain by the silty clay soils, primarily if the subgrade were to become wetted. Removing the silty clay soils and replacing with compacted structural fill below the floor slabs would act to reduce the risk of floor slab movement. We should review the slab subgrade conditions at the time of construction with respect to the need for structural fill below floor slab areas. Providing a structurally supported floor over crawlspace, commonly used in the area, would have a low risk of floor movement. 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 6 inch layer of sand and gravel aggregate base course should be placed immediately beneath floor slabs -at -grade for support and to facilitate drainage. This material should consist of minus 2 -inch aggregate with at least 50% retained on the No. 4 sieve and less than 12% passing the No. 200 sieve. All fill materials for support of floor slabs should be compacted to at least 95% of maximum standard Proctor density at a moisture content near optimum. Required fill can consist of the on- site coarse granular soils, excluding oversized (plus 6 -inch) rocks, or CDOT Class 5 or 6 aggregate base course. We recommend vapor retarders conform to at least the minimum requirements of ASTM E1745 Class C material. Certain floor types are more sensitive to water vapor transmission than others. Kumar & Associates, Inc. Project No. 20-7-336 -5 - 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 E1745 Class A material. The vapor retarder should be installed in accordance with the manufacturers' recommendations and ASTM E1643. UNDERDRAIN SYSTEM It is our understanding the proposed finished floor elevation at the lowest level is at or above the surrounding grade. Therefore, a perimeter foundation drain system is not required. 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 also create a perched condition. We recommend below -grade construction, such as retaining walls and basement areas, be protected from wetting and hydrostatic pressure buildup by an underdrain and wall drain system. If the finished floor elevation of the proposed structure is revised to have a floor level below the surrounding grade, we should be contacted to provide recommendations for an underdrain system. Any earth retaining structures should be properly drained. SURFACE DRAINAGE The following drainage precautions should be observed during construction and maintained at all times after the residence has been completed: 1) Inundation 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 95% of the maximum standard Proctor density in pavement and slab areas and to at least 90% of the maximum standard Proctor density 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. 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. The conclusions and recommendations submitted in this report are based upon the data obtained Kumar & Associates, Inc. Project No. 20.7.336 -6 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 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 recommendations, and to verify 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 of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer. Respectfully Submitted, Kumar & Associate Inc. 4 David A. Young, P.E Reviewed by: �... � Com. ---u.. Steven L. Pawlak, P.E. DAY/kac cc: Resort Concepts — Jeff Townsend (hownsu,; ,.(r Ha:+rtconceptsc o.com) Eggers Architecture — Don Eggers (done ci ,!,: Ly gersarchitecture.com) Kumar & Associates, Inc. Project No. 20-7-336 7 • GARAGE BORING 2 PROPOSED RESIDENCE BORING: EXISTING POND LOT SD -24 LOT SD -7 15 0 15 30 APPROXIMATE SCALE -FEET 20-7-336 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 0 5 10 L- BORING 1 EL. 100' 17/12 WC=1 0.9 DD=91 -200=90 46/12 WC=10.2 DD=107 40/6, 50/4 BORING 2 EL. 99.5' 53/6 55/6 WC=2.0 +4=40 -200=16 0 5 10 -- 15 15 20-7-336 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 5—CP to 63•C.g 3 1 p LEGEND I TOPSOIL; SANDY SILT AND CLAY, FIRM, SLIGHTLY MOIST, BROWN, ROOT ZONE. / h CLAY (CL); SILTY, SLIGHTLY SANDY, STIFF, SLIGHTLY MOIST, BROWN, CALCAREOUS. GRAVEL AND COBBLES (GM); WITH SMALL BOULDERS, SANDY, SILTY, DENSE, SLIGHTLY MOIST, BROWN, ROUNDED TO SUB—ROUNDED ROCKS. DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE. DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST. 17/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 17 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. f PRACTICAL AUGER DRILLING REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 12, 2020 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 MEASURED BY HAND LEVEL AND REFER TO GROUND SURFACE AT BORING 1 AS BENCHNMARK WITH AN ASSUMED ELEVATION OF 100'. 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. FLUCTUATIONS IN GROUNDWATER LEVEL MAY OCCUR WITH TIME. 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). 20-7-336 Kumar & Associates LEGENDS AND NOTES Fig. 3 2 0 .. —2 —4 w N SAMPLE OF: Slightly Sandy Silty Clay FROM: Boring 1 @ 2.5' WC = 10.9 %, DD = 91 pcf —200 = 90 —12 Mete !qt rcI'.D. apply etch. to the aemplee hated. The teedeep roper! Ila not be reproduced, e.eept m lam...Shout 11. edllen opl.n d eQ 1{urmor and hsoc.olee, Mc. S.el. Cpneef4Qellon trebno performed .n oxe,denee iRh ASAI D-4546 ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING 1.0 APPLIED PRESSURE - KSF 10 100 20-7-336 Kumar & Associates SWELL—CONSOLIDATION TEST RESULTS Fig. 4 CONSOLIDATION - SWELL 2 1 0 —1 —2 SAMPLE OF: Slightly Sandy Silty Clay FROM: Boring 1 © 5' WC = 10.2 %, DD = 107 pcf I. -three test mel• apply only to the 'samples I.Hsd• The tee(l q report. shall not ha ,spraduee4 assay! in fun.'1..4hao} the .nhlSsn approval of Kumar and Associates. Inc Swell C.molI 5! en bleI5n 4Marmed to accordants with nal D-4544 EXPANSION UNDER CONSTANT PRESSURE UPON WETTING 1.0 APPLIED PRESSURE - KSF 10 100 20-7-336 Kumar & Associates SWELL—CONSOLIDATION TEST RESULTS Fig. 5 HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS U.S. STANDARD SERIES 24 HRS 7 HRS 100 45 MJN 15 MIN 601.4IN 191.1IN 4MIN 1MIN #200 /100 #50 #40 ♦-30 #18 #1P a�8 NA 90 80 70 60 50 40 30 20 CLEAR SQUARE OPENINGS 3/8" 3/4" 1 2" 3" 5`e" 0 10 20 30 40 50 60 °- 70 70 80 90 1 I. I I 1 1 1 1.1 11 I 1 I 1 1 I I I • ..t I ..1 III LI I 1 1 1 1111 100 092•!):,T .009 .014 .537 .076 .150 .300 .600 1.18 2.36 8.75 8.5 19 38.1 76.2 177 200 .425 9.0 .... DIAMETER OF PARTICLES fN MILLIMETERS CLAY TO SILT HFINE MEDIUM 'COARSE SAND GRAVEL FINE I COARSE COBBLES GRAVEL 40 % SAND 44 LIQUID LIMIT PLASTICITY INDEX SAMPLE OF: Silty Sand and Gravel SILT AND CLAY 16 FROM: Boring 2 ® 5' These test results apply only to the samples which wore tested. The holing report shall not be reproduced, tempt In full. without the wrlHen approval of Kumar Sc Associates, Inc. Slave analysis testing is perlonned In accordance with ASTM D6913, ASTM D7928, ASTM C136 and/or ASTM D1140. 20-7-336 Kumar & Associates GRADATION TEST RESULTS Fig. 6 K+A Kumar & Associates, Inc.® Geotechnical and Materials Engineers and Environmental Scientists TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 20-7-336 SAMPLE LOCATION NATURAL MOISTURE CONTENT (%) NATURAL DRY DENSITYPASSING (pcf) GRADATION PERCENT NO. 200 SIEVE ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (psfl SOIL TYPE BORING DEPTH (ft) GRAVEL (%) SAND (%) LIQUID LIMIT (%) PLASTIC INDEX (%) 1 21/2 10.9 91 90 Slightly Sandy Silty Clay 5 10.2 107 Slightly Sandy Silty Clay 2 5 2.0 40 44 16 Silty Sand and Gravel