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Soils Report 05.05.2020
It -A 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 RESIDENCE LOT 93, IRONBRIDGE 342 RIVERBEND WAY GARFIELD COUNTY, COLORADO PROJECT NO. 20-7-235 MAY 5, 2020 PREPARED FOR: RED DEER REALTY ATTN: LEO CARMICHAEL 766 RIVER BEND WAY GLENWOOD SPRINGS, COLORADO 81601 (1c945 @sopris.net) TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - BACKGROUND INFORMATION - 1 - PROPOSED CONSTRUCTION - 1 - SITE CONDITIONS - 2 - SUBSIDENCE POTENTIAL - 2 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 3 - FOUNDATION BEARING CONDITIONS - 3 - DESIGN RECOMMENDATIONS - 4 - FOUNDATIONS - 4 - FOUNDATION AND RETAINING WALLS - 5 - FLOOR SLABS - 6 - UNDERDRAIN SYSTEM - 6 - SURFACE DRAINAGE - 7 - LIMITATIONS - 7 - FIGURE 1 - LOCATION OF EXPLORATORY BORINGS FIGURE 2 - LOG OF EXPLORATORY BORING FIGURE 3 - LEGEND AND NOTES FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS FIGURE 5 - GRADATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, Inc. ° Project No. 20-7-235 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 93, Ironbridge, 342 River Bend Way, 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 Red Deer Reality dated April 22, 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. BACKGROUND INFORMATION Hepworth-Pawlak Geotechnical (now Kumar & Associates) previously performed a preliminary geotechnical study in the subdivision which included the subject lot, report dated December 31, 2002, Job No. 101 196-1. Information from this report has been reviewed and considered in the preparation of this report. PROPOSED CONSTRUCTION The proposed residence will be a one story structure over crawlspace with a slab -on -grade garage located as shown on Figure 1. Cut depths are assumed to be between 2 to 4 feet and foundation loadings are assumed to be light. If building location, grading or loading information changes, we should be notified to re-evaluate the recommendations presented in this report. Kumar & Associates, Inc. ° Project No. 20-7-235 -2 - SITE CONDITIONS The lot was vacant and the ground surface appeared mostly natural at the time of our field exploration although there were scattered cobbles indicating possible past grading. The terrain is slightly sloping down to the east at a grade of about 4 to 5% in the building area, then steepens to the north and east down to the Roaring Fork River. Elevation difference across the building areas is about 2 feet. Vegetation consists of scattered sage brush, grass and weeds. SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge 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 areas of localized subsidence. During previous work in the area, several sinkholes were observed scattered throughout the Ironbridge Subdivision. 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. 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 93, throughout the service life of the proposed structure, in our opinion, is low and similar to other platted lots in the area; 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 24, 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. Kumar & Associates, Inc. ° Project No. 20-7-235 -3 - Samples of the subsoils were taken with a 1% inch I.D. spoon sampler and a 2 inch I.D. California liner sampler. 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 for testing. SUBSURFACE CONDITIONS Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. In Boring 1 the subsoils consist of about 11/2 feet of topsoil overlying 2'/2 feet of stiff to very stiff sandy clay and silt, further overlying very dense, poorly graded, rounded gravel and cobbles with the silt and sand. In Boring 2, the subsoils consist of about 1'/2 feet of topsoil overlying 41/2 feet of medium stiff sandy clay and silt, further overlying very dense, poorly graded, rounded gravel and cobbles with silt and sand. Drilling in the dense granular soils with auger equipment was difficult due to the cobbles and probable boulders and drilling refusal was encountered in the deposit. 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 a relatively undisturbed drive sample of the upper fine-grained soils from each boring, presented on Figure 4, indicate low to moderate compressibility under loading with a low collapse potential in the sample from Boring 1 when wetted. Results of gradation analyses performed on a small diameter drive sample (minus 1'/2 -inch fraction) of the coarse granular subsoils from Boring 1 are shown on Figure 5. 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. FOUNDATION BEARING CONDITIONS The fine-grained clay and silt soils possess low bearing capacity and low to moderate settlement potential. The underlying coarse granular, sandy gravel and cobble soils possess moderate bearing capacity and relatively low settlement potential. Kumar & Associates, Inc. ° Project No. 20-7-235 -4 - At assumed excavation depths, the subgrade could transition the clay and silt soils and coarse granular soils. Spread footings bearing entirely on the coarse granular soils are preferred for foundation support of the residence to limit settlement potential. Alternately, lightly loaded spread footings can be placed on the upper fine-grained soils with a risk of settlement. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory borings and the nature of the proposed construction, the building be founded with spread footings bearing on the natural granular soils, compacted structural fill or the natural clay and silt soils. 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 should be designed for an allowable bearing pressure of 2,500 psf. Footings placed on the upper clay and silt soils should be designed for an allowable bearing pressure of 1,500 psf. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. Footings placed on the upper clay and silt soils could undergo another 1/2 to 1 inch of settlement if the soils become wetted. 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 should also be designed to resist lateral earth pressures as discussed in the "Foundation and Retaining Walls" section of this report. Kumar & Associates, Inc. ° Project No. 20-7-235 -5- 5) Any existing fill, topsoil, clay and silt soils and loose or 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. Structural fill placed to reestablish design bearing level should consist of a relatively well graded granular soil such as road base compacted to at least 98% of standard Proctor density at near optimum moisture content. The structural fill should extend at least one foot beyond footing edges. 6) A representative of the geotechnical engineer should observe all footing excavations 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 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. Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum standard Proctor density at a moisture content at or slightly above optimum. Backfill placed in pavement and walkway 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 Kumar & Associates, Inc. ° Project No. 20-7-235 -6 - could result in distress to facilities constructed on the backfill. Backfill should not contain organics, debris or rock larger than about 6 inches. The lateral resistance of foundation or retaining wall footings will be a combination of the sliding resistance of the footing on the foundation materials and passive earth pressure against the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated based on a coefficient of friction of 0.45. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 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 compacted to at least 95% of the maximum standard Proctor density at a moisture content near optimum. FLOOR SLABS The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade construction. 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 relatively well graded sand and gravel such as road base should be placed beneath slabs for support. 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 soils devoid of vegetation, topsoil and oversized rock. UNDERDRAIN SYSTEM It is our understanding the proposed finished floor elevation at the lowest level is at or above the surrounding grade and the crawlspace will be relatively shallow, around 3 feet deep. Therefore, a foundation drain system is not required. It has been our experience in the area that local Kumar & Associates, Inc. ° Project No. 20-7-235 -7 - 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 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. All 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 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. 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 Kumar & Associates, Inc. ° Project No. 20-7-235 -8 - 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 & Associates, Inc. Steven L. Pawl Reviewed by: Daniel E. Hardin, .E. SLP/kac Kumar & Associates, Inc. Project No. 20-7-235 LOT 92 VACANT -- \ \-- \ ---- 1‘,0 s\ ---- �s sso \,-- \ \ \ 7 \ 77 i \\ 7 15 0 15 30 APPROXIMATE SCALE -FEET LOT 94 UNDER CONSTRUCTION LOT 93 20-7-235 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1 Lot 93\Drafting \207235-02 DEPTH -FEET 0 5 10 BORING 1 EL. 5948' • 12/12 WC=3.8 DD=106 26/6, 50/4 WC=2.2 +4=51 -200=11 1 66/12 BORING 2 EL. 5950' • 26/12 WC=7.1 / DD=113 /1 11/12 WC=5.3 DD=100 -200=52 1 50/1 0 5 10 15 15 DEPTH -FEET 20-7-235 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2 93\ Drafting \207235-02 LEGEND TOPSOIL; SILTY CLAY, ORGANIC MATTER, MOIST, BROWN. CLAY AND SILT (CL—ML); SLIGHTLY SANDY TO VERY SANDY, STIFF TO VERY STIFF, SLIGHTLY MOIST, BROWN. GRAVEL (GP—GM); SLIGHTLY SILTY, SANDY, POORLY GRADED WITH COBBLES AND BOULDERS, VERY DENSE, SLIGHTLY MOIST, BROWN TO GRAY. ROUNDED GRAVEL COBBLES AND BOULDERS. DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE. DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST. 26/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 26 BLOWS OF A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. t PRACTICAL AUGER REFUSAL. NOTES 1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 24, 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 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 DENSITY (pcf) (ASTM D2216); +4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913); —200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140). 20-7-235 Kumar & Associates LEGEND AND NOTES Fig. 3 CONSOLIDATION SWELL CONSOLIDATION - SWELL 0 — 2 — 3 — 4 — 5 0 — 2 — 3 — 4 10 APPLIED PRESSURE - KSF 10 100 SAMPLE OF: Sandy Silt and Clay FROM: Boring 2 © 2.5' WC = 7.1 %, DD = 113 pcf SAMPLE OF: Sandy Silt and Clay FROM: Boring 1 CSD 2.5' WC = 3.8 %, DD = 106 pcf NO MOVEMENT UPON WETTING ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING These test results apply only to the samples tested. The testing report shall not be reproduced, except in full, without the written approval of Kumar and Associates, Inc. Swell Consolidation testing performed in accordance with ASTM D-4546. 10 APPLIED PRESSURE - KSF 10 100 10 APPLIED PRESSURE - KSF 10 100 20-7-235 Kumar & Associates SWELL -CONSOLIDATION TEST RESULTS Fig. 4 SAMPLE OF: Sandy Silt and Clay FROM: Boring 2 © 2.5' WC = 7.1 %, DD = 113 pcf NO MOVEMENT UPON WETTING These test results apply only to the samples tested. The testing report shall not be reproduced, except in full, without the written approval of Kumar and Associates, Inc. Swell Consolidation testing performed in accordance with ASTM D-4546. 10 APPLIED PRESSURE - KSF 10 100 20-7-235 Kumar & Associates SWELL -CONSOLIDATION TEST RESULTS Fig. 4 Lot 93\Drafting \ HYDROMETER ANALYSIS SIEVE ANALYSIS TIME READINGS 24 HRS 7 HRS 45 MIN 15 MIN 60MIN 19MIN 4MIN 1MIN 4200 U.S. #100 &50 STANDARD #140 #30 SERIES # 6 #10 #8 #4 CLEAR SQUARE OPENINGS 3L8" 3/4" 1 1 2" 3" 51'6` 8"O 100 I I I 90 r I 10 I I I i i 80 i 20 I I I 70 1 30 I I I 1 60 40 g I 1 I c 50 I 1 1 50 1 1 1 2 d I I 1 40 1 1 60 d I I I I I 1 30 1 1 1 70 I I I 20 1 I i 80 I I I 1 10 90 1 I 0 .001 1 1 .002 .005 1 1 1 .009 1 .019 I .037 1 .075 .150 .300 DIAMETER OF PARTICLES I I I I .600 .425 1 1 1 1 1.18 IN 1 1 2.36 2.0 MILLIMETERS I I 1 1 1 1 1 4.75 9 1 5 19 1 1 1 1 1 1 1 1 1 38.1 76.2 127 152 200 100 SAND GRAVEL CLAY TO SILT FINE MEDIUM COARSE FINE COARSE COBBLES GRAVEL 51 % SAND 38 % SILT AND CLAY 11 LIQUID LIMIT PLASTICITY INDEX SAMPLE OF: Slightly Silty Gravel with Sand FROM: Boring 1 ® 5' These test results apply only to the samples which were tested. The testing report shall not be reproduced, except in full, without the written approval of Kumar & Associates, Inc. Sieve analysis testing is performed in accordance with ASTM D6913, ASTM D7928, ASTM C136 and/or ASTM D1140. 20-7-235 Kumar & Associates GRADATION TEST RESULTS Fig. 5 I(+A Kumar & Associates, Inc® Geotechnical and Materials Engineers and Environmental Scientists TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Project No. 20-7-235 SAMPLE LOCATION NATURAL MOISTURE CONTENT (%) NATURAL DRY DENSITYPASSING (pcf) GRADATION PERCENT NO. 200 SIEVE ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (psf) SOIL TYPE BORING DEPTH (ft) GRAVEL SAND LIQUID LIMIT (%) PLASTIC INDEX (%) 1 2 1/2 3.8 106 Sandy Silt and Clay 5 2.2 51 38 11 Slightly Silty Gravel with Sand 2 2 1/2 7.1 113 Sandy Silt and Clay 5 5.3 100 52 Very Sandy Silt and Clay