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HomeMy WebLinkAboutSoils Report 06.11.2020Kumar & Associates, Inc.® Geotechnical and Materials Engineers and Environmental Scientists An Employee Owned Company 5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa.eoM Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado SUBSOIL STUDY FOR FOUNDATION DESIGN PROPOSED RESIDENCE LOT 40, PINYON MESA CLIFFROSE WAY GARFIELD COUNTY, COLORADO PROJECT NO. 20-7-294 JUNE 11, 2020 PREPARED FOR: URIEL MELLIN 144 CLIFFROSE WAY GLENWOOD SPRINGS, COLORADO 81601 uriei.mellin()hofmail.com TABLE OF CONTENTS PURPOSE AND SCOPE OF STUDY - 1 - PROPOSED CONSTRUCTION - 1 SITE CONDITIONS - 1 - SUBSIDENCE POTENTIAL - 2 - FIELD EXPLORATION - 2 - SUBSURFACE CONDITIONS - 2 FOUNDATION BEARING CONDITIONS - 3 - DESIGN RECOMMENDATIONS - 3 - FOUNDATIONS - 3 - FOUNDATION AND RETAINING WALLS - 4 - FLOOR SLABS - 5 - UNDERDRAIN SYSTEM - 5 - SURFACE DRAINAGE - 6 - LIMITATIONS - 6 - FIGURE 1 - LOCATION OF EXPLORATORY BORING FIGURE 2 - LOG OF EXPLORATORY BORING FIGURE 3 - SWELL -CONSOLIDATION TEST RESULTS TABLE 1- SUMMARY OF LABORATORY TEST RESULTS Kumar & Associates, Inc. ® Project No. 20-7-294 PURPOSE AND SCOPE OF STUDY This report presents the results of a subsoil study for a proposed residence to be located on Lot 40, Pinyon Mesa, Cliffrose 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 Uriel Mellin dated May 21, 2020. Hepworth-Pawlak Geotechnical (now Kumar & Associates) previously performed preliminary geotechnical engineering studies for the subdivision development and presented the findings in reports dated November 11, 2005 and April 10, 2006, Job No. 105 652. A field exploration program consisting of an exploratory boring 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 proposed residence will consist of a one and partial two-story wood -frame structure over a crawlspace with an attached garage located as shown on Figure 1. The garage floor will be slab - on -grade. Grading for the structure is assumed to be relatively minor with cut depths between about 3 to 6 feet. We assume relatively light foundation loadings, typical of the proposed type of construction. If building location, grading or loading information are significantly different than described above, we should be notified to re-evaluate the recommendations presented in this report. SITE CONDITIONS The subdivision is located on a relatively flat topographic bench above the Roaring Fork River valley and below Spring Valley. Vegetation mainly consists of sage brush with juniper and pinyon trees further south of the lot. The front, north part of the lot appears to have been disturbed during road development. The ground surface of the building area appears mostly natural and is moderately sloping down to the north. Kumar & Associates, Inc. ® Project No. 20.7.294 -2 - SUBSIDENCE POTENTIAL Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Pinyon Mesa 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. Sinkholes were not observed in the subdivision but geologically young sinkholes are locally present in the evaporite region between Glenwood Springs and Carbondale and we are aware of several sinkhole collapses in this region during the past 10 years. No evidence of cavities was encountered in the subsurface materials; however, the exploratory boring was 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 40 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 May 26, 2020. One exploratory boring was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring was advanced with 4 -inch diameter continuous flight augers powered by a truck -mounted CME - 45B drill rig. The boring was logged by a representative of Kumar & Associates. Samples of the subsoils were taken with a 2 -inch I.D. spoon sampler. The sampler was 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 Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory for review by the project engineer and testing. SUBSURFACE CONDITIONS A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The subsoils, below a minor topsoil depth, consist of about 12 feet of stiff, sandy silt and clay overlying about 6 feet of medium dense, silty clayey sand with gravel overlying hard sandy clay below 18 feet underlain by dense clayey sand and gravel to the boring depth of 31 feet. The gravel content appeared to be siltstone fragments of the Eagle Valley Evaporite. Kumar & Associates, Inc. ® Project No. 20-7-294 -3 - Laboratory testing performed on samples obtained from the boring included natural moisture content and density and percent finer than sand size gradation analyses. Swell -consolidation testing on a relatively undisturbed drive sample of the upper silt and clay soil indicated low to moderate compressibility under conditions of loading and wetting. Results of swell -consolidation testing performed on a relatively undisturbed drive sample of the deeper clay soil indicated moderate expansion potential when wetted under a constant light surcharge. The test results are presented on Figure 3. The laboratory testing is summarized in Table 1. No free water was encountered in the boring at the time of drilling and the subsoils were slightly moist. FOUNDATION BEARING CONDITIONS The subsoils encountered on the lot at shallow depth consist of silt and clay which are typically known to be compressible when wetted under load. Lightly loaded spread footings can be used for support of the proposed residence provided that some risk of movement and distress is acceptable to the owner. A heavily reinforced mat foundation would help to make the structure more rigid and better able to resist differential settlement. Compacting the bearing soils to a depth of at least 3 feet below shallow footings is recommended help to reduce the settlement risk. Another alternative is a deep foundation system that extends the bearing level down to dense, low compressibility granular soils encountered at a depth of around 12 feet. If the deep foundation alternative is selected, we should be contacted for additional recommendations. DESIGN RECOMMENDATIONS FOUNDATIONS Considering the subsurface conditions encountered in the exploratory boring and the nature of the proposed construction, we recommend the building be founded with spread footings or a mat/structural slab bearing on compacted structural fill. The design and construction criteria presented below should be observed for a spread footing foundation system. 1) Shallow spread footings bearing less than about 8 feet below the existing ground surface should be placed on at least 3 feet of compacted structural fill. The structural fill can consist of the on-site silt and clay soils compacted to at least 98% of the maximum standard Proctor density at a moisture content near optimum. Based on experience, we expect initial settlement of footings designed and constructed as discussed in this section will be about 1 inch or less. There could be additional differential, post -construction foundation settlement on the order of 1 inch depending on the depth of any subsurface wetting. Precautions should be taken to keep the bearing soils dry. Kumar & Associates, Inc. ® Project No. 20.7.294 -4- 2) The footings should have a minimum width of 20 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. Shallow frost protection can consist of rigid foam insulation in the shallow mat foundation condition. 4) Foundations should be designed to be rigid with "box -like" configuration and isolated footings should be avoided. Continuous foundation walls should be heavily reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 14 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. 5) The topsoil, native soils to at least 3 feet below design bearing level and any loose or disturbed soils should be removed. The exposed soils in footing area should then be moistened and compacted. The structural fill should extend laterally beyond the footing edges a distance at least one-half the fill depth below the footing. 6) A representative of the geotechnical engineer should observe all footing excavations and test structural fill for 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 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. Kumar & Associates, Inc. ® Project No. 20-7-294 -5 - Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum standard Proctor density at a moisture content near 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 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 0.35. Passive pressure of compacted backfill against the sides of the footings can be calculated using an equivalent fluid unit weight of 325 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, can be used to support lightly loaded slab -on -grade construction. There is a risk of slab settlement and distress if the bearing soils become wetted. 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 interior 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 Although free water was not encountered during our exploration, it has been our experience in mountainous areas that local perched groundwater can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched Kumar & Associates, Inc. ® Project No. 20-7.294 -6 - condition. We recommend below -grade construction, such as retaining walls and basement areas (if provided), be protected from wetting and hydrostatic pressure buildup by an underdrain system. The slab -on -grade garage and crawlspace (up to around 4 feet deep) should not be provided with an underdrain system to better keep the shallow bearing soils dry. Where provided, the drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free -draining granular material. The drain should be placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimum 1% to a suitable gravity outlet. Free -draining granular material used in the underdrain system should contain less than 2% passing the No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel backfill should be at least 11/2 feet deep. An impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. SURFACE DRAINAGE Proper surface grading and drainage will be critical to keeping the bearing soils dry and limiting building settlement and distress. 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. Free -draining wall backfill should be covered with filter fabric and capped with about 2 feet of the on-site soils to reduce surface water infiltration. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least 10 feet from foundation walls. Consideration should be given to use of xeriscape to reduce the potential for wetting of soils below the building caused by irrigation. 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. ® Project No. 20.7-294 -7 - The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory boring drilled at the location 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 boring 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. Pawlak, Reviewed by: Daniel E. Hardin, P. E SLP/kac Cc: Patrick Stuckey (stucarch(d comcast.net) Adolfo Gorra (gsc@sopris.net) Kumar 8, Associates, Inc:. . Project No. 20=7-294 LOT 41 Ni<VW L 10 0 12 20 APPROXIMATE SCALE -FEET CLIFFROSE WAY LOT 40 i 6Y3rIrt'I000 LOT 39 20-7-294 Kumar & Associates LOCATION OF EXPLORATORY BORING Fig. 1 1- w w H d w 0 0 5 BORING 1 77) / 13/12 WC=5.7 DD=97 / 19/12 10 WC=3.6 /1 DD=106 -200=53 •:r 31/12 1 5:; WC=1.7 1 DD=110 -200=18 20 25 30 35 51/12 WC=4.1 DD=120 / 53/12 c•1 crl 77/12 LEGEND "dti. / TOPSOIL; ORGANIC SANDY SILT AND CLAY, BROWN. SILT AND CLAY (ML -CL); SANDY, SCATTERED GRAVEL, STIFF, SLIGHTLY MOIST, LIGHT BROWN, CALCAREOUS OR GYPSUM TRACES. SAND (SM -SC); SILTY, CLAYEY, GRAVELLY, MEDIUM DENSE, SLIGHTLY MOIST, BROWN. CLAY (CL); SANDY, HARD, SLIGHTLY MOIST, BROWN, MEDIUM PLASTICITY, SLIGHTLY CALCAREOUS. SAND AND GRAVEL (SC -GC); SILTY, CLAYEY, DENSE, SLIGHTLY MOIST, LIGHT BROWN, BEDROCK FRAGMENTS. hDRIVE SAMPLE, 2 -INCH I.D. CALIFORNIA LINER SAMPLE. 11/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 11 BLOWS OF A 140 -POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES. NOTES 1. THE EXPLORATORY BORING WAS DRILLED ON MAY 26, 2020 WITH A 4 -INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER. 2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED APPROXIMATELY BY TAPING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATION OF THE EXPLORATORY BORING WAS NOT MEASURED AND THE LOG OF THE EXPLORATORY BORING IS PLOTTED TO DEPTH. 4. THE EXPLORATORY BORING LOCATION SHOULD BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOG REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF DRILLING. 7. LABORATORY TEST RESULTS: WC = WATER CONTENT (%) (ASTM D 2216); DD = DRY DENSITY (pcf) (ASTM D 2216); -200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140). • 20-7-294 Kumar & Associates LOG OF EXPLORATORY BORING Fig. 2 CONSOLIDATION - SWELL 1 0 — 1 —2 — 3 — 4 4 3 J J W N 2 1 CONSOLIDATION 1 0 —1 2 SAMPLE OF: Sandy Silt and Clay FROM: Boring 1 ® 5' WC = 5.7 %, DD = 97 pcf :.t APPLIED PRESSURE - KSF 10 NO MOVEMENT UPON WETTING 100 SAMPLE OF: Sandy Clay FROM: Boring 1 ® 20' WC = 4.1 %, DD = 120 pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING These real mulls apply enty to the wmples tented. The tealinp report Mon not be reproduced, except in Irak, witheUt the written approval of leumm and Associates, Inc. scall Ca eatidetlen teeth, performed in eeeerdanee etch A IU D-1511. 1.0 APPLIED PRESSURE - KSF 10 100 20-7-294 Kumar & Associates SWELL—CONSOLIDATION TEST RESULTS Fig. 3 f[umar & Assoc9aies, Inc.° Geotechnical and Materials Engineers and Environmental Scientists TABLE 1 SUMMARY OF LABORATORY TEST RESULTS Proiect No. 20.7-294 SAMPLE LOCATIONGRADATION NATURAL MOISTURE CONTENT (lo) NATURAL DRY DENSITY (pcf) PERCENT 200 SIEVE PASSING NO. ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH (psf) SOIL TYPE BORING I DEPTH (Ft) GRAVEL o (/o ) SAND a) (/o LIQUID LIMIT (%) PLASTIC INDEX (%) 1- 1 5 5.7 97 Sandy Silt and Clay 10 ' 3.6 106 53 Very Sandy Silt and Clay with Gravel 15 1.7 110 18 Silty Clayey Sand with Gravel 20 4.1 120 Sandy Clay