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HomeMy WebLinkAboutDRB140188_soil_report_1401226200.pdfPRELIMINARY SOIL AND FOUNDATION INVESTIGATION FOR A PROPOSED RESIDENCE LOT 8, BIGHORN SUBDIVISION 3816 LUPINE DRIVE EAST VAIL EAGLE COUNTY, COLORADO PROJECT NO. 14-2930 MAY 22, 2014 PREPARED FOR: Chateau d’Oex LLC, a Colorado limited liability company P.O. Box 2837, Edwards, CO 81632 Tel (970) 926-9088 TABLE OF CONTENTS EXECUTIVE SUMMARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 SCOPE OF STUDY.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 SITE DESCRIPTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 PROPOSED CONSTRUCTION.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 FIELD INVESTIGATION.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 SUBSURFACE SOIL AND GROUNDWATER CONDITION.. . . . . . . . . . . . . . . . . . . . . . . . . 3 FOUNDATION RECOMMENDATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 SLAB CONSTRUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 RETAINING WALLS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 UNDERDRAIN SYSTEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 SITE GRADING AND DRAINAGE. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 LAWN IRRIGATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 LIMITATION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-9 FIGURES LOCATION SKETCH . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . .DRAWING NO. 1 SUBSURFACE EXPLORATION LOGS. . . . . . . . . . . . . . . . . . . . . . . . . . .FIGURE NO’s 1-2 SWELL-CONSOLIDATION . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . .FIGURE NO. 3-5 PERIMETER DRAIN DETAIL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .FIGURE NO. 6 OVEREXCAVATION AND COMPACTION DETAIL. . . . . . . . . . . . . . . .FIGURE NO. 7 P.O. Box 2837, Edwards, CO 81632 Tel (970) 926-9088 EXECUTIVE SUMMARY Based on the preliminary information from the two test pits, the proposed residence can be supported with conventional type spread footings, designed for an allowable soil bearing pressure of 2500 psf. They should construct the footings on the undisturbed, light brown, silty, clayey sand with angular rock fragments, below the organic layer and topsoil, encountered at about 9.5 feet below the existing grade. See Foundation Recommendations. SCOPE OF STUDY This report presents the Preliminary results of a subsurface Soil and Foundation Investigation for a proposed residence to be constructed on Lot 8, Bighorn Subdivision, 3816 Lupine Drive, East Vail, Eagle County, Colorado. The purpose of the subsurface soil and foundation investigation was to determine the engineering characteristics of the foundation soil and to provide recommendations for the foundation design, grading, and drainage. Geologic Hazard Studies are outside of our scope of services. SITE DESCRIPTION Lot 8, is a 0.869-acre lot, at 3816 Lupine Drive, on the south side of the road in East Vail, Eagle County, Colorado. The selected building site was at the base of a steep slope. Vegetation on the lot consisted of aspen forest on the flatter portion of the lot and pine forest with brush on LKP Engineering, Inc. 3 the steeper. There were large boulders on the site. There was also a small amount of snow. Drainage was to the north. PROPOSED CONSTRUCTION We understand that the proposed residence will be a three-story, log construction, on a concrete foundation with a walkout garage/basement. We anticipate loads to be light to moderate, typical of residential construction. If the finalized plans differ significantly from the above understanding, they should notify us to re-evaluate the recommendations of this report. FIELD INVESTIGATION The field investigation, conducted on April 25, 2014, consisted of excavating, logging and sampling two test pits. The excavation of the test pits was done by you with a trackhoe. Soil and foundation investigation with a drill rig was discussed, and it is still recommended. The test pits’ locations are shown on Drawing No. 1. We show the soil profile of the test pits on the Subsurface Exploration Logs, Figure No’s 1 and 2. Soil samples for laboratory soil analysis and observation were taken at selected intervals. SUBSURFACE SOIL AND GROUNDWATER CONDITION The soil profiles encountered in the two test pits were fairly uniform. Test Pit No. 1 had about four feet of topsoil with large boulders over brown to dark brown and moist, sand with organics over to the maximum depth explored of 7.5 feet. Refusal on boulders was encountered at 7.5 feet. Test Pit No. 2 had about 6 feet of topsoil and dark brown clayey sand with topsoil and roots over 3.5 feet of moist, dark brown, clayey sand over 1.5 feet of light brown, clayey sand. LKP Engineering, Inc. 4 There were no boulders in test pit number two. Ground water was not encountered in either test pit, but the soils had high moisture content. We sampled the soil in the test pits at random intervals. The soil samples were tested in our laboratory for swell-consolidation, natural dry density and natural moisture content. The test results are shown on Figure No’s 3 - 5. PRELIMINARY FOUNDATION RECOMMENDATIONS Additional soil and foundation investigation with a drill rig is recommended. Based on the depth where suitable bearing material was found, a deep foundation system, like straight shaft piers or micro piles, might be more suitable for this site. The proposed residence can be supported with conventional type spread footings, designed for a maximum allowable soil bearing pressure of 2500 psf. The footings should be constructed on the undisturbed light, light brown, clayey sand. The light brown clayey sand was encountered at about 9.5 feet in Test Pit Number 2. We recommend a minimum width of 16 inches for the continuous footings and 2 feet for the isolated footing pads. Continuous foundation walls should be reinforced top and bottom to span an unsupported length of at least 10 feet. We recommend a minimum of 48 inches of backfill cover for frost protection of the footing subsoils. The foundation excavation should be observed by the undersigned engineer to verify that the soil conditions encountered during construction are as anticipated in this report. The foundation excavation should be free from excavation spoils, frost, organics and standing water. We recommend proof-rolling of the foundation excavation with light equipment. Heavy equipment can bring up the moisture from the underlaying soils and create soft and unsuitable base for the foundation. Soft spots detected during the proof-rolling, should be removed by overexcavation. Any overexcavation within the proposed foundation, should be backfilled, in 8 inches loose level lifts and compacted to 100% of the maximum dry density and within 2 percent LKP Engineering, Inc. 5 of the optimum moisture content as determined in a laboratory from a Standard Proctor test (ASTM D-698). A structural fill, placed under footings should be tested by a qualified professional on regular basis. As another alternative, the proposed log home can be supported on a structural fill with conventional type spread footings, designed for a maximum allowable soil bearing pressure of 2000 psf. The existing unsuitable soil will be overexcavated a minimum of four feet below the proposed bottom of footing elevation and backfilled with compacted, structural fill. The width of the overexcavation should be according to the attached overexcavation and compaction detail. The structural fill can be minus 3-inch road base or other, suitable material approved by the engineer. We also recommend that a Tensar triaxial geogrid be placed in the structural fill. The first layer of geogrid should be placed 6 inches above the compacted subgrade. The next two layers should be placed at 1.5 feet apart with a 6-inch backfill material above the last geogrid layer. SLAB CONSTRUCTION The upper soils encountered in the two test pits consisted of topsoil, which is not suitable for a slab on grade construction. The natural, light brown, clayey sand encountered in test pit number two at 9.5 feet is suitable to support lightly loaded slab-on-grade construction. The subgrade for the slab-on-grade construction should be proof compacted to detect and remove soft spots. They should backfill overexcavated soft spots and other underslab fill with the on-site soil, free from topsoil and organics, or other suitable material, compacted to a minimum of 95 percent of the maximum standard Proctor density (ASTM D-698). Suitable material should be free from topsoil, organics and rock fragments greater than 3 inches. The concrete slab should be constructed over a 4-inch layer of clean gravel consisting of - 3/4 inch gravel with at least 50% retained on the No. 4 sieve and less than 3 percent passing the No. 200 sieve. LKP Engineering, Inc. 6 They should reinforce the concrete slab-on-grade and score control joints according to the American Concrete Institute requirements and per the recommendations of the designer to reduce damage due to shrinkage. The concrete slab should be separated from the foundation walls and columns with expansion joints to allow for independent movement without causing damage. If the entire slab is not within the suitable soil, three feet of the underslab soil will be removed and replaced according to the overexcavation and compaction recommendations in the Foundation recommendation section above. As another alternative a structural floor over a crawl space can be designed and constructed. RETAINING WALLS Foundation walls retaining earth and retaining structures that are laterally supported should be designed to resist an equivalent fluid density of 60 pcf for an “at-rest” condition. Laterally unrestrained structures, retaining the on-site earth, should be designed to resist an equivalent fluid density of 40 pcf for the “active” case. Passive earth pressure of 350 psf can be used for the lateral pressure against the sides of the footings. Resistance to sliding at the bottom of the footings can be calculated based on a coefficient of friction of 0.35. Undisturbed soil or a structural fill compacted to 100 percent of the maximum dry density and within 2 percent of the optimum moisture content shall be used to resist lateral loads at the sides of the footings. The above design recommendations assume drained backfill conditions and a horizontal backfill surface. Surcharge loading due to adjacent structures, weight of temporary stored construction materials and equipment, inclined backfill and hydrostatic pressure due to undrained backfill should be incorporated in the design. They should try to prevent the buildup of hydrostatic pressure behind the retaining wall. LKP Engineering, Inc. 7 UNDERDRAIN SYSTEM To reduce the risk of surface water infiltrating the foundation subsoil, we recommend installation of a foundation perimeter drain (see Figure No. 6). The foundation perimeter drain should consist of a 4-inch diameter, perforated pipe, sloped to a suitable gravity outlet, or to a sump pump location, at a 1/4 inch per foot for flexible or at a 1/8 of an inch for rigid pipe. The bottom of the trench adjacent to the footing should be lined with a polyethylene moisture barrier glued to the foundation wall. The drain pipe should be covered with a minimum of 6 inches of - 3/4-inch free-draining granular material. Geotextile (Mirafi 140N or equivalent) should be used to cover the free-draining gravel to prevent siltation and clogging of the drain. The backfill above the drain should be granular material to within 2 feet of the ground surface to prevent a buildup of hydrostatic pressure. SITE GRADING AND DRAINAGE The following recommendations are general. Exterior backfill should be compacted at or near the optimum moisture content to at least 95% of the maximum standard Proctor density under pavement, sidewalk and patio areas and to at least 90% of the maximum standard Proctor density under landscaped areas. They should use mechanical methods of compaction. Do not puddle the foundation excavation. The site surrounding the building structure should slope away from the building in all directions. A minimum of 12 inches in the first 10 feet is recommended in unpaved areas, and three inches in the first 10 feet in paved areas. The top of the granular foundation backfill should be covered with a minimum of 1 foot of relatively impervious fill to reduce the potential of surface water infiltrating the foundation subsoils. LKP Engineering, Inc. 8 Permanent, unretained cut and fill slopes should be graded at two horizontal to one vertical or flatter with slope heights not exceeding 20 feet. Slopes exceeding 20 feet should have benching incorporated. To protect the newly created slopes, erosion control methods should be used. Also, drainage of the site above the slopes should be controlled to prevent slope instability. Surface water naturally draining toward the proposed building site should be diverted around and away from it by means of drainage swales or other approved methods. The roof drains and downspouts should extend and discharge beyond the limits of the backfill. LAWN IRRIGATION It is not recommended to introduce excess water to the foundation soils by installing sprinkler systems next to the building. The installation of the sprinkler heads should insure that the spray from the heads will not fall within 10 feet of foundation walls, porches or patio slabs. Lawn irrigation must be controlled. LIMITATION This report is preliminary. Additional soils and foundation investigation with a drill rig is recommended. This report has been prepared according to locally accepted Professional Geotechnical Engineering standards for similar methods of testing and soil conditions at this time. There is no other warranty either expressed or implied. The findings and recommendations of this report are based on field exploration, laboratory testing of samples obtained at the specific locations shown on the Location Sketch, Drawing No.1 and on assumptions stated in the report. Soil conditions at other locations may vary, which may not become evident until the foundation excavation is completed. If soil or water conditions seem different from those described in this report we should be contacted immediately to reevaluate the recommendations of this report. LKP Engineering, Inc. 9 This report has been prepared for the exclusive use of Chateau d’Oex LLC, a Colorado limited liability company, for the specific application to the proposed residence on Lot 8, Bighorn Subdivision, 3816 Lupine Drive, East Vail, Eagle County, Colorado. Sincerely, LKP ENGINEERING, INC. ________________________ Luiza Petrovska, PE J:\_WP X4-LKP\_2014\14-2930cl-sndPrelim.RPT.wpd LKP Engineering, Inc.