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Home My WebLink AboutB14-0129 Soils report.pdf1,°\ Hp,1,„\1,1 GeOteCh 1,,,,., HEPWORTH-PAWL.AK GEOTECHNICAL 1 ,, 0„"); , lir May 20, 2014 SRE Building Associates Ben Biggs 23698 Highway 24 Minturn, Colorado 81645 ben@),srebuilds.com Job No. 114 116A Subject: Observation of Excavation, Proposed Addition to Landers Residence, Lot 1, Glen Lyon, 1454W Greenhill Court, Vail, Colorado Dear Ben: As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the excavation at the subject site on May 15, 2014 to evaluate the soils exposed for foundation support. The findings of our observations and recommendations for the foundation design are presented in this report. The services were performed in general accordance with our agreement for professional engineering services to SRE Building Associates, dated April 15, 2014. The addition will be attached to the northeast side of the existing residence and be one story of wood frame construction over a basement level. The basement floor will be slab- on-grade. The addition has been designed to be supported on spread footings assuming an allowable soil bearing pressure of 2,000 psf. The existing residence is apparently founded on shallow spread footings with no signs of excessive settlement and distress reported. At the time of our site visit, the foundation excavation for the addition was nearly complete and had been cut in three levels from about 6 to 8 feet below the adjacent ground surface. The extreme northwestern portion of the excavation was not complete. The excavation subgrade was generally at about the same elevation as the existing building spread footing bearing elevation. The soils exposed in the bottom of the excavation consisted of medium dense, clayey sand with gravel. The soils were to rocky to obtain undisturbed samples for swell-consolidation testing. The results of a gradation analysis performed on a disturbed bulk sample of the soils(minus 3 inch fraction) I'drker i0i-841-71 1t) • in , 1 )-633-5562 • Silvertliorne 970.465-19$t) SRE Building Associates May 20,2014 Page 2 obtained from the site are presented on Figure 1. No free water was encountered in the excavation and the soils were generally moist. Considering the conditions exposed in the excavation and the nature of the proposed construction, spread footings placed on the undisturbed natural soil designed for an allowable bearing pressure of 1,500 psf can be used for support ofthe proposed addition. There could be some differential settlement with respect to the existing structure which should be considered in the design. The footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed soils in footing areas should be removed and the bearing level extended down to the undisturbed natural soils and the subgrade compacted. Exterior footings should be provided with adequate soil cover above their bearing elevations for frost protection. 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 a lateral earth pressure based on an equivalent fluid unit weight of at least 50 pef for on-site soil as backfill. A perimeter foundation drain should be provided to prevent temporary buildup of hydrostatic pressure behind the basement walls and prevent wetting ofthe lower level. The underdrain system should include at least 4 inches of free draining gravel below the basement floor slabs. Structural fill placed within floor slab areas can consist of the on-site soils compacted to at least 95% of standard Proctor(SPD)density at a moisture content near optimum. Backfill placed around the structure should be compacted to at least 90%SPD (95%in pavement areas) and the surface graded to prevent ponding within at least 10 feet of the building. Landscape that requires regular heavy irrigation, such as sod, and sprinkler heads should not be located within 5 feet ofthe foundation. The recommendations submitted in this letter are based on our observation of the soils exposed within the foundation excavation and do not include subsurface exploration to evaluate the subsurface conditions within the loaded depth of foundation influence. This study is based on the assumption that soils beneath the footings have equal or better support than those exposed. The risk of foundation movement may be greater than indicated in this report because of possible variations in the subsurface conditions. In order to reveal the nature and extent of variations in the subsurface conditions below the excavation, drilling would be required. It is possible the data obtained by subsurface exploration could change the recommendations contained in this letter. Our services do not include determining the presence,prevention or possibility of mold or other biological Job No. 114 116A Ge ech SRE Building Associates May 20, 2014 Page 3 contaminants(MOBC)developing in the future. Ifthe client is concerned about MOBC, then a professional in this special field of practice should be consulted. If you have any questions or need further assistance, please call our office. Sincerely, HEPWORTH—PAWLAK GEOTECHNICAL, INC. 011111//ho,1a 2 : ,y David A. Young, P.E. y 216 vs DAY/ksw iii t: 4$2`.. 1/1/HI N0" e attachment Figure 1, Gradation Test Results lob No 1 14 1 1M Gecgtech