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Home My WebLink AboutB14-0207 GeoTech letter.pdfJuly3l,2014 Revised August 4, 2014 Arrigoni Woods Attn: Coleman Wise P. 0. Box 1057 Minturn, Colorado 81645 Job No. 114 294A Subject: Observation of Excavation, Proposed Garmisch Haus Residence, Lots 27 and 28, Block A, Filing 3, Vail Das Schone, 2476 Garmisch Drive, Vail, Colorado, Dear Coleman: As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the excavation at the subject site on July 29, 2014 to evaluate the soils exposed for foundation supp01i. The findings of our observations and recommendations for the foundation design are presented in this report. The services were performed in accordance with our agreement for professional engineering services to Arrigoni Woods, dated July 25, 2014. The residence will be a 1 Yi to 2 story wood frame structure over a basement level with slab-on-grade ground floors. The building has been designed to be supported on spread footings assuming an allowable soil bearing pressure of 1,500 psf. At the time of our site visit, the foundation excavation had been cut in multiple levels from about 4 to 8 feet below the adjacent ground surface. Steps in grade between the levels ranged from 21!2 to 31!2 feet. The soils exposed in the bottom of the excavation consisted primarily of relatively dense, clayey silty sandy gravel with cobbles. In the northeast po1iion of the excavation was an apparent shallow depth of old fill that we recommended be removed. The excavation subgrade had been compacted. The soils were too 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 5 inch fraction) obtained from the site arc presented on Figure 1. No free water was encountered in the excavation and the soils were slightly moist to moist. Considering the conditions exposed in the excavation and the nature of the proposed construction, spread footings placed on the undisturbed natural granular soil designed for an allowable bearing pressure of 1,500 psf can be used for support of the proposed building. The fine grained matrix soils could compress when wetted and precautions should be taken to keep the bearing soils dry and limit future building settlement. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. All fill and loose disturbed soils in footing areas should be removed and the bearing level extended down to the undisturbed natural granular soils. Exterior footings should be provided with adcqw.ite soil cover above their hearing elevations for frost Arrigoni Woods July 31, 2014 Revised August 4, 2014 Page 2 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 pcf for on-site soil, excluding topsoil and oversized rocks, as backfill. A perimeter foundation drain should be provided to prevent temporary buildup of hydrostatic pressure behind the basement walls and prevent wetting of each below grade level. The underdrain system should include at least 4 inches of free draining gravel below the basement floor slab. Structural fill placed within floor slab areas can consist of the on-site sand and gravel soils compacted to at least 95% of standard Proctor density (SPD) at a moisture content near optimum. Backfill placed around the structure should be compacted to at least 90% SPD and the surface graded to prevent ponding within at least l 0 feet of the building. Landscape that requires regular heavy irrigation, such as sod, and sprinkler heads should not be located within 5 feet of the 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 !,'Teater 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 dete1mining 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. If you have any questions or need further assistance, please call our office. Sincerely, DAY/ksw attachment Joh No. 114 294A ~tech I HYDROMETER ANALYSIS I SIEVE ANALYSIS I I TIME READINGS I U.S. STANOARD SERIES I CLEAR SQUARE OPENINGS I 24HR. 7HR 45MIN. 15MIN. 61lMIN. 19MIN. 4MIN. 1 MIN. 1200 #100 #50 #30 #16 #8 #4 31/f' 3/'t 1112' 3" 5• If If 0 100 10 90 20 80 30 70 0 40 60 CJ w z z ~ ~ a: 50 50 0.. I-I-z z w -w () () a: a: w w 0.. 60 40 Cl. 70 30 80 20 90 10 100 0 .001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36 4.75 B.5 12.5 19.0 37.5 762 127152 203 DIAMETER OF PARTICLES IN MILLIMETERS SANO CLAY TO SILT I MEDIUM FINE GRAVEL I I COBBLES FINE COARSE Gravel 46 % Sand 31 % Silt and Clay 23 % Liquid Limit % Plasticity Index % Sample of: Silty Sandy Gravel with Cobbles From: Bottom of Excavation 114 294A ~tech GRADATION TEST RESULTS FIGURE 4 HEPWORTH-PAWLAK GEOTECHNICAL