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Home My WebLink AboutExcavation Observation 10.15.2001h October 15, 2001 Burkholder Construction Attn: Todd Burkholder 194 Cabin Drive Carbondale, Colorado 81623 Hepworth-Pawlak Geotechnical, Inc. 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970-945-7988 Fax: 970-945-8454 hpgeo@hpgeotech.com RECEIVED AUG 1 3 2018 GARFIELD COUNTY COMMUNITY DEVELOPMENT Job No. 101 689 Subject: Observation of Excavation, Proposed Residence, Lot GV -1, Aspen Glen Development, Garfield County, Colorado. Dear Mr. Burkholder: As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the excavation at the subject site on October 9 and 10, 2001 to evaluate the soils exposed for foundation support. The findings of our work and recommendations for the foundation design are presented in this report. The work was done in accordance with our agreement for geotechnical engineering services to Burkholder Construction, dated October 3, 2001. The proposed residence will be a two story wood frame structure over a partial basement and crawlspace. The attached garage and basement floors will be slab -on - grade. An allowable soil bearing pressure of 2,000 psf was assumed in the design. At the time of our initial visit to the site, the foundation excavation had been cut in three levels from 41/2 to 12 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation generally consisted of slightly silty sandy gravel with cobbles. Stiff sandy silty clay was exposed in the garage portion of the excavation. The clay was up to about 11 feet thick overlying the gravels in the garage footing trenches. We recommended via telephone that the clays in footing areas be subexcavated to expose the natural gravel soils. When observed on October 10, the garage footings had been deepened to expose the natural gravels. The garage slab area will be placed on the clays. Results of swell -consolidation testing performed on a sample of the clay taken from the site, shown on Fig. 1, indicate the soils have low compressibility under existing moisture conditions and light loading and a low collapse potential (settlement under constant load) when wetted. The sample showed high compressibility upon increased loading after wetting. 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 gravels designed for an allowable soil bearing pressure of 2,000 psf should be adequate for support of the proposed residence. 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 gravels. Burkholder Construction October 15, 2001 Page 2 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 10 feet. Foundation walls acting as retaining structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 45 pcf for on-site gravel, excluding oversized rock, as backfill. A perimeter foundation drain should be provided to prevent temporary buildup of hydrostatic pressure behind the walls and prevent wetting of the basement level. The natural sandy clay should be suitable for support of the garage slab. The clay soils exposed in the garage slab area tend to compress when wetted and there could be some post -construction settlement of the slab if the bearing soils become wet. Structural fill placed within floor slab areas can consist of the on-site gravels compacted to at least 95 % of standard Proctor density at a moisture content near optimum. Backfill placed around the structure should be compacted and the surface graded to prevent ponding within at least 10 feet of the building. 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. If there are any questions or if we may be of further assistance, please let us know. Sincerely, HEPWORTH - PAWLAK GEOTECHNICAL, INC. Jordy Z. Adamson, Jr., P.E. Rev. by: DEH JZA/ksw attachment cc: Mike Thele Structural Engineering Services - Attn: Mike Thele H -P GEOTECH 0.1 101 689 1.0 10 APPLIED PRESSURE — ksf HEPWORTH-PAWLAK GEOTECHNICAL, INC. SWELL CONSOLIDATION TEST RESULTS 100 Fig. 1 COCompressionA— Expansion % i 1 J _. J J J _ co W •—.11 T Q) Cn W N f, 0 W Ui W ra O If Moisture Content = 10.5 percent Dry Derisily = 87.2 pct Sample Sandy Silty Clay of: From: Bottom of Excavation—Garage Area Compression upon wetting I C \C/ J 0.1 101 689 1.0 10 APPLIED PRESSURE — ksf HEPWORTH-PAWLAK GEOTECHNICAL, INC. SWELL CONSOLIDATION TEST RESULTS 100 Fig. 1