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HomeMy WebLinkAboutObservation of Excavation Report 06.09.1998HEPWORTH-PAWLAK GEOTECHNICAL, INC. July 9, 1998 Leonard Construction Attn: Rock Leonard 1101 Village Road, Suite UL3D Carbondale, Colorado 81623 RECEIVED MAR 2 3 2018 GARFIELD COUNTY COMMUNITY DEVELOPMENT 5020 Road 154 Glenwood Springs, CO 81601 Fax 970 945-8454 Phone 970 945-7988 Job No. 198 470 Subject: Observation of Excavation, Proposed Residence, Lot 7, Wooden Deer Subdivision, 805 Wooden Deer, Garfield County, Colorado Dear Mr. Leonard: As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the excavation at the_ subject site on July 8, 1998 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 you, dated July 7, 1998. The proposed residence will be a two story concrete and wood frame structure over a walkout basement level. The basement floor will be slab -on -grade. Concrete foundations were designed based on an assumed soil bearing pressure of 2,000 psf. At the time of our visit to the site, the foundation excavation had been cut in two main Ievels from 6 to 15 feet below the adjacent ground surface, The soils exposed in the bottom of the excavation consisted primarily of basalt cobbles and boulders up to 5 feet in size with a calcareous gravelly sandy clay matrix. The soils exposed in the southwest corner of the excavation consisted of hard cemented silty sand. No free water was encountered in the excavation and the soils were slightly moist to dry. 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 soil bearing pressure of 2,000 psf should be adequate for support of the proposed residence. The clay matrix soils tend to compress when wetted and there could be some post -construction movement of the foundation if the bearing soils become wet. 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. 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 50 pcf for on-site soil as backfill, excluding vegetation, topsoil and oversized rock. A perimeter foundation drain should be provided to prevent temporary buildup of hydrostatic pressure behind the walls and prevent wetting of the lower level. Structural fill placed within floor slab areas can 'hard C onstr 1u1, 9, 1998 I'ise2 consist of the on-site soils compacted- to at least 95 % of standard Proctor density at a moisture content hear optimum, Backfill placed around the structure should be compacted and the surface «,railed to prevent ponding within at least 10 feet of the huilding. The recommendations submitted in his tetter 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 !here are any questions or if we may he of further assistance, please let us know. 4iocdrely Ilardin. P. H -P C'