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HomeMy WebLinkAboutSoils Report.pdfHEPWORTH-PAWLAK GEOTECHNICAL, INC. August 10, 1993 Larry and Dawn Thrun P.O. Box 883 Silt, Colorado 81652 7840 Highway 82 Glenwood Springs, CO 81601 Fax 303 945-8454 Phone 303 945-7988 Job No. 193 151 Subject: Observation of Excavation, Proposed Residence, 8000 County Road 117, Garfield County, Colorado. Dear Mr. and Mrs. Thrun: As requested, Hepworth-Pawlak Geotechnical, Inc. observed the excavation at the subject site on July 29 and August 4, 1993 to evaluate the soils exposed for foundation support. The fmdings 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 Larry and Dawn Thrun, dated July 29, 1993. The proposed residence will be a 1 1/2 story wood frame structure above a walk out basement level. The garage will be on the upper main level. At the time of our initial visit to the site, the foundation excavation had been cut in two levels from 1 to 6 feet below the adjacent ground surface. The garage and basement areas essentially daylighted to the west from their respective excavation levels. The soils exposed in the bottom of the excavation were variable and consisted mainly of clayey gravel with cobbles and boulders in the lower level and soft wet clays in the upper (garage) level. The northwest corner of the basement frost depth footing trench was based in organic sandy clay. Probing with a steel rod indicated the clay depth is 1 to 3 feet in the garage area and one foot in the northwest basement corner below footing cut grade. Results of consolidation testing performed on samples taken from the site, shown on Fig. 1, indicate the clay soils are moderately to highly compressible under conditions of loading and wetting. The test results are summarized in Table I. Most of the excavation was cut below the groundwater level, and drain gravel and perforated pipes had been installed to collect and divert the water seepage to the north of the building. The clays in the garage area were generally soft and wet and it was recommended to construct an intercept trench drain just uphill of the garage. When Larry and Dawn Thrun August 10, 1993 Page 2 observed on August 4, the trench drain had been installed and the water seepage flow in the garage footing area had essentially stopped. The water seepage from the uphill basement cut had also diminished from that observed on July 29. Considering the conditions exposed in the excavation and the nature of the proposed construction, spread footings placed on the undisturbed natural soils and drain gravel backfill designed for an allowable soil bearing pressure of 1500 psf should be adequate for support of the proposed residence. The wet black clays in the garage area should be subexcavated and replaced with drain gravel. The gravel backfill should extend 1 to 2 feet beyond the edge of the footing. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. Loose and disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footings 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 12 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 granular soil backfill (excluding rock greater than 8 inches). A perimeter foundation drain should be provided to prevent temporary buildup of hydrostatic pressure behind the walls and prevent wetting of the lower level. The drain gravel should extend to above the line of wetting in the excavation face. Garage floor backfill can consist of the on-site gravelly soils 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. H -P GEOTECH Larry and Dawn Thrun August 10, 1993 Page 3 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. Steven L. Pawlak, SLP/ro Attachment H -P GEOTECH -alj S11f1S3d 1S31 NOI1V0I1OSNO0-113MS oil '1V3INH33103J )IV1MVd-HJiJOMd3H 1.91. £61, is)l — 31:1f1SS3 dd 0311ddV oat Ot 01 t'0 5 b £ 6uiTIeM uoissaadwop uodn Compression % N — 0 NO, aullooj aauaoo ARID &'puss wawaseq ;saran-low :wo d oIUe6JQ pd wowed b• 96 t to aidwes = 1t13 aM pun Ain = luatuo3 alnlsiotiy 0ot )S)1 — 31:1f1SS9EJd 0311ddV of (it c0 0 E 0 ID ID 6ulllan uodq quawanoW ON in 0 .6-g + I 6ulgooj abeieb IIPM Banos :wo J API3 £2IIS 0 :loaldwes lad LOI = 146iaM pull Aio luaaJad I, • 61, = lualuo3 a)nls!on 0) c 0 m r D 0 —1 OD W —DIm O - cn N r cncn o w 0 m 0 J 01 J HEPWORTH-PAWLAK GEOTECHNICAL, INC. Northwest Corner Basement Footing South Wall Garage Footing North Wall Garage Footing SAMPLE LOCATION N_ :piO Na co 11 NATURAL MOISTURE CONTENT (%) co O O V co co NATURAL DRY DENSITY (pcf) c m r•0 0 Z Z N .R2 0 PERCENT PASSING NO. 200 SIEVE . "' i 5 4 O 1 ATTEBBERG LIMITS 2 deON UNCONFINED COMPRESSIVE STRENGTH IPSFI organic sandy clay silty clay organic silty clay SOIL OR BEDROCK TYPE 0) c 0 m r D 0 —1 OD W —DIm O - cn N r cncn o w 0 m 0 J 01 J HEPWORTH-PAWLAK GEOTECHNICAL, INC.