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HomeMy WebLinkAboutObservation of Excavation 10.18.2013Gtech HEPWORTH-PAWLAK GEOTECHNICAL October 18, 2013 Jesus Molina 492 County Road 240 Glenwood Springs, Colorado (tnolinajesus5 rr hotmail.com) I{rrwonla I',nlhi, iir+rcil'II tc I, Inc. -;020 1-i i ii[ V,0,1,1 1 ilL'IIUt++h1 SpinQw. chit) SI GL i I91 +1R-: 97!:.'r l; r+.i.,. Fax; 9r0 -94S S4i4 rllldll: ofPhpgo+Decl.Com Job No. 113 361A Subject: Observation of Excavation, Proposed Residence, Lot 3, Turgoose Ranch Subdivision, Home Ranch Road (CR 293), Northeast of Rifle, Garfield County, Colorado Dear Mr. Molina: As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the excavation at the subject site on October 11, 2013 to evaluate the soils exposed for foundation support. The findings of our observations and recornrnendations for the foundation design are presented in this report. The services were performed in accordance with our agreement for professional engineering services to you, dated September 23, 2013. The project includes the construction of a modular type residential structure on the lot. The modular structure will be founded on concrete strip footings. Minimal cuts of 1 to 3 feet in depth are anticipated for the construction. Structural plans by Westar Civil and Structural Engineers, dated October 10, 2013, were reviewed at the time of our site visit. The structural plans indicated that the footings for the structure have been designed utilizing an assumed soil bearing pressure of 1,500 psf. At the time of our visit to the site, the foundation excavation had been cut in one level from 1 to 3 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation consisted of slightly sandy silty clay. Results of swell -consolidation testing performed on samples taken from the site, shown on Figure 1, indicate the soils are moderately compressible under conditions of loading and wetting. No free water was encountered in the excavation and the soils were moist at the time of our visit due to recent rains. 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 1,500 psf should be adequate for support of the proposed residence. The exposed soils tend to compress when wetted and there could be some post -construction settlement of the foundation if the bearing soils become wet. Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns. Loose and disturbed soils in footing areas should be removed and the bearing Parker 303-541-7119 • Colorail' gs 719-633-5562 • Silverthorne 970-468-1989 Jesus Molina October 18, 2013 Page 2 level extended down to the undisturbed natural soils. The bearing soils should be protected against frost and concrete should not be placed on frozen soils. Exterior footings should be provided with adequate soil cover above their bearing elevations for frost protection, typically 36 inches of cover in this area. 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 (if any) 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 as backfill. Structural fill placed within slab - on -grade areas can consist of the on-site 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. Landscape that requires regular heavy irrigation, such as sod, and sprinkler heads should not be located within 10 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 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 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, HEPRTH — PAWL I GEOTECHNICAL, INC. rovuiw.„,„„„ /,,4, fe ,„ .0 REQ/. if ....e James A. Parker, P.E, P.G. a Reviewed by: ▪ ▪ p t4 ©,1.9s: /3 Daniel E. Hardin, P.E. .�Q,�e °+°rrrNrrrr\�t?� ii'/f`i +u10NALytNG``�`� JAP/ljg attachments Figure 1 — Swell Consolidation Test Results cc: Carlos Sanchez (sanchez.carlos220 r�gmail.colm) Job No. 113 361A Gtech Compression - Expansion % Compression - Expansion % 0 1 2 3 4 0 1 2 3 4 5 6 7 Moisture Content = 15.7 percent Dry Density = 112 pcf Sample of: Sandy Clay From: NW Corner of Foundation Excavation Compression upon wetting 0.1 1.0 0 APPLIED PRESSURE - ksf 100 Moisture Content = 16.7 Dry Density = 105 Sample of: Sandy Clay From: SE Corner of Foundation Excavation percent pcf Compression upon wetting 0.1 1.0 10 APPLIED PRESSURE - ksf 113 361A H Hepworth—Pawlak Geotechnicol SWELL -CONSOLIDATION TEST RESULTS • 100 Figure 1