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Home My WebLink AboutObservation of Excavation for Original Dwelling, Burnt Down in Fire 11.30.1999November 30 Ralph Besler 0025 Road 116 Glenwood Springs, Colorado 81601 Hepworth-Pawlak Geotechnical, Inc, 5020 County Road 154 Glenwood Springs, Colorado 81601 Phone: 970-945-7988 Faxz 970-945-M54 hpgeo@hpgeotech.com Job No. 199 921 H Subject:Observation of Excavation, Proposed Residence, L962Road t32, Garfield County, Colorado. Dear Mr. Besler As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the excavation at the subject site on November 24, 1999 to evaluate the soils exposed for foundatiqn support. The findings of our work and recommendations for the foundation desigp are.presented in this report. The work was done in accordance with our agreement for geotechnical engineering services to you, dated November 24,1999. The proposed residence will be a lVz story wood frame structure over a walkout basement level.' 'We understand that possibly a monolithic slab foundation will be used. An allowable bearing capacity oJISO0 ps:lwæ assumed in the design of spread footings. The site is relatively flat w-ähæIight slope down to the west. The terrain is steep to the east of the building area. At the time of our visit to the site, the foundation excavation had been cut in one level up to 6 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation consisted of sligbtly silty sandy gravel with cobbles and occasional boulders. Up to 4 feet of backfill ftom the building to the north was exposed in the northçrn cut face. The results of ¿oþadation analysiJperformed on a sample of the gravels (minus 5 inch fraction) obtaioed from the site are presented on Fig. l. 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 natt¡ral soil designed for an allowable soil bearing pr€ssure of.åU!-¡¡¡f¡an be used for support of the proposed residcnce. Footings should be a minimum width of 16 inches for continuous walls and 2 fe*t for coh¡mns. loose and disturbed soils in footing areas shot¡ld be moisæned and compacted or removed and the bearing level extended down to the undistr¡tbed natural gravels. Voids created by removal of large rocks should be backfilled with compacted sand and gravel or with concrete. Exterior footings should be provided with adequate soil cover above their bearing elevations for frost protection. Continuous foundation walls shoutd be heavily reinforced top aod bottom to span local anorrralies and limit the effects of differential settlement such as by assuming ari unsupported lengfh of at least 10 feet. Foundation walls acting ¿s ¡staining stn¡chrres should be designed to resist a lateral earth pressure based on aû equivalent fluid unit weight of at least 45 pcf for on-site gravels, excluding oversized rock, as backfill. A perimeter foundation drain should be provided to preveft tempomry buildup of hydrostatic pressure behind the I Ralph Besler November 30, 1999 Page 2 wails and prevent wetting of the lower level. 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 conteût near optimum. tsackfill placed arouûd 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 thao those exposed. The risk of foundation movement may be greater than indicated in this repCIrt 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 subsurïace 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: SLP IZA,lrso attachment cc: Kurtz and Associates - Attn: Brian Kurtz eåFte*t r0ù t0 to o îrE iEr¡ücs ?rfrßn{ ¡6 5t4 .üi .& .u .o¡ .ola .6rt u;3. sfÀtrDñ¡lD sffi 6Eñi f,r?do .cî1 .tto .t00 .tæ l.1t 2.St ¡[.7] t ¡ie! l¡.0 ¡?,5 tt 2 rdËa bJ DIÀMETER OF PARTICLES Ii{ MILLIMETERS tô 30 t0 ü 7û d¡trlro2 l- t¡J(E to t- ¿,l¿l() É,I¡J6-a0 (' élo U'(î, ô- L'- rù lÀ¡()ËtdfL ¡lo 7ù ð $ !0 eo t00 HtoiðtElEn å{rlYss gEtÊ ¡¡tAL GRADATON TEST RESULTS Fig. 1199 921 HEPWORTH _ PAWLAK GEOTËCHNICAL, INC. g¡Y T0 *1 cß€s GAA!ÉL 73 % LIQUID LIMIT % SAND 22 7t SLTGHTLY SILTY SANDY GRAVEL WITH COBBLES SILT AND CLAY 5 7I PLASTICITY INDEX FROM: BOTTOM OF EXCAVAïON a SAMPLE OF: