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HomeMy WebLinkAboutObservation of Excavation 11.02.17H-PVKUMAR Gaotecùnlcal Englneedng I Engineering Geology Matedals Tasöng I Envircnmantal 5020 County Road 154 Glenwood Springs, C0 81601 Phone: (970) 94S7988 Fax (970) 94s8454 Email: hpkglenwood@kumarusa.@m Office Locations: Denver {HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado November 2,2017 Wood Doctor Construction, Inc. Attn: Bruce Hasselbring 300 Oak Run Road Carbondale, Colorado 81623 bruceh@sonris.net Project No. 17-7-788 Subject: Observation of Excavation, Proposed Detached Garage, Lot 45, Panorama Ranches,0196 Sunlight Drive, Missouri Heights, Garfield County, Colorado Dear Mr. Hasselbring: As requested, a representative of H-P/Ifumar observed the excavation at the subject site on October 30,2017 to evaluate the soils exposed for foundation support. The findings of our observations and recommendations 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 October 25,2017. The proposed detached garage will be a one story wood frame structure with a slab-on-grade floor. It appears that the north and east sides of the garage will have 3 to 4 foot high retaining walls. Foundations were designed for an assumed allowable soil bearing pressure of 2,000 psf. At the time of our visit to the site, the foundation excavation had been cut in three levels from ZYz to 4Vzfeet below the adjacent ground surface. The soils exposed in the bottom of the excavation consisted of medium stiff to stiff, sandy silty clay. Results of swell-consolidation testing performed on a sample taken from the site, shown on Figure l, indicate the soils are slightly compressible under light loading with a low collapse potential when wetted under light loading. The sample was moderately to highly compressible under 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 soil designed for an allowable soil bearing pressure of 1,500 psf can be used for support of the proposed garage. The exposed soils tend to compress when wetted and there could be post-construction settlement of the foundation if the bearing soils become wet. Footings should be a minimum width of 16 inches for continuous walls and2fæt for columns. l,oose and disturbed soils in footing areas should be removed and the bearing 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 Wood Doctor Construction, Inc. November 2,2017 Page2 protection. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12feet. Foundation walls acting as retaining structures 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. A perimeter foundation drain should be provided to prevent temporary buildup of hydrostatic pressure behind the foundation retaining walls and prevent wetting of the garage level. An impervious membrane, such as 20 mil PVC should be provided below the drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils. Structural fill placed within floor slab areas can consist of the on-site soils compacted to at least 95Vo 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, H-P*KUMAR <. Daniel E. Hardin, Rev by: SLP DEHlkac attachment Figure I - Swell-Consolidation Test Results cc: MikeThele,StructuralEngineer(mike@mikethelepe.com) H.P*KUTVIAR Project No. 17-7-788 I a ! ÊI ð ã Ê SAMPLE OF: Sondy Silty Cloy FROM: Footing Grode neor SE Cornerof Goroge WC = 6.4 %, DÐ = 97 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I L \ I ) rn.!. Elt faluú oppry dry to tÈ Empld t.¡bd, ftc tc{ng ßpd ùoll mt b. rædæd, dcèpl iîld, rilhd th rdttcn cpdol ol(mø od ¡!ed.¡. lñ. Sr!$:ødildbn kll¡ôg Ëdomd in rccddons rü m D-41ı. 1 JJ L¡l =t¡, I zotr Õ =o anz.oo 0 -1 -2 -3 -4 -5 -b -7 1.0 r00 17 -7 -788 H-PryKUMAR SWELL_CONSOLIDATION TEST RTSULTS 1Fig.