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HomeMy WebLinkAboutObservation of Excavation 07.12.2024K+AKumar & Associates, Inc.® Geotechnical and Materials Engineers 5020 County Road 154 and Environmental Scientists Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com An Employees Owned Company www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado July 12, 2024 James Gornick Building Specialists Attn: Jim Gornick 1005 Cooper Avenue Glenwood Springs, Colorado 81601 J gornick l 988(&gmail. com Project No. 24-7-406 Subject: Observation of Excavation, Proposed Retaining Wall and Additions, 302 Piiion Drive, Elk Springs, Garfield County, Colorado Dear Jim: As requested, a representative of Kumar & Associates observed the excavation at the subject site on July 12, 2024 to evaluate the soils exposed for foundation support. The findings of our observations and recommendations for the foundation support are presented in this report. The services were performed in accordance with our agreement for professional engineering services to James Gornick Building Specialists dated July 12, 2024. The proposed retaining wall will support a new cut to extend an outdoor patio area. The additions include enclosing a small foundation area that was previously external and supporting a deck extension. The additions and wall have been designed to be supported on spread footings sized for an allowable bearing pressure of 2,000 psf. At the time of our visit to the site, the foundation excavations had been cut in 1 level from 3 to 10 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation below a crushed rock levelling course consisted of dense, basalt cobbles and boulders in a calcareous sandy silt matrix. No free water was encountered in the excavation and the soils were slightly 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 2,000 psf should be adequate for support of the proposed additions and retaining wall. The soils appear dense and post -construction settlement of the foundation should be minor. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Loose 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 also be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 45 pcf for on -site or imported granular soil as backfill. A perimeter foundation drain James Gomick Building Specialists July 12, 2024 Page 2 should be provided to prevent temporary buildup of hydrostatic pressure behind the retaining wall. Structural fill placed within slab -on -grade areas can consist of the on -site minus 6-inch 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 5 feet of the building. Landscape that requires regular heavy irrigation, such as sod, and sprinkler heads should not be located within 5 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, Kumar & Associates, In _Qp,QO �.�. WL P O U161 James H. Parsons, P.E. i&71ts!z4 Rev. by: SLP JHP/kac Kumar & Associates, Inc. 0 Project No. 24-7-406