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HomeMy WebLinkAboutObservation of Excavation 02.01.24Kumar & Associates, Inc. K 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 February 1, 2024 Josemia LLC c/o Marcelino Juarez 210 E. Hyman Ave. Ste 101 Aspen, CO 81611 Marcel inoivarez 15 g gmai l . com Project No. 24-7-137 Subject: Observation of Excavation, Proposed Addition, 46374 Highway 6 and 24, Garfield County, Colorado Ladies and Gentlemen: As requested, the undersigned representative of Kumar & Associates observed the excavation at the subject site on January 31, 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 Josemia LLC dated January 31, 2024. We understand the proposed addition has been designed to be founded on spread footings bearing on the natural soils and designed for an allowable soil bearing pressure of 1,500 psf assumed by the structural engineer. At the time of our visit to the site, the foundation excavation had been cut in one level from 4'/2 to 6 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation consisted of relatively dense silty sand and gravel with cobbles and small boulders. A minor depth of 3/-inch screened rock had been placed as a leveling course in some areas. The results of a gradation analysis performed on a sample of the silty sand and gravel with cobbles (minus 5-inch fraction) obtained from the site are presented on Figure 1. 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 addition. The exposed soils tend to compress when wetted and there could be some post -construction settlement of the foundation differential to the existing residence, especially if the bearing soils become wet. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for columns. Loose and disturbed soils and existing fill 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 protection. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by Josemia LLC February 1, 2024 Page 2 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 50 pcf for on -site soil as backfill. A perimeter foundation drain should be provided to prevent temporary buildup of hydrostatic pressure behind the basement walls and prevent wetting of the lower level. Structural fill placed within floor slab 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. 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 & Assoc Robert L. Duran. Rev. by: DEH RLD/kac Attachment: Figure 1 — Gradation Test Results Kumar & Associates, Inc. 0 Project No. 24-7-137