HomeMy WebLinkAboutObservation of Excavation 09.30.2024
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
September 30, 2024
Steve Spillane
264 Buckthorn Road
New Castle, Colorado 81647
spillanes@hotmail.com
Project No. 24-7-569
Subject: Observation of Excavation, Proposed Bedroom Addition, 4361 Grass Mesa Road,
Garfield County, Colorado
Dear Steve:
As requested, a representative of Kumar & Associates observed the excavation at the subject site
on September 30, 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 general accordance with our agreement for professional engineering
services to you dated September 25, 2024.
The proposed bedroom addition will be built on the southwest corner of the existing residence.
The addition will be a single-story wood-frame structure over a crawlspace. The addition has
been designed to be supported on spread footings sized for an assumed allowable 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 1½
to 2½ feet below the adjacent ground surface. The soils exposed in the bottom of the excavation
consisted primarily of relatively dense, basalt gravel and cobbles in a calcareous sandy silt
matrix. There was foundation backfill within about 4 feet of the existing foundations. The top
of the existing footing was approximately 6 inches below the existing excavation level. We
recommended the foundation backfill be removed from under spread footings and the proposed
foundation be placed on the underlying natural granular soil. The results of a gradation analysis
performed on a sample of sandy silty gravel (minus 3-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.
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 addition.
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 disturbed soils and
existing fill 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
Kumar & Associates