HomeMy WebLinkAboutObservation of Excavation
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
November 3, 2021
Wayne Blotske
34671 Highway 6
Silt, Colorado 81652
(wayne@blotske.net)
Project No. 21-7-788
Subject: Observation of Excavation, Proposed Addition, 34671 Highway 6, East of Silt,
Garfield County, Colorado
Dear Wayne:
As requested, a representative of Kumar & Associates observed the excavation at the subject site
on October 21, 2021 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 you dated October 1, 2021.
The proposed addition will be located on the north side of the existing residence. The garage
area of the addition will be slab-on-grade and the living space will be structural over crawlspace.
Foundations were designed for an assumed allowable soil bearing pressure of 2,500 psf.
At the time of our visit to the site, the foundation excavation had been cut in one level from 2½
to 10 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation
consisted of slightly clayey, sand and silt. Results of swell-consolidation testing performed on
samples taken from the site, shown on Figure 1, indicate the soils are compressible under
conditions of loading and 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 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 20 inches
for continuous walls and 2 feet for columns. Loose 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
protection. Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 12 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. Structural fill placed
Kumar & Associates
Kumar & Associates
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 21-7-788
SAMPLE LOCATION NATURAL
MOISTURE CONTENT
NATURAL
DRY DENSITY
GRADATION
PERCENT PASSING NO. 200 SIEVE
ATTERBERG LIMITS UNCONFINED
COMPRESSIVE STRENGTH SOIL OR BEDROCK TYPE BOTTOM OF THE EXCAVATION
GRAVEL SAND
LIQUID LIMIT PLASTIC INDEX (%) (%)
(%) (pcf) (%) (%) (PSF)
Northeast Corner
HD – 1 4.0 96 63 Slightly Clayey Sand and
Silt
Southwest Corner
HD – 2 6.6 100 52 Slightly Clayey Sand and
Silt