HomeMy WebLinkAboutObservation of Excavation 10.25.24
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
October 25, 2024
Inter-Mountain Engineering
Attn: Jeff Spanel
30 Benchmark Road, Suite 216
Avon, Colorado 81620
jspanel@inter-mtn.net Project No. 24-7-541
Subject: Observation of Excavation, Proposed Mud Room Addition, 190 Piedmont Road,
Garfield County, Colorado
Dear Jeff:
As requested, a representative of Kumar & Associates observed the excavation at the subject site
on October 1, 2 and 14, 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 Inter-Mountain Engineering dated September 12, 2024.
The proposed mud room will be built on the northwest side of the existing residence. The
addition has been designed to be supported on spread footings sized for an allowable bearing
pressure of 2,000 psf.
At the time of our October 1 visit to the site, the foundation excavation had been cut to one level
approximately ½ foot below the adjacent ground surface. The soils exposed in the bottom of the
excavation consisted of topsoil. We recommended removing the topsoil to expose the
underlying natural soils. At the time of our October 2 visit to the site, the foundation excavation
had been cut to one level from 2½ to 5½ feet below the adjacent ground surface. The soils
exposed at the bottom of the excavation consisted of silty sand to sandy silt with scattered gravel
in the southeastern part of the excavation and sandy clay in the rest of the excavation. We
recommended that the clay soils exposed in the excavation be removed down to the sandy silt
with scattered gravel. At the time of our October 14 visit to the site, the foundation excavation
was cut to one level between 3½ and 6 feet below the adjacent ground surface and to expose the
bottom of the existing footing. The soil exposed in the bottom of the excavation consisted of
relatively stiff/dense sandy silt to silty sand with scattered gravel. Results of swell-consolidation
testing performed on a sample of the sandy silt 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.
Inter-Mountain Engineering
October 21, 2024
Page 2
Kumar & Associates, Inc. ® Project No. 24-7-541
The sub-excavated depth was backfilled with structural fill consisting of imported CDOT Class 6
base course moisture conditioned to near optimum and compacted to at least 98 percent of the
maximum standard Proctor density. We performed compaction testing on the structural fill to
confirm adequate compaction. The results of the compaction testing are attached to this report.
Considering the conditions exposed in the excavation the results of compaction testing for the
structural fill and the nature of the proposed construction, spread footings placed on the natural
soils or compacted structural fill designed for an allowable soil bearing pressure of 2,000 psf can
be used for support of the proposed addition. The native soils tend to compress when wetted and
there could be some post-construction settlement of the foundation if the bearing soils become
wet. The settlement could be differential to the existing residence and that should be considered
in the design. Footings should be a minimum width of 16 inches for continuous walls and 2 feet
for columns. 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 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. 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.
Kumar & Associates