HomeMy WebLinkAboutObservation of Excavation 10.4.22'(+AKumar ni Associateinc.
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 Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
October 4, 2022
Gruenefeldt Construction
Attn: Dan Gruenefeldt
P.O. Box 1910
Basalt, Colorado 81621
dan(& gruenefeldt. com
Project No. 22-7-670
Subject: Observation of Excavation, Proposed Residence, Lot M41, Aspen Glen
Subdivision, 21 Tellico Court, Garfield County, Colorado
Dear Dan:
As requested, the undersigned representative of Kumar & Associates observed the excavation at
the subject site on October 3, 2022 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 3, 2022. We previously provided a subsoil study for
design of a residence on this property dated November 29, 2018, Project No. 18-7-630.
The proposed residence will be a one-story wood frame structure with a slab -on -grade floor.
Foundations were designed for an allowable soil bearing pressure of 2,000 psf.
At the time of our visit to the site, the foundation excavation had been cut in one level from 2 to
3'/2 feet below the adjacent ground surface. The soils exposed in the bottom of the excavation
consisted of stiff, sandy silty clay. No free water was encountered in the excavation and the soils
were moist. Recent rain had resulted in some saturation of the subgrade soils on the east side of
the excavation. Subsequent foot traffic had resulted in disturbance of the subgrade soils.
Workers were in the process of redirecting drain water away from the footing area and the
disturbed soils will be removed prior to forming footings. Footings on the west side of the
excavation were being formed.
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 can be used for support of the proposed residence. 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 16 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 10 feet.
Gruenefeldt Construction
October 4, 2022
Page 2
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 not be needed for the proposed slab on grade lower floor
construction. Structural fill placed within floor slab areas will consist of the imported 3/ -inch
road base 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.
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,
Daniel E
DEH/kac
Kumar & Associates, Inc. Project No. 22-7-670