HomeMy WebLinkAboutObservation of Excavation 7.15.20221(+A 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
July 15, 2022
Yates Construction & Consulting
Attn: Chad Yates
P.O. Box 4793
Aspen, Colorado 81612
chad(cuyatescc.com
Project No. 22-7-439
Subject: Observation of Excavation, Proposed Partial New Foundation and Re -Use of
Existing Foundation For New Residence, 30 Flying Fish Road, Garfield County,
Colorado
Dear Chad:
As requested, the undersigned representative of Kumar & Associates observed the excavation at
the subject site on June 20 and 29, 2022 to evaluate the soils exposed for new 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 June 20, 2022.
The previous residence on this site has been removed and the existing foundation will be used for
support of the new house. Additional new foundations will be placed adjacent to the northeast
portion of the existing foundation. We understand that the old and new foundations will have an
assumed allowable soil bearing pressure of 2,000 psf. The new portion of the house will have a
slab -on -grade in the garage and a small crawlspace area adjacent to the exiting foundation.
We observed the existing foundation on June 20th, which consists of a 4 -foot tall, 8 -inch thick,
concrete stem wall with a 16 -inch -wide footing under it. The foundation appeared to be in good
condition with no evidence of cracking or spalling of the foundation walls and footings. Clay
soils were observed at the crawlspace grade.
We returned to the site on June 291h and observed the excavation for the proposed addition
adjacent to the northeast part of the existing foundation. The excavation was 2t/ to 31/4 feet deep
and the exposed subgrade consisted of mostly clay with some gravel soils exposed in the deeper
part of the excavation. Water was observed on top of the subgrade in the northern part of the
new excavation. A pit dug off the northwest corner of the new part of the excavation showed
about 6 inches of topsoil over clay down to about 3 feet where relatively dense sandy gravel with
cobble soils were encountered down to the bottom of the pit at 4%2 feet.
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. Footings
Yates Construction & Consulting
July 15, 2022
Page 2
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. 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. 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. We assume an interior sump will be installed to control water
in the crawlspace. A perimeter foundation drain could be provided to prevent temporary buildup
of hydrostatic pressure behind the new basement walls and, if constructed should be connected to
the interior sup pump. 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 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,
l
Daniel E. Hardin,I
DEH/kac
cc: Dale Kaup
Kumar & Associates, Inc. ' Project No. 22-7-439