HomeMy WebLinkAboutObservation of Excavation 06.28.2022l GrI *rffi [*i'få"t'tr5'""i ; *' *5t20 Gounty Road 154
Glenwood Springs, Cü 816û1
phone: (S70) 945-7SgB
fax: (97û) S45-8454
email: kagienwoodQ)kumarusa.com
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Jvne28,2022
Red House Architecture
Attn: Bruce Barth
815 Blake Street
Glenwood Springs, Colorado 81601
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Project No.22-7-445
Subject: Observation of Excavation, Proposed Residence, Lot 17, Coryell Ranch,
436 Coryell Ranch Road, Garfield County, Colorado
Gentlemen:
As requested, a representative of Kumar & Associates observed the excavation at the subject site
onJune 23,2022 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 Red House Architecture dated June 21, 2022.
Footings placed on the undisturbed natural river gravel soils and sized for an assumed allowable
bearing pressure of 2,000 psf were designed for the foundation support.
At the time of our visit to the site, the building excavation had been cut in one main level from
ZVzto 3Yzfeetbelow the adjacent ground surface with an interior area stepped down about 2feet.
The soils exposed in the bottom of the excavation consisted ofrelatively dense, silty sandy
gravel and cobbles, just below the upper clay and topsoil in shallower cut areas. The results of a
gradation analysis performed on a sample of the gravel (minus S-inch fraction) obtained from the
site are presented on Figure l. 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 gravel soil designed for an
allowable soil bearing presflro of 2,000 psf should be adequate for support of the proposed
residence. Footings should be a minimum width of 16 inches for continuous walls and2 feet for
columns. Loose and disturbed soils in footing areas shÕuld be removed and the bearing level
extended down to the undisturbed natural soils. Exterior footings should be provided with
adequate soil cover above their bqaring 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 l0 feet. Foundation walls acting as retaining structures should also
be designed to resist alateral earth pressure based on an equivalent fluid unit weight of at least
45 pcf for on-site granular soil as backfill excluding organics and rock larger than 6 inches.
Structural fill placed within floor slab areas can eonsist of the on-site granular soils compacted to
Red House Architecture
June28,2O22
Page2
at least 95oá 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 l0 feet of the building. tandscape that requires regular heavy irrigation, such as sod, and
sprinkler heads should not be located within 5 feet of the foundation.
Coryell Ranch is underlain by Pennsylvania-Age Eagle Valley Evaporite bedrock. The evaporite
contains gypsum deposits. Dissolution of the gypsum under certain conditions can cause
sinkholes to develop and can produce areas of localized subsidence which have been identified in
the Coryell Ranch development. Sinkholes were not observed in the immediate area of the
subject lot but have beeri mapped a few hundred feet east of Lot 17. Based on our present
knowledge of the site, it cannot be said for certain that sinkholes will not develop. In our
opinion, the risk of ground subsidence at Lot 17 throughout the service life of the residence is
low and similar to other lots in the area but the o\ryner should be aware of the potential for
sinkhole development.
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 subsurfbce conditions. trn 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 fuither assistance, please call our office.
Sincerely,
Steven L. Pawlak, P.
SLPlkac
Attachment: Figure 1-
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22-7 -445 Kumar & Associates GRADATION TTST RESULTS Flg. 1