HomeMy WebLinkAboutObservation of Excavation 11.11.2019I
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and Fnwlronenarllal Srlentisin
5020 County Road 154
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
November 11, 2019
Great Lakes Construction
Attn: Chris Lake
P.O. Box 313
New Castle, Colorado 81647
t;l cchris 1 @gmail. coin
Subject:
Gentlemen:
RECEIVED
ULt.. U V ,CUL
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
Project No. 19-7-679
Observation of Excavation, Proposed Retaining Wall, 115 Chaparral Circle,
Glenwood Springs, Colorado
As requested, a representative of Kumar & Associates, Inc. observed the excavation at the
subject site on November 8, 2019 to evaluate the soils exposed for foundation support. The
findings of our observations and recommendations for the foundation design are presented in this
report. The services were performed in accordance with our agreement for professional
engineering services to Great Lakes Construction, dated November 7, 2019.
The retaining wall design is reinforced concrete construction supported on a continuous spread
footing sized for an allowable bearing pressure of 2,000 psf with a width of 3 to 4 feet. An
equivalent fluid, lateral earth pressure of 40 pcf was assumed behind the wall.
At the time of our visit to the site, the wall had been constructed and the excavation had been cut
in one level from 2% to 5 feet below the adjacent ground surface. The soils exposed in the
bottom of the excavation consisted of stiff, sandy silty clay with scattered gravel. Results of
swell -consolidation testing performed on a sample taken from the site, shown on Figure 1,
indicate the soils have low to moderate compressibility under conditions of loading and wetting.
No free water was encountered in the excavation and the soils were moist and not frozen.
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 should be adequate for support of the proposed retaining wall.
The exposed soils tend to compress when wetted and there could be some post -construction
movement mainly if the bearing soils become wet. The footing should be provided with
adequate soil cover above its bearing elevation for frost protection. The retaining walls can be
designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 40
pcf for imported granular soil such as road base as backfill. A perimeter foundation drain should
be provided to prevent temporary buildup of hydrostatic pressure behind the wall. Backfill
Great Lakes Construction
November 11, 2019
Page 2
placed behind the structure should be compacted to at least 90% of standard Proctor density and
the surface graded to possess a positive slope away from the wall.
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.
If you have any questions or need further assistance, please call our office.
Sincerely,
Kumar & Associates, Inc.
Steven L. Pawlak,
SLP/kac
Attachment: Figure 1 - nsolidation Test Results
Kumar & Associates, Inc. 0 Project No. 19.7.679
1
CONSOLIDATION
—2
SAMPLE OF: Sandy Silty Clay
FROM: Bottom of Excavation 11/8/19
WC = 16.2 %, DD = 106 pcf
—200 = 71
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'New and heseclslei, he Swell
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I ADDITIONAL COMPRESSION
�I UNDER CONSTANT PRESSURE
1 DUE TO WETTING
1.0
19-7-679 Kumar & Associates
APPLIED PRESSURE - KSF 10 100
SWELL—CONSOLIDATION TEST RESULT
Fig. 1