HomeMy WebLinkAboutObservation of Excavation 06.20.2019K+A
Kumar & Associates, l c.
Geatethr's,al and Materials Engineers
end Environmental Scientists
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
June 20, 2019
Kuersten Construction
Attn: John Kuersten
P.O. Box 1530
Rifle, Colorado 81650
ohn cukwnt•"ci , • ^ i on.coin
Subject:
Dear John:
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30.
Project No. 19-7-382
Observation of Excavation, Proposed Shop, 4520 County Road 214 (Peach Valley
Road), Garfield County, Colorado
As requested, a representative of Kumar & Associates, Inc. observed the excavation at the
subject site on June 17, 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 Kuersten Construction, dated June 17, 2019.
The proposed shop will be a one-story wood frame structure, 40' by 50', with a slab -on -grade
floor. Foundations were designed based on an assumed allowable soil bearing pressure of
1,500 psf.
At the time of our visit to the site, the foundation excavation had been cut in two levels from 21/2
to 10 feet below the adjacent ground surface. The step in grade between levels was 11A feet
down to the south. The soils exposed in the bottom of the excavation consisted primarily of
medium stiff, sandy silty clay. Weathered shale bedrock was exposed in the northwest, deepest
corner of the excavation. Results of swell -consolidation testing performed on samples of the
sandy silty clay taken from the site, shown on Figures 1 and 2, indicate the soils are moderately
compressible under conditions of loading and wetting. No free water was encountered in the
excavation and the soils were moist.
Based on our initial observations and the apparent compressibility of the clay soils versus the
incompressible shale bedrock, we recommended that at least 2 feet of the clay soils be removed
from below footing grade and be replaced with structural fill consisting of imported %-inch road
base. The road base should be compacted to at least 98% of the maximum standard Proctor
density at a moisture content near optimum and extend at least 1 foot beyond the footing edge.
Considering the conditions exposed in the excavation and the nature of the proposed
construction, spread footings placed on the undisturbed natural bedrock or at least 2 feet of
structural fill in the clay soil area designed for an allowable soil bearing pressure of 1,500 psf can
be used for support of the proposed shop. The clay soils tend to compress under loading and
there could be some post -construction settlement of the foundation on the order ofY2 to 1 inch.
Footings should be a minimum width of 18 inches for continuous walls and 2 feet for columns.
Kuersten Construction
June 20, 2019
Page 2
Loose and disturbed soils in footing areas should be removed and the bearing level extended
down to the undisturbed bedrock or structural fill. 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. A perimeter foundation drain should be provided to prevent
temporary buildup of hydrostatic pressure behind retaining portions of the foundation walls and
prevent wetting of the lower level. Structural fill placed within floor slab areas can consist of
imported granular 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.
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,
Kumar & Associates, Inc.
cf
Daniel E. Hardin, P. t 0 24443 z.
Rev. by: SLP gi'• 1:jYlj�� •'4 4
DEH/kac
attachments Figures 1 and 2 — Swell -Consolidation Test Results
cc: Glenwood Structural & Civil, Inc. — Adolfo Gorra (gsciasopris_ ix_I)
Kumar & Associates, Inc.
Project No. 19-7-382
F_1p3Z197392-0
CONSOLIDATION - SWELL
1
0
-1
— 2
— 3
— 4
— 5
— 6
,new t x ...,w* oh* a.a a h.
. im*. t..ted Tho tret4 report
. nW/ not a rep , .amt an
fWt. without 11* wntt.n oppro.ot el
Nvn or cog M..eeiet... he. $.ell
Can.ataMn Intim partmww7 in
euordoew. with Ana D-454.
SAMPLE OF: Sandy Silty Clay
FROM: Footing Grade North Side
WC = 16.9 %, DD = 108 pcf
NO MOVEMENT UPON
WETT1 NG
19-7-382
f
1.0 APPLIED PRESSURE — K$F fD 400
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULT
Fig. 1
CONSOLIDATION - SWELL
-10
SAMPLE OF: Sandy Silty Clay
FROM: Footing Grade Southeast Corner
WC = 17.1 %, DD = 104 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
ib... teal nvuh, tippy a"% to tn•
N mart
ah▪ em not Wird.+ nproduct.& unapt In
fWl..IlhaulIhe.r$ti.n opproroi opoof
%ammo, and Abrader.. InC SY.9
pen.eedellon I101.6 pMofln.tl In
e aeefdonu o?tl ASN D-4646.
1.0 APPLIED PRESSURE - KSF 10 100
19-7-382
Kumar & Associates
SWELL -CONSOLIDATION TEST RESULT
Fig. 2