HomeMy WebLinkAboutObservation of Excavation 10.29.18H—Pz-:"z*-_– K 5020 County Road 154
Geotechnical Engineering I Engineering Geology Glenwood Springs, CO 81601
Materials Testing I Environmental Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado
October 29, 2018
Greg Mackey
P.O. Box 398
Basalt, Colorado 81621
maP� cke 33 @,Rmail.com
Project No. 18-7-654
Subject: Observation of Excavation, Proposed Shop/Storage Building, 050 County Road
110, Garfield County, Colorado
Dear Mr. Mackey:
As requested, the undersigned representative of H-P/Kumar observed the excavation at the
subject site on October 24, 2018 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 you, dated October 24, 2018.
The proposed building will be a one tall story steel frame/metal skin structure (50' by 98' in size)
with a slab -on -grade floor. Spread footing foundations were designed for an assumed allowable
soil bearing pressure of 1,500 psf. Borings drilled on a nearby lot, across 110 Road to the
northwest, indicated fine-grained soils are at least 20 feet deep and overlie relatively dense
gravel soils.
At the time of our visit to the site, the foundation excavation had been cut in one level from nil to
6 feet below the adjacent ground surface. The footings were formed and reinforcing steel was
in-place. The soils exposed in the bottom of the excavation consisted of medium stiff, sandy
silty clay and clayey silty sand. Results of swell -consolidation testing performed on samples
taken from the site, shown on Figure 1, indicate the soils have low compressibility under light
loading and have a moderate to high collapse potential (settlement under constant load) when
wetted. The samples were highly compressible under increased loading after wetting. 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 soil designed for an allowable
soil bearing pressure of 1,500 psf can be used for support of the proposed shop/storage building
with a high risk of future settlement. The exposed soils are highly compressible when wetted
and there will likely be some post -constriction settlement of the foundation if the bearing soils
become wet. The settlement could be 2 inches or more, depending on the depth of wetting and
likely cause building distress possible requiring underpinning in the future. It will be critical to
Greg Mackey
October 29, 2018
Page 2
the long-term performance of the building to prevent wetting of the bearing soils from surface
runoff or utility leakage. Roof downspouts should outlet well beyond foundation wall backfill.
The ground surface around the building should be sloped to drain away from the building in all
directions. A swale may be needed on the uphill side to route surface runoff around the building.
Backfill placed around the structure should be compacted and the surface graded to prevent
ponding within at least 10 feet of the building. Landscape that requires irrigation should not be
located within 10 feet of the foundation.
Footings should be a minimum width of 20 inches wide for continuous walls and 3 feet for
columns. Loose and disturbed soils 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 14 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 not be provided.
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.
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,
H -P ` KU MAR
Daniel E. Hardin, P.E.
Rev. by: SLP
DEH/ksw
2(44 4
o z'
E�G\�
attachments Figure 1 — Swell -Consolidation Test Results
Table 1— Summary of Laboratory Test Results
H -P: KUMAR
Project No. 18-7-654
�r
!!1
J
D
U)
W
H
U)
w
0
r Q
LU Ir
Jp
CO CO
H J
LL
O
C�
G
C0
v
LO
m
P4.
ob
0
Z
U
U
O
L
w
0
z
M
U
w
�
�
U
cn
wW
-> Z:
zIrW N
00,E
Z0�
U
UX
U)
LLJ
QZ
J
J
a
c�
LU
ED
LU
f-
Q
D� o
CJ
J
1-
ZZO W
LU
Z N W
W Q Z fA
d
as
Z
Q o
O
U
a
_
�
Q
J
W
�
Q v
d'
J
Q
0
O1
00
QOZ
W
Z 93
J L H
m D FW- o
�c
00
�D
Q 00
O
ZgU
Z
t� b
C"" U
(" U
0
W
o
bd
O2
0�
O 2
O
w
Jtu+'
Z Q
cd U
U y
mQ
U
w
o