HomeMy WebLinkAboutObservation of Excavation 08.09.2019Kumar & Associates, inc.'
Geotechnical and Materials Engineers
and 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
August 9, 2019
Rick Garnett
P.O. Box 656
Idaho Springs, Colorado 80452
rick(agarnettlaw.net
Subject:
Dear Rick:
44° & Assodat s
3
y gemtwe
www.tumamsa.cam
1489-201
Project No. 19-7-357
Observation of Excavation, Proposed Deck Piers, 8040 County Road 117,
Garfield County, Colorado
As requested, a representative of Kumar and Associates, Inc. observed the excavation at the
subject site on June 12, August 1 and 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 general accordance with our agreement
for professional engineering services to you, dated June 3, 2019. Due to groundwater and
unsuitable soils at design bearing level of 3 feet, multiple trips were needed rather than one.
Twelve deck piers in 10 excavations are proposed. The piers were designed as drilled piers to be
3 feet deep and 12 or 18 -inch diameter bearing on "competent native soil" according to note 7 of
the structural plans.
At the time of our 2 initial visits to the site, excavation for all the piers had not been completed
and several of the excavations were stopped in old fill or clay soil short of reaching the dense
granular soils. When observed on August 8, the pier excavations had been completed to depths
from about 3 to 6 feet below the adjacent ground surface. The soils exposed in the bottom of the
excavations consisted of relatively dense, silty sandy gravel with cobbles. The results of a
gradation analysis performed on a sample of the gravel (minus 3 -inch fraction) obtained from the
site are presented on Figure 1. The laboratory test results are summarized in Table 1. Free water
was encountered in all the pier excavations from roughly 1 to 18 inches deep.
Considering the conditions exposed in the completed excavations and the nature of the proposed
construction, spread footings placed on the undisturbed natural gravel soil designed for an
allowable soil bearing pressure of 2,500 psf should be adequate for support of the proposed deck
piers. The piers should be a minimum diameter of 18 inches. Loose disturbed soils should be
removed from the pier hole bottoms before placing concrete by the tremie method to displace all
the water from the bearing surface. Footings should be provided with adequate soil cover above
Rick Garnett
August 9, 2019
Page 2
their bearing elevations for frost protection. Backfill placed around the pier holes 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 pier hole excavations 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 excavated depth 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
Attachments: Figure 1 ''Gradation ° est Results
Table 1- Summary of Laboratory Test Results
Kumar & Associates, Inc. ® Project No. 19-7-357
1
1
�-e (LMT)\Drofing\1073
10
9
80
70
60
50
40
30
20
10
0
.0
HYDROMETER ANALYSIS
SIEVE ANALYSIS
24 NRS
45 MIN
7 NRS
15 MIN 604IN
TIME READINGS
19MIN 4MIN
1IIN
1290
U
0100 8
5. STANDARD
0 ft0 4
SERIES
0 8
6 11?
CLEAR SQUARE OPENINGS
/6 14 3/8" 3/4^
_—.._—
- 1—
--
1—
— -
. _
1 1/2"
- —
_
.__
6" 8
--
— V
- _—
- -
-
- -
—f-
-
_
_-__
_'
-_
-
. IJ_
-
-
1-
-1
1- -
-
_ 1_
1-
I-
1---
-1--
i
-_.I--:
T
t
r
.---Y_
-T .
+
1
I
-
L -
1
-
1
1
--
01 .002
- 1
1-
.005
1111-
.009
.019
7 1
.037
1-
- 11.1
11-11-1111
- 11--
11 111li1
1
rr11-.
-
17Tlrll
.075 _1 4/1
DIAMETER OF PARTICLES IN MILLIMETERS
0
10
20
30
40
50
80
70
.1 76.2 12700
152
CLAY TO SILT
SAND
GRAVEL
FINE
MEDIUM
COARSE
FINE
COARSE
COBBLES
GRAVEL 65 %
LIQUID LIMIT
SAMPLE OF: Silty Sandy Gravel
SAND 27 %
PLASTICITY INDEX
SILT AND CLAY 8 %
FROM: Bottom of Pier Hole South of
House 8/8/19
0
0
00
PERCENT RETAINED
These test results apply only to the
samples which were tested. The
testing report shall not be reproduced,
except In full, wl houl the wriHen
approval of Kumar & Associates, Inc.
Sieve analysis testing is performed in
accordance with ASTM 06913, ASTM 07928,
ASTM C136 and/or ASTM D1140.
19-7-357
Kumar & Associates
GRADATION TEST RESULTS
Fig. 1
e
47
47
0
® 0)
=W N
m in
C
12 Cn
cp
YL N 2
c O
N C
le CD cv
� W
111
Project No. 19-7.357
SOIL OR
BEDROCK TYPE
Soft, Sandy Silty Clay
Silty Sandy Gravel II
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF
ATTERBERG LIMITS
PLASTIC
INDEX
(%)
LIQUID LIMIT
(%)
PERCENT
PASSING NO.
200 SIEVE
M
VD
00
GRADATION 1
y
N
J
g o
VD
NATURAL
DRY
DENSITY
00
NATURAL
MOISTURE
CONTENT
(%)
kr)
11 SAMPLE LOCATION
BOTTOM OF EXCAVATION
08-01-2019
Close to House
3' Deep
1108-08-2019
South of House