HomeMy WebLinkAboutSoils Report 2-22-2011.pdf11.1,
HEPWORTH -PAWLAK GEOTECHNICAL
February 22, 2011
Terrell & Patty Tankersly
do Jack Palomino
815 Blake Avenue
Glenwood Springs, Colorado 81601
Ilepwotth-Pawlak Geotechnical, Inc.
5020 (7,!ounty Road 154
Glenwood Springs. Colorado 81601
Phone: 970-945-7988
Fax: 970-945-8454
Elpgeo@hpgeotech.com
Job No. 111 021A
Subject: Review of Steep Slope, Proposed Addition, Parcel 1, Sitnmons
Subdivision, 2068 County Road 137, Canyon Creek, Garfield County,
Colorado
Dear Mr. & Mrs. Tankersly:
As requested, a representative of Hepworth-Pawlak Geotechnical, Inc. observed the slope
conditions at the subject site on February 20, 2011 to evaluate the slope stability for
construction support. The findings of our observations and recommendations for the
foundation design are presented in this report. We previously conducted a subsoil study
for design of foundations of the existing house at the site and presented our findings in a
report .dated filly 29, 1999, Job No. 199512.
Proposed Construction: The proposed addition will be located on the east side ofthe.
existing house and will be a 20' X 36' one story log structure over a walkout basement
level, similar to the existing residence. The foundation, will be cast -in-place concrete
footings and foundation walls. The southeast corner of the addition (which is about 15%
of the addition footprint) will extend onto the steep slope below the house.
Site Observations: Most of the proposed addition area IS relatively flat with a gentle
slope down to the south-southeast The southeast corner of the addition will be located on
the upper 6 feet of the steep slope down to East Canyon Creek located more than 50 feet
southeast of the addition, The upper 5 feet of the slope in the addition footprint appears
to be t11 material (composed of the on-site rocky soils) up to about 3 to 4 feet thick. The
slope appears to be natural rocky soils below that level. The steep slope has a grade of
about 60% down to the southeast. Vegetation on the overall slope consists of scattered
oak brush and occasional larger pine trees. There is no visible vegetation in the proposed
addition footprint. The flatter part of the addition area had about 1 foot of snow cover
and the steep slope had patchy snow but was mostly bare at the time ofour visit. Many
boulders up to about 4 feet in size are exposed on the steep slope. No evidence of slope
instability, such as ground cracks, distressed vegetation, bulging or erosion was observed.
Conclusions and Recommendations: The existing slope appears stable under current
conditions. Placing the addition on the slope will not significantly adversely impact the
existing natural slope. The fill portion of the slope will be mostly removed by the new
Parker 303-841-7119 6 Colorado Springs 719-63.3-5562 0 Sitverthome 970-468, 1 989
Terrell & Patty Tankersly
February 22, 2011
Page 2
construction. We recommend that the spread footing in the southeast comer of the
addition be deepened so that the outside edge of the footing is set back at least 5 feet
horizontally from the ground surface of the natural slope. The footing elevation should
be extended down until this condition is met. Most of this depth will probably be needed
to provide the required frost cover for the footing. We should observe the excavation
conditions at the time of construction to verify that the setback fromthe slope is met. We
assume that -any new fill on the slope will be supported by the new foundationwalls or
new site retaining walls, separate from the foundation. Fill should be benched into parts
of the slope steeper than 20% and embankment fill should be compacted to at least 95%
of the maximum standard Proctor density at a moisture content near optimum.
Recommendations provided in our previous report should be followed for the new
construction
The recommendations submitted in this letter are based on our observation of the existing
slope conditions and our previous (limited) subsurface exploration at the site. Variations
in the subsurface conditions below the excavation could increase the risk of foundation
movement. We should be advised of any variations encountered in the excavation
conditions for possible changes to recommendations contained in this letter. Our services
donot 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,
HEPWORTH — PAWLAK GEOTCHNICAL, INC.
t1\\aHA II�lIi67/NN�h„r
GC/,
ti
Daniel E. Hardin; ISE. 24443
. %y(,,
Rev. by: SLP o®O@m0omo�w.�°
DEH/ksw
Job No. 111 021A
0
5
is 10
LEGEND:
ti
1
NOTES:
PIT 1
ELEV. = 5716'
=0.
1•
qdeaY
GUEST
HOUSE
1 +4=66
J -200=7
PIT 2 PROFILE PIT
ELEV. = 5708' ELEV. = 5710'
MAIN SEPTIC
RESIDENCE SITE
0
5
10
TOPSOIL; silty sand with gravel, cobbles and boulders, medium dense, slightly moist, brown,
with roots and organics.
GRAVEL, COBBLES, AND BOULDERS (GP—GM); sandy, slightly silty, dense
to very dense, slightly moist, brown, primarily subrounded to roundedrocks
to about 4 or 5 feet in diameter.
Disturbed bulk sample.
Practical digging refusal with backhoe.
1. Exploratory pits were excavated on July 7, 1999 with a backhoe.
2. Locations of exploratory pits were measured approximately by pacing from features on the site
plan provided.
3. Elevations of exploratory pits were approximated by contours on the site plan provided.
Pits logs are drawn to depth.
4. The exploratory pit locations and elevations should be considered accurate only to the degree
implied by the method used.
5. The lines between materials shown on the exploratory pit logs represent the approximate
boundaries between material types and transitions may be gradual.
6. No free water was encountered in the pits at the time of excavating.
Fluctuations in water level may occur with time.
7. Laboratory Testing Results:
+4 = Percent retained an No. 4 sieve
—200 = Percent passing No. 200 sieve
w
0.
199 512
HEPWORTH - PAWLAK
GEOTECHNICAL, INC.
LOGS OF EXPLORATORY PITS
Fig. 2
PASSI e
24 HR. 7 HR
1D 45 MIN. 15 MIN. CO MIN.19 MIN. 4 MIN. 1 N. 1200 /100 N50 130 116 /B /4 3/8'1/2'3/4' 1 1/2' 3' 5'6' - Bp
1
HYDRCME1m ANALYSIS
TIME READINGS
1
U.S. STANDARD SERIES
SIEVE ANALYSIS
CLEAR SQUARE OPENINGS
90
80
70
60
50
40
0
20
10
0
4
.001 .002 .005 .009 .019 .037 .074 .150
10
20
30
.300 .600 1.18 2.36 4.75 9.512.5 19.0 37.5 76.2 1 152 203
DIAMETER OF PARTICLES IN MILLIMETERS
27
, CLAY TO SILT
1 RNE1 MEDIUM (COARSE 1 FINE 0417VEL COARSE I COBBLES
GRAVEL 66
SAND 27 % SILT AND CLAY 7 %
LIQUID LIMIT % PLASTICITY INDEX
SAMPLE OF: Slightly Silty Sandy Gravel FROM: Pit 1 at 7 thru 8 Feet
with Cobbles
40
50
80
70
8D
90
100
20.:MMH•44111W; pi
199 512
HEPWORTH - PAWLAK
GEOTECHNICAL, INC.
GRADATION TEST RESULTS
Fig. 3
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE I
PERCOLATION TEST RESULTS
JOB NO. 199 512
HOLE NO.
HOLE DEPTH
(INCHES)
LENGTH OF
INTERVAL
(MIN)
WATER DEPTH
AT START OF
INTERVAL
(INCHES)
WATER DEPTH
AT END OF
INTERVAL
(INCHES)
DROP IN
WATER
LEVEL
(INCHES)
AVERAGE
PERCOLATION
RATE
(MIN./INCH)
P-1
46
10
9
7 1/2
1 1/2
7 1/2
7
1/2
7
6 1/4
3/4
6 1/4
5 1/2
3/4
5 1/2
4 3/4
3/4
4 3/4
4 1/4
1/2
4 1/4
3 3/4
1/2
3 3/4
3 1/4
1/2
3 1/4
2 3/4
1/2
2 3/4
2 1/4
1/2
2 1/4
1 3/4
1/2
20
P-2
38
10
water added
6 3/4
5 1/2
1 1/4
5 1/2
4 3/4
3/4
4 3/4
4
3/4
4
3 1/2
1/2
3 1/2
3
1/2
7
6
1
6
5 1/2
1/2
5 1/2
5
1/2
5
4 1/2
1/2
4 1/2
4
1/2
4
3 1/2
1/2
20
P-3
52
10
water added
water added
9 1/2
4 3/4
4 3/4
4 3/4
2 1/2
2 1/4
8
5 3/4
2 1/4
5 3/4
3 1/2
2 1/4
3 1/2
1 1/4
2 1/4
8
6 1/2
1 1/2
6 1/2
5
1 1/2
5
3 1/2
1 1/2
3 1/2
2 1/2
1
2 1/2
1
1 1/2
8
NOTE: Percolation holes were hand dug in bottom of shallow backhoe pits and pre-soaked on July 7, 1999. Percolation tests were performed
on July 8, 1999 by H -P Geotech. The average percolation rates were based on the last three readings of each test.