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HEPWORTH-PAWLAK GEOTECHNICAL
March 6, 2015
Crawford Design Build, LLC
Attn: Brad Crawford
P.O. Box 1236
Carbondale, Colorado 81623
(crawforddesienbuild a,comcast.net)
Hepworth-Pawlak Geotechnical, Inc.
5020 County Road 154
Glenwood springs, Colorado 81601
Phone 970-945-7988
Fax 970-945-8454
r , ail hpgco a.hpgcotcch com
Job No.115 035A
Subject: Subsoil Study for Foundation Design and Percolation Test, Proposed
Residence, Lot 18, Callicotte Ranch, 01 10 Sopris Lane, Garfield County,
Colorado
Dear Mr. Crawford:
As requested, Hepworth-Pawlak Geotechnical, Inc. performed a subsoil study and
percolation test for foundation and septic disposal designs at the subject site. The study
was conducted in accordance with our professional services agreement for geotechnical
engineering services to you dated February 4, 2015. The data obtained and our
recommendations based on the proposed construction and subsurface conditions
encountered are presented in this report. Hepworth-Pawlak Geotechnical, Inc. previously
performed a preliminary geotechnical study for Callicotte Ranch and reported our
findings April 19, 2002, Job Number 101 821.
Proposed Construction: The proposed residence will be one story wood frame
construction above a crawlspace and with an attached garage. The residence will located
in the area of the center post shown on Figure 1. Garage floor will be slab -on -grade. Cut
depths are expected to range between about 3 to 4 feet. Foundation loadings for this type
of construction are assumed to be relatively light and typical of the proposed type of
construction. The septic disposal system is proposed to be located downhill and south of
the residence.
If building conditions or foundation loadings are significantly different from those
described above, we should be notified to re-evaluate the recommendations presented in
this report.
Site Conditions: The vacant lot was covered in patchy snow. Vegetation consists of
grass and weeds in the building area with a pinion and juniper forest east and north of the
-2 -
building area. The ground surface is relatively flat with a slight slope down to the
southwest. A shallow abandoned irrigation ditch crosses the upper part of the building
area.
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavating two exploratory pits in the building area and one profile pit in the septic
disposal area at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about one foot of topsoil, consist
of 2 feet of stiff sandy clay overlying basalt gravel with cobbles and silty sandy clay.
Results of swell -consolidation testing performed on relatively undisturbed samples of the
sandy clay, presented on Figures 3 and 4, indicate low compressibility under existing
moisture conditions and light loading and a moderate collapse potential (settlement under
constant load) when wetted. The samples were highly compressible under additional load
after wetting. Results of a gradation analysis performed on samples of gravel and clay
(minus 5 inch fraction) obtained from the site are presented on Figure 5. The laboratory
test results are summarized in Table I. No free water was observed in the pits at the time
of excavation and the soils were slightly moist to moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread
footings placed on the undisturbed natural soil designed for an allowable soil bearing
pressure of 1,500 psf for support of the proposed residence. The soils tend to compress
after wetting and there could be some post -construction foundation settlement if the
bearing soils become wet. Care should be taken to reduce the risk of wetting as described
in the Surface Drainage section of this report. Footings should be a minimum width of
18 inches for continuous walls and 2 feet for columns. Loose and disturbed soils
encountered at the foundation bearing level within the excavation should be removed and
the footing bearing level extended down to the undisturbed natural soils. Exterior
footings should be provided with adequate cover above their bearing elevations for frost
protection. Placement of footings at least 36 inches below the exterior grade is typically
used in this area. 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 be designed to resist a lateral earth
pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as
backfil I. A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly
loaded slab -on -grade construction. To reduce the effects of some differential movement,
floor slabs should be separated from all bearing walls and columns with expansion joints
which allow unrestrained vertical movement. Floor slab control joints should be used to
reduce damage due to shrinkage cracking. The requirements for joint spacing and slab
Job No]15 035A
-4 -
walkway areas. A swale may be needed uphill to direct surface runoff
around the residence.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at
least 10 feet from the building. Consideration should be given to the use
of xeriscape to limit potential wetting of soils below the building caused
by irrigation.
Percolation Testing: A profile pit and three percolation test holes were excavated on
January 12, 2015 at the locations shown on Figure 1. The subsoils exposed in the Profile
Pit below about 11/2 feet of topsoil consist 11/2 feet of stiff sandy clay overlying sandy
gravel and clay with cobbles to the bottom pit depth of 81/2 feet. The results of a gradation
analysis performed on a sample of clayey sand and silt (minus 3/8 inch fraction) obtained
from the site are presented on Figure 6. The sample tested has an USDA Soil Texture
Classification of Loam. No free water or evidence ofa seasonal perched water table was
observed in the pit and the soils were slightly moist to moist. Percolation test holes were
hand dug and soaked with water on January 12, 2015.
Percolation testing was conducted on January 13, 2015, by a representative of Hepworth -
Pawlak Geotechnical, Inc. The percolation rates varied from 20 minutes per inch to 30
minutes per inch with an average of 27 minutes per inch. The percolation test results are
summarized on Table 1. Based on the subsurface conditions encountered and the
percolation test results, the tested area should be suitable for an on-site infiltration waste
disposal system.
Limitations: This study has been conducted in accordance with generally accepted
geotechnical engineering principles and practices in this area at this time. We make no
warranty either express or implied. The conclusions and recommendations submitted in
this report are based upon the data obtained from the exploratory pits excavated at the
locations indicated on Figure 1, the proposed type of construction and our experience in
the area. 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. Our findings include interpolation and extrapolation of the subsurface
conditions identified at the exploratory pits and variations in the subsurface conditions
may not become evident until excavation is performed. If conditions encountered during
construction appear different from those described in this report, we should be notified at
once so re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by our client for design purposes. We
are not responsible for technical interpretations by others of our information. As the
Job No.I 15 035A
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115 035A
H
HEPWORTH-PAWLAK GEOTECHNICAL
LOCATION OF EXPLORATORY PITS
AND PERCOLATION TEST HOLES
Figure 1
Compression
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Moisture Content = 8.7 percent
Dry Density = 80 pcf
Sample of: Sandy Silty Clay
From: Pit 1 at 1 1/2 Feet
Compression
upon
_wetting
0.1
1.0
APPLIED PRESSURE - ksf
10 100
115 035A
HEPWORTH.PAWLAN GEOTECHNICAL
SWELL -CONSOLIDATION TEST RESULTS
Figure 3
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HYDROMETER ANALYSIS I SIEVE ANALYSIS
U 5. STANDARD SERIESI
TIME READINGS 1 CLEAR SOUARE OPENINGS
4Q5HMIN. 15 HA
45 4 MIN 1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8' 3/4" 1 1/7 3' 5'6" 8'
10
20
30
40
50
60
70
80
90
100
.00' 902
L
o. 000
F71 150 -10D JJ} 118 238
DIAMETER OF PARTICLES IN MILLIMETERS
35 125 19.0
375 782 152 203
127
DLAY T:l .LLT
SMD GRAVEL C�DI£S
FINE 1 MEDIUM 1 COAS_ FINE 1 COARSE
GRAVEL 54 %
LIQUID LIMIT %
SAMPLE OF: Slightly Sandy Gravel and Clay
SAND 6 %
SILT AND CLAY 40 %
PLASTICITY INDEX %
FROM: Pit 2 at 4 to 5 Feet
HYDROMETER ANALYSIS
qq TIME READINGS
45 1N.15 MIN. 6OMIN19MIN.4 MIN, 1 MIN. #200
0
10
20
30
40
50
60
70
SIEVE ANALYSIS
U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS
#100 #50
#30 #16 #8 #4
3I8' 3!4" 1 112' 3' 5" 6' 8'
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1
1
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80
70
60
43
30
20
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100
90
80
NT PA INr
CD
70 Z
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60 a
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50 Z
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40 EE
LU
0.
30
80 20
90 10
100 a
.001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2 36 4.75 9.512.519.0 37.5 76.2 12,52 203
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT
GRAVEL 26 %
LIQUID LIMIT %
SAMPLE OF: Sandy Clay with Gravel
SAND
FINE I MEDIUM 1 COHSE
GRAVEL
FINE 1 COARSE
C00aLES
SAND 18 % SILT AND CLAY 56 %
PLASTICITY INDEX %
FROM: Profile Pit at 5 to 5 y Feet
115 035A
I-1
HEPWORTH.PAWLAK GEOTECHNICAL
GRADATION TEST RESULTS
Figure 5
Job No. 115 035A
SUMMARY OF LABORATORY TEST RESULTS
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Sandy Silty Clay II
F Sandy Silty Clay II
USDA - Loam 11
Sandy Clay with Gravel II
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
1 ATTERBERG LIMITS
Y
LAI a -
6 z
LIQUID LIMIT
1
PERCENT
PASSING NO.
200 SIEVE
87
40
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GRADATION
D
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M
18
GRAVEL
(%)
54
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NATURAL
MOISTURE
CONTENT
(%)
N
cc;
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11 SAMPLE LOCATION
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