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HEPWORTH-PAWLAK GEOTECHNICAL
April 30, 2015
Blu Homes
Attn: Tyler Toohey
1245 Nimitz Avenue
Vallejo, California 94592
(tyler.toohey@ bluhomes.com)
Hepworth-Pawlak Geotechnical, Inc.
5020 County Road 154
Glenwood Springs, Colorado 81601
Phone: 970-945-7988
Fax: 970-945-8454
email: hpgeo@hpgeotech.com
Job No.1 15 144A
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 15, Stirling
Ranch, 657 Schooner Lane, Missouri Heights, Garfield County, Colorado
Dear Mr. Toohey:
As requested, Hepworth-Pawlak Geotechnical, Inc. performed a subsoil study for design
of foundations at the subject site. The study was conducted in accordance with our
proposal for geotechnical engineering services to Blu Homes dated March 20, 2015. The
data obtained and our recommendations based on the proposed construction and
subsurface conditions encountered are presented in this report. We previously performed
a subsoil study for a house on this lot as described in a report dated February 19, 2004,
Job No. 104 142.
Proposed Construction: The proposed residence will be a one story modular structure
over a crawlspace with an attached garage. The garage floor will be slab -on -grade. Cut
depths are expected to range between about 3 to 5 feet. Foundation loadings for this type
of construction are assumed to be relatively light and typical of the proposed type of
construction.
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 site was vacant and free of snow at the time of our field
exploration. The ground surface in the building area is relatively flat with gentle slopes
down to the northeast and southwest. Vegetation consists of sage brush with scattered
Parker 303-841-7119 • Colorado Springs 719-633-5562 • Silverthome 970-468-1989
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pinon trees and an understory of grass and weeds. Basalt cobbles and boulders were
observed on the ground surface to the east and west of the house location.
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavating two exploratory pits at the approximate locations shown on Figure 1. The
logs of the pits are presented on Figure 2. The subsoils encountered, below about 11/2 to 2
feet of topsoil, consist of 4 to 61 feet of stiff sandy silt and clay overlying basalt rocks up
to boulder size in a sandy clay matrix. Results of swell -consolidation testing performed
on relatively undisturbed samples of the sandy silt and clay, presented on Figure 3,
indicate low compressibility under existing moisture conditions and light loading and a
low collapse potential (settlement under constant load) when wetted. The samples were
moderately to highly compressible under increased loading after wetting. Results of a
gradation analysis performed on a sample of gravelly sandy silt and clay (minus 3 inch
fraction) obtained from the site are presented on Figure 4. The laboratory test results are
summarized on Table 1. 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 on the order of 1 to 11 inches of post -construction
foundation settlement. Footings should be a minimum width of 18 inches for continuous
walls and 2 feet for columns. Loose and disturbed soils and existing topsoil 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 backfill.
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
reinforcement should be established by the designer based on experience and the intended
slab use. A minimum 4 inch layer of free -draining gravel should be placed beneath slabs.
Job No. 115 I44A
'-'Piech
3 -
This material should consist of minus 2 inch aggregate with less than 50% passing the
No. 4 sieve and less than 2% passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95% of
maximum standard Proctor density at a moisture content near optimum. Required fill can
consist of the on-site soils or imported granular soils devoid of vegetation, topsoil and
oversized rock.
Underdrain System: AIthough free water was not encountered during our exploration, it
has been our experience in this area that local perched groundwater can develop during
times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can
also create a perched condition. We recommend below -grade construction, such as
retaining walls and deep crawlspace areas, be protected from wetting and hydrostatic
pressure buildup by an underdrain system. Shallow crawlspaces (less than 4 feet) should
not needan underdrain system provided that the ground surface around the house slopes
away as described in the Surface Drainage section of this report.
If installed, the drains should consist of drainpipe placed in the bottom of the wall backfill
surrounded above the invert level with free -draining granular material. The drains should
be placed at each level of excavation and at least 1 foot below lowest adjacent finish
grade and sloped at a minimum 1% to a suitable gravity outlet. Free -draining granular
material used in the underdrain system should contain less than 2% passing the No. 200
sieve, less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The
drain gravel backfill should be at least 11/2 feet deep. An impervious membrane such as a
30 mil PVC liner should be placed below the drain gravel in a trough shape and attached
to the foundation wall to prevent wetting of the bearing soils.
Surface Drainage: The following drainage precautions should be observed during
construction and maintained at all times after the residence has been completed:
1) Inundation of the foundation excavations and underslab areas should be
avoided during construction.
2) Exterior backfill should be adjusted to near optimum moisture and
compacted to at least 95% of the maximum standard Proctor density in
pavement and slab areas and to at least 90% of the maximum standard
Proctor density in landscape areas. Free -draining wall backfill should be
capped with about 2 feet of the on-site, finer graded soils to reduce surface
water infiltration.
3) The ground surface surrounding the exterior of the building should be
sloped to drain away from the foundation in all directions. We
recommend a minimum slope of 12 inches in the first 10 feet in unpaved
• Job No. 115 144A
GecPtech
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areas and a minimum slope of 3 inches in the first 10 feet in pavement and
walkway areas.
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 foundation caused
by irrigation.
Percolation Testing: Percolation tests were conducted on April 15, 2015 to evaluate the
feasibility of an infiltration septic disposal system at the site. One profile pit and three
percolation holes were dug at the locations shown on Figure 1. The test holes (nominal
12 inch diameter by 12 inch deep) were hand dug at the bottom of shallow backhoe pits
and were soaked with water one day prior to testing. The soils exposed in the percolation
holes are similar to those exposed in the Profile Pit shown on Figure 2 and consist of
about 2 feet of topsoil and 3 feet of USDA Soil Classification silty clay loam overlying
basalt rocks in a sandy silt and clay matrix. A USDA gradation was performed on a
sample from the Profile Pit and the test results are shown on Figure 5.
The percolation test results are presented in Table 2. Based on the subsurface conditions
encountered and the percolation test results, the tested area should be suitable for a
conventional infiltration septic disposal system. A civil engineer should design the
infiltration septic 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 I and to the depths shown on Figure 2, 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.
Job No. 115 144A
GeStech
-5
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
project evolves, we should provide continued consultation and field services during
construction to review and monitor the implementation of our recommendations, and to
verify that the recommendations have been appropriately interpreted. Significant design
changes may require additional analysis or modifications to the recommendations
presented herein. We recommend on-site observation of excavations and foundation
bearing strata and testing of structural fill by a representative of the geotechnical
engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
Daniel E. Hardin, P.E. 4 2 3.
eke
vit i,`24
Reviewed by:
Steven L Pawlak, P.E.
DEH/ljf
Attachments: Figure 1 — Location of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
Figure 3 — Swell -Consolidation Test Results
Figure 4 — Gradation Test Results
Figure 5 — USDA Gradation Test Results
Table 1 — Summary of Laboratory Test Results
Table 2 — Percolation Test Results
Job No. 115 144A
C---1(r)tech
PERC 2
A
PERC 3 /
A //
/ •
/ PROFILE PIT
LOT 15
STIRLING RANCH
115 144A
HEPWORTH-PAWLAK GEOTECHNICAL
TO SCHOONER LANE
PERC 1
A
APPROXIMATE SCALE
1"=20'
LOCATION OF EXPLORATORY PITS
Figure 1
a
5
10
LEGEND:
6.1
- -
NOTES:
PIT 1
WC=13.8
DD=82
-200=68
_ _ WC=10.8
+4=22
-200=47
PIT 2
PROFILE PIT
r
_ _ GRAVEL=1
SAND=16
SILT=51
CLAY=32
TOPSOIL; silty, sandy, clay, organic, medium stiff, moist, dark brown.
SILT AND CLAY (ML -CL); sandy, gravelly, stiff, moist, light brown, calcareous.
BASALT FRAGMENTS (GC); up to boulder size in sandy clay matrix, about 70% greater than 3" in size,
calcareous, dense, slightly moist, light brown.
2" Diameter hand driven liner sample.
Disturbed bulk sample.
0
5
10
1. Exploratory pits were excavated on April 14, 2015 with a JD 35 mini -excavator.
2. Locations of exploratory pits were measured approximately by pacing from features shown on the site plan
provided.
3. Elevations of exploratory pits were not measured and the logs of exploratory pits 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. Fluctuation in water level may occur with time.
7. Laboratory Testing Results:
WC = Water Content (%)
DD = Dry Density (pct)
+4 = Percent retained on the No. 4 sieve
-200 = Percent passing No. 200 sieve
Gravel = Percent retained on No. 10 Sieve
Sand = Percent passing No. 10 sieve and retained on No. 325 sieve
Silt = Percent passing No. 325 sieve to particle size .002mm
Clay = Percent smaller than particle size .002mm
Depth - Feet
Compression %
Compression %
0
1
2
3
4
5
6
Moisture Content = 13.8 percent
Dry Density = 82 pcf
Sample of: Sandy Silt and Clay
From: Pit 1 at 3 Feet
7
0.1
0
1
2
3
4
5
'''''''''N"\ Compression
upon
wetting
1.0 10
APPLIED PRESSURE - ksf
100
Moisture Content = 9.4 percent
Dry Density = 100 pcf
Sample of: Sandy Silt and Clay
From: Pit 2 at 2 Feet
--------------,...__-d
Compression
upon
wetting
0.1
1.0 10
APPLIED PRESSURE - ksf
100
115 144A
H EPWORTH-PAWLAK GEOTECHNICAL
SWELL -CONSOLIDATION TEST RESULTS
Figure 3
NT RET • ► 1
HYDROMETER ANALYSIS I SIEVE ANALYSIS
24R. 7 HR TIME READINGS U.S. STANDARD SERIES1 CLEAR SQUARE OPENINGS
0 45 MIN. 15 MIN. 60MIN19MIN.4 MIN. 1 MIN. #200 #100 #50 #30 #16 #8 #4 3/8" 3/4' 1 1/2" 3" 5"6' 8" 100
10
20
30
40
50
60
70
80
90
1
J
1
90
80
70
60
50
40
30
20
10
100 C - 0
.001 .002 .005 .009 .019 .037 .074 .150 .300 .600 1.18 2.36 4.75 9.5 19.0 37.5 76.2 152 203
12.5 127
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT
SAND
GRAVEL
FINE
1 MEDIUM 1 COARSE
FINE 1 COARSE
COBBLES
GRAVEL 22 %
LIQUID LIMIT %
SAMPLE OF: Gravelly, Sandy, Silt and Clay
SAND 31 %
PLASTICITY INDEX
SILT AND CLAY 47 %
0/0
FROM: Pit 1 at 5 Feet
• ' NT P• ►ei
" " ENT RET.I t
HYGROMETER ANALYSIS
24 H�� 7 HR TIME READINGS 1 MIN.
0 45 MIN. 15 MIN. 60MIN19MIN.4 MIN. #325
10
20
30
40
50
60
70
80
90
100
.0 1 .002 .005 .009 .019
SIEVE ANALYSIS
U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS
#140 #60 #35 #18 #10 #4
3/8" 3/4 11/2' 3° 5'6" 8" 100
90
80
1
1
1
1
1
.045 .106 .025 .500 1.00 2.00 4.75 9.5
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY
SILT
SAND
V. FINE 1 FINE I MEDIUM !COARSE N. COARSE
GRAVEL 1 % SAND 16 %
USDA SOIL TYPE: Silty Clay Loam
70
60
50
40
30
20
10
0
19.0 37.5 76.2 152 203
GRAVEL
SMALL 1 MEDIUM 1 LARGE
SILT 51 %
COBBLES
CLAY 32 %
FROM: Pit 3 at 3 Feet
g at m
115144A
Hepworth—Pawlak Geotechnical
USDA GRADATION TEST RESULTS
Figure 5
Job No. 115 144A
SOIL OR
BEDROCK TYPE
Sandy Silt & Clay
Gravelly Sandy Silt & Clay 11
Sandy Silt & Clay 11
Silty Clay Loam 11
cv
M
4c
17
PERCENT
PASSING
NO. 200
SIEVE
00
CD
47
GRADATION
0
0
O
GRAVEL
(%)
N
N
r'
NATURAL
DRY
DENSITY
(pcf)
N
O
Q
O
v—
NATURAL
MOISTURE
CONTENT
(%)
13.8
10.8
d'
O
SAMPLE LOCATION
PIT DEPTH
(ft)
1 3
5
N
CO
N
11 Profile
z
O
1'
U
(0
J
U
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 2
PERCOLATION TEST RESULTS
JOB NO. 115 144A
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
44
10
Water added
9
61/2
21/2
10
6%
5'%
1
5'/
41/2
1
8%
7'/
1
7'%
6'/
1
61/2
5%
1
P-2
52
10
Water added
8
5%
21/2
10
51/2
4%2
1
4'/
3
11/2
8
61/2
1'%
6'/z
5'/
1
51/2
4%2
1
41/2
31/2
1
P-3
55
10
Water added
Water added
81/2
51/2
3
5
51/2
31/2
2
3%
1'/
2
111/2
81/2
3
8'/
6
2'/2
6
41/2
11/2
41/2
21/2
2
111/2
8
3%
8
6
2
6
4%
11/2
Note: Percolation test holes were hand dug in the bottom of backhoe pits and soaked
on April 14, 2015. Percolation tests were conducted on April 15, 2015. The
average percolation rates were based on the last three readings of each test.