HomeMy WebLinkAboutSoils Report.pdfHEPWORTH -PAWLAK GEOTECHNICAL
April 25, 2014
Ty Rice
P.O. Box 398
Carbondale, Colorado 81623
I kr,t.itli I .,i\ l.,i t :t•• i.,
Job No.114 123A
Subject: Subsoil Study for Foundation Design and Percolation Test, Proposed
Residence, 268 Rose Lane, Garfield County, Colorado
Dear Mr. Rice
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 agreement for geotechnical engineering services to
you dated April 18, 2014. The data obtained and our recommendations based on the
proposed construction and subsurface conditions encountered are presented in this report.
Evaluation of potential geologic hazard impacts on the site is beyond the scope of this
study.
Proposed Construction: The proposed residence will be one story wood frame
construction and located on the site as shown on Figure 1. Ground floors are proposed to
be structural above a shallow crawlspace. Cut depths are expected to range between
about 2 to 3 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 in the rear of the property.
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 property was previously occupied with a mobile residence and
numerous outbuildings. At the time of our field exploration, the site had been cleared of
structures except for the pump house and a shed. Outside of disturbed areas, vegetation
consists of grass and weeds with scattered cottonwood trees. The site is located in the
Roaring Fork River valley bottom and the ground surface is relatively flat with a slight
slope down to the west. There is a shallow depression in the center of the site. An
Parker 303-841-7119 • Colorado Spring; 719-033-5562 • Silveri -home 970-40-1989
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existing irrigation ditch crosses the property on the north side. The ditch was dry at the
time of our field exploration.
Subsidence Potential: The Roaring Fork valley in this area is underlain by Pennsylvania
Age Eagle Valley Evaporite bedrock. The evaporite contains gypsum deposits.
Dissolution of the gypsum under certain conditions can cause sinkholes to develop and
can produce areas of localized subsidence. Sinkholes have been observed in nearby
subdivisions during previous work in the area. Sinkholes were not observed in the
immediate area of the subject site. Based on our present knowledge of the site, it cannot
be said for certain that sinkholes will not develop. In our opinion, the risk of ground
subsidence at the property throughout the service life of the residence is low and similar
to other properties in the area but the owner should be aware of the potential for sinkhole
development.
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 I. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about 2 feet of topsoil or fill,
consist of slightly silty sandy gravel with cobbles and small boulders. A one foot thick
clay layer was observed in Pit 1 overlying the granular soil. Results of gradation analyses
performed on samples of sandy gravel with cobbles (minus 5 inch fraction) obtained from
the site are presented on Figure 3. The laboratory test results are summarized in 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 2,500 psf for support of the proposed residence. The natural soils should have
low compressibility and foundation settlement should be less than 1 inch. Footings
should be a minimum width of 16 inches for continuous walls and 2 feet for columns.
Loose and disturbed soils, existing fill and sandy clay encountered at the foundation
bearing level within the excavation should be removed and the footing bearing level
extended down to the undisturbed natural granular 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 10 feet. Foundation
walls acting as retaining structures should be designed to resist a lateral earth pressure
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based on an equivalent fluid unit weight of at least 45 pcf for the on-site granular soil as
backfill. 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 and sandy clay, are suitable to
support lightly loaded slab -on -grade construction. To reduce the effects of some
differential movement, floor slabs (if any) 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.
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 granular soils devoid of vegetation, topsoil and oversized rock.
Underdrain System: Although free water was not encountered during our exploration, it
has been our experience in the area that local perched groundwater can develop during
times of heavy precipitation, seasonal runoff or during irrigation season. Frozen ground
during spring runoff can create a perched condition. We recommend below -grade
construction, such as retaining walls and crawlspace areas, be protected from wetting and
hydrostatic pressure buildup by an underdrain system.
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 drain 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 or drywell. 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.
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
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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 6 inches in the first 10 feet in unpaved
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.
Percolation Testing: A profile pit and three percolation test holes were excavated on
April 18, 2014 at the locations shown on Figure 1. The subsoils exposed in the Profile Pit
consisted of about 11/2 feet of topsoil overlying slightly silty sandy gravel with cobbles
and small boulders to the bottom pit depth of 8 feet. The results of a gradation analysis
performed on a sample of sandy gravel (minus 5 inch fraction) obtained from the Profile
Pit are presented on Figure 3. The sample tested has a USDA Soil Texture Classification
of extremely gravelly sand. No free water or evidence of a 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 April 18, 2014.
Percolation testing was conducted on April 19, 2014 by a representative of Hepworth -
Pawlak Geotechnical, Inc. The percolation rates varied from 6 minutes per inch to 8
minutes per inch with an average of 7 minutes per inch. The percolation test results are
summarized on Table 2. Based on the subsurface conditions encountered and the
percolation test results, the tested area should be suitable for an on-site waste disposal
system. A professional civil engineer should design the 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 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
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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
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.
Louis E. Eller
Reviewed by:
Steven L. Pawlak, P.E.
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attachments Figure 1— Loca C' -b' oratory Pits and Percolation Test Holes
Figure 2 — Logs of Exploratory Pits
Figure 3 - Gradation Test Results
Table 1 — Summary of Laboratory Test Results
Table 2 — Percolation Test Results
cc: Sopris Engineering - Paul Rutledge (prutic�lir
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PIT 1
■
ROSE LANE
PROPOSED
RESIDENCE
268 ROSE LANE
P2
A
PROFILE ■
PIT
LI
A
P3
EXISTING
WELL
0
■
PIT 2
APPROXIMATE SCALE
1"=30'
114 123A
GecPtech
HEPWORTH-PAWLAK GEOTECHNICAL
LOCATION OF EXPLORATORY PITS
AND PERCOLATION TEST HOLES
Figure 1
0
5
10
LEGEND:
ti
_J
PIT 1
P:sr
WC= 29.5
DD= 87
- I +4= 79
- - -200= 4
PIT 2
.P
PROFILE PIT
•
+4= 72
- J -200= 6
FILL; sandy silt and clay, some topsoil, firm, moist, mixed brown and black.
TOPSOIL; organic sandy silt and clay, firm, moist, black.
CLAY (CL); sandy, silty, medium stiff, very moist, brown.
GRAVEL (GM -GP); silty, sandy, with cobbles and boulders, dense, moist, brown, rounded rocks.
2" Diameter hand driven liner sample.
Disturbed bulk sample.
0 _
5
10
NOTES:
1. Exploratory pits were excavated on April 18, 2014 with a Cat 320B trackhoe.
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 (pcf)
+4 = Percent retained on the No. 4 sieve
-200 = Percent passing No. 200 sieve
0)
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114 123A
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HEPWORTH-PAWLAK GEOTECHNICAL
LOGS OF EXPLORATORY PITS
Figure 2
ENT RETAIL It
''ER ENT RETAIN_ it
HYDROMETER ANALYSIS
TIME READINGS
24 HR. 7 HA
45 MIN. 15 MIN. 60MIN19MIN.4 MIN. 1 MIN
0
10
20
30
40
50
60
70
80
90
100
SIEVE ANALYSIS
200
#100
U.S. STANDARD SERIES 1
#50 #30 #16 #8 #4
CLEAR SQUARE OPENINGS
3/8' 3/4' 1 1/2" 3" 5"6"
8°
IW
.091 .002
0� .019 037 .074 .150
CLAY TO SILT
GRAVEL 79 %
1
300 .603 1.19 236 4.75 95125 190 37.5 762 152 203
127
DIAMETER OF PARTICLES IN MILLIMETERS
SAND
GROVEL
FILE I MEDIA (COARSE
SAMPLE OF: Sandy Gravel with Cobbles
SAND 17 %
FEE I COARSE
000OLES
SILT AND CLAY 4 %
FROM: Pit 1 at 3 X to 4 Feet
45'AIN. 15 MIN. 60MIN19MIN.4 MIN. 1 MIN
0
HYDROMETER ANALYSIS
TIME READINGS
10
20
30
40
50
60
70
80
90
100
.001 .002 .005 .009 .019 .037 .074 .150
#200
#100
SIEVE ANALYSIS
U.S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS
#50 #30
#16
#8
#4
3/8'
8'
CLAY TO SI
GRAVEL 72 %
1
90
50
70
60
50
40
20
20
10
100
90
80
70 Z
U
U
60 d
50
r
w
U
40 W
0
30
20
10
0
.300 .600 1.18 2.36 4.75 9.512.519.0 37.5 76.2 121/52 203
DIAMETER OF PARTICLES IN MILLIMETERS
FEE 1 MEDIA (COARSE
SAND 22 %
GROVEL
FINE 1 ODARSE
CCOOLES
SILT AND CLAY 6 %
SAMPLE OF: Sandy Gravel with Cobbles (Extremely FROM: Profile Pit at 4 to 5 Feet
Gravelly Sand)
114 123A
Gaigtech
Hepworth-P4lwlak Geotechnical
GRADATION TEST RESULTS
Figure 3
C rn
3 Sc
> 0
O
r
Orn
0 0
O rn
rn
—Ixn
nnz
r D
r
C t..,
r z
n
VEZI MI 'oN 4oC
ro
b o
II SAMPLE LOCATION
4 to 5
w
Nm
O
A
12
x
N
02
1 87
0 z
3 �jc
r
72
79
GRAVEL
(%)
GRADATION
N
J
° o
0
14_
2 v v
4.12
Q�4n
m 8 y,4
Sandy Clay
UNCONFINED
COMPRESSIVE SOIL OR
STRENGTH BEDROCK TYPE
(PS9
Sandy Gravel with Cobbles 11
{ Sandy Gravel with Cobbles 11
C rn
3 Sc
> 0
O
r
Orn
0 0
O rn
rn
—Ixn
nnz
r D
r
C t..,
r z
n
VEZI MI 'oN 4oC
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 2
PERCOLATION TEST RESULTS
306 NO. 114 123A
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
28
5
Water added
Water added
Water added
Water added
Water added
6
3 3/4
2 1/4
5 3/4
4 1/4
1 1/2
6
5 3/4
4 3/4
1
6 1/4
5
1 1/4
6
5
1
5
4 1/4
3/4
6 1/2
5 1/2
1
5 1/2
4 3/4
3/4
P 2
30
5
Water added
Water added
Water added
Water added
Water added
Water added
6
4 1/2
1 1/2
8
5 1/2
4 1/4
1 1/4
5 1/2
4 1/4
1 1/4
5 3/4
4 3/4
1
5 1/2
4 1/2
1
5 1/2
5
1/2
5
4
1
5 1/2
5
1/2
P 3
28
5
Water added
Water added
Water added
7
4 3/4
2 1/4
7
6 3/4
5
1 3/4
6 3/4
5 1/2
1 1/4
6 3/4
6
3/4
6
4 3/4
1 1/4
Water added
6
5 1/4
3/4
5 1/4
4 1/4
1
4 1/4
3 3/4
1/2
Note: Percolation test holes were hand dug in the bottom of backhoe pits and soaked on April
18, 2014. Percolation tests were conducted on April 19, 2014. The average percolation
rates were based on the last 3 readings of each test.