HomeMy WebLinkAboutSoils Report 04.28.2016SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 4, NATIVE SPRINGS
GARFIELD COUNTY, COLORADO
JOB NO. 116 098A
APRIL 28, 2016
PREPARED FOR:
DENA CLOUSE
120 WEST 4t1' STREET
RIFLE, COLORADO 81650
(celdena @ gmail.cona)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS - 4 -
FOUNDATION AND RETAINING WALLS - 5 -
FLOOR SLABS - 5 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 6 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 AND 5 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located at
Lot 4, Native Springs, Garfield County, Colorado. The project site is shown on Figure 1.
The purpose of the study was to develop recommendations for the foundation design.
The study was conducted in accordance with our agreement for geotechnical engineering
services to Dena Clouse dated April 5, 2016. Hepworth-Pawlak Geotechnical, Inc.
previously performed a preliminary geotechnical study for Native Springs subdivision
development and reported our findings January 16, 2001, Job No. 100 460.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obtained during the
field exploration were tested in the laboratory to determine their classification,
compressibility or swell and other engineering characteristics. The results of the field
exploration and laboratory testing were analyzed to develop recommendations for
foundation types, depths and allowable pressures for the proposed building foundation.
This report summarizes the data obtained during this study and presents our conclusions,
design recommendations and other geotechnical engineering considerations based on the
proposed construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The proposed residence will be two story wood frame construction above a crawlspace
and with an attached two story garage. Garage floor will be slab -on -grade. Grading for
the structure is assumed to be relatively minor with cut depths between about 2 to 4 feet.
We assume relatively light foundation loadings, typical of the proposed type of
construction.
If building loadings, location or grading plans change significantly from those described
above, we should be notified to re-evaluate the recommendations contained in this report.
Job No. 116 098A
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2
SITE CONDITIONS
The lot is being used as fenced irrigated horse pasture and vegetated with grass and
weeds. The ground surface is relatively flat and slopes down to the southwest at a grade
of about 2 percent.
FIELD EXPLORATION
The field exploration for the project was conducted on April 8, 2016. Two exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface
conditions. The borings were advanced with 4 inch diameter continuous flight augers
powered by a truck -mounted CME -45B drill rig. The borings were logged by a
representative of Hepworth-Pawlak Geotechnical, Inc.
Samples of the subsoils were taken with a 2 inch LD. spoon sampler. The sampler was
driven into the subsoils at various depths with blows from a 140 pound hammer falling 30
inches. This test is similar to the standard penetration test described by ASTM Method
D-1586. The penetration resistance values are an indication of the relative density or
consistency of the subsoils. Depths at which the samples were taken and the penetration
resistance values are shown on the Logs of Exploratory Borings, Figure 2. The samples
were returned to our laboratory for review by the project engineer and testing.
SUBSURFACE COMD1TLONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.
The subsoils consist of about one foot of topsoil overlying stratified sand, silt and clay.
About the upper 8 feet contained silty sand lenses or layers and the underlying soils were
mainly sandy clay and silt to a depth of 44 feet in Boring 2 where relatively dense gravel
was encountered.
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Laboratory testing performed on samples obtained from the borings included natural
moisture content and density and percent finer than sand size gradation analyses. Results
of swell -consolidation testing performed on relatively undisturbed drive samples,
presented on Figures 4 and 5, generally indicate low to moderate compressibility under
conditions of loading and wetting. The highly moist clay and silt sample from Boring 1
at 10 feet showed moderate to high compressibility under loading. The laboratory testing
is summarized in Table 1.
Free water was encountered in the borings at a depth of about 10 feet at the time of
drilling and the upper soils were slightly moist to moist. The borings were caved at a
depth of 81/2 to 10 feet when checked several day following drilling which probably
corresponds to the water level.
FOUNDATION BEARING CONDITIONS
The stratified sand and silt soils encountered at typical shallow foundation depth tend to
settle when wetted under load. A shallow foundation placed on the natural soils will have
a risk of settlement if the soils become wetted and care should be taken in the surface
grading around the house to prevent the soils from becoming wet. It will be critical to the
long term performance of the structure that the recommendations for surface grading and
drainage•contained in this report be followed. The amount of settlement, if the bearing
soils become wet, will mainly be related to the depth and extent of subsurface wetting.
We expect that initial settlements will be less than 1 inch. If wetting of the shallow soils
occurs, additional settlements of 1 to 11/2 inches could occur and could cause building
distress. Mitigation methods such as placing 3 feet of compacted structural fill below
foundations, a deep foundation (such as piles or piers extending down at least 40 feet
below existing ground surface to dense gravel) or a heavily reinforced mat foundation and
designed by the structural engineer can be used to support the proposed house with a
lower risk of settlement. If mitigation methods are desired, we should be contacted to
provide further design recommendations.
Job No. 116 098A
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4
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the
nature of the proposed construction, the building can be founded with spread footings
bearing on the natural soils below topsoil with a risk of settlement.
The design and construction criteria presented below should be observed for a spread
footing foundation system.
1) Footings placed on the undisturbed natural soils below topsoil should be
designed for an allowable bearing pressure of 1,200 psf. Based on
experience, we expect initial settlement of footings designed and
constructed as discussed in this section will be about 1 inch or less. The
soils are compressible under load after wetting and additional settlements
of 1 to 11/2 inches are possible depending on the depth and extent of
wetting.
2) The footings should have a minimum width of 20 inches for continuous
walls and 30 inches for isolated pads.
3) Exterior footings and footings beneath unheated areas should be provided
with adequate soil cover above their bearing elevation for frost protection.
Placement of foundations at least 36 inches below exterior grade is
typically used in this area.
4) Continuous foundation walls should be heavily reinforced top and bottom
to span local anomalies such as by assuming an unsupported length of at
least 14 feet. Foundation walls acting as retaining structures should also
be designed to resist a lateral earth pressure corresponding to an equivalent
fluid unit weight of at least 50 pcf.
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5) All topsoil and any loose or disturbed soils should be removed and the
footing bearing level extended down to the undisturbed natural soils. The
exposed soils in footing area should then be moistened and compacted.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINING WALLS
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and
equipment. The lateral earth pressure recommended above assumes drained conditions
behind the walls and a horizontal backfill surface. The buildup of water behind a wall or
an upward sloping backfill surface will increase the lateral pressure imposed on a
retaining structure. An underdrain should be provided to prevent hydrostatic pressure
buildup behind retaining walls.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisture content near optimum. Backfill placed in
pavement and walkway areas should be compacted to at least 95% of the maximum
standard Proctor density. Care should be taken not to overcompact the backfill or use
large equipment near the wall, since this could cause excessive lateral pressure on the
wall. Some settlement of deep foundation wall backfill should be expected, even if the
material is placed correctly, and could result in distress to facilities constructed on the
backfill.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab -
on -grade construction with a settlement risk. 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
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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 relatively well graded sand and
gravel (such as road base) should be placed beneath interior slabs for support. This
material should consist of minus 2 inch aggregate with at least 50% retained on the No. 4
sieve and less than 12% 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 devoid of vegetation and topsoil.
UNDERDRAIN SYSTEM
It is our understanding the finished floor elevation at the lowest level is at or above the
surrounding grade and the residence will over shallow crawlspace about 2 to 3 feet below
existing ground surface. Therefore, a foundation drain system is not required provided
grading and drainage recommendations presented below are followed. It has been our
experience in the area that local perched groundwater can develop during times of heavy
precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched
condition. We recommend below -grade construction, such as retaining walls, he
protected from wetting and hydrostatic pressure buildup by an underdrain system.
If the finished floor elevation of the proposed structure has a floor level below the
surrounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
SURFACE DRAINAGE
It will be critical to the satisfactory performance of the building to keep the bearing soils
dry. The following drainage precautions should be observed during construction and
maintained at all times after the residence has been completed:
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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.
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
areas and a minimum slope of 3 inches in the first 10 feet in paved 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 foundation walls. Consideration should be given to use
of xeriscape to reduce the potential for wetting of soils below the building
caused by irrigation.
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 borings drilled 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 borings and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions
lob No. 116 098A
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encountered during construction appear different from those described in this report, we
should be notified so that 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.
Respectfully Submitted,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
Louis E. Eller
Reviewed by:
Steven L. Pawlak, P.E.
LEE/ksw
Job No. 116 098A
GecEtech
1
LOT 6
N
\ N
\ \ `s��-,
\\ .\ \ .`
WELL \ \ \ \
s
` (5
N `�
BORING 1 \ \ 1 \
APPROXIMATE si)s
LOT 4 \ PROPOSED
\ \\ .)BUILD AREA NN\
s •
0_, S BORING 2 'S,� - c5u,
cep
L 1 W J \
_ `
t, \ \ \ \ 1
1
LOT3
I I
I I
L
LOT5
NOTES:
1) Lot boundaries and contours from subdivision
plat by High Country Engineering.
2) Building location approximated from field
staking by others.
116 098A
Ge�teCh
He•worth—Pawlak Geotechnical
APPROXIMATE SCALE:
1" = 100'
LOCATION OF EXPLORATORY BORINGS
Figure 1
Elevation - Feet
5385
5380
5375
5370
5365
5360
5355
5350
5345
BORING 1
ELEV. =5381'
P-4
�7/12
WC = 5.5
DD=101
5/12
WC=17.5
D0=103
-200=71
4/12
/ WC=23.0
DD -100
2/12
3/12
6/12
BORING 2
ELEV.=5380.5' 5385
14/12
10/12
WC -3.5
DD -103
//__, 3/12
WC =23.5
DD=101
l 3/12
2/12
/r 4/12
.Do
5340 Note: Explanation of symbols is shown on Figure 3.
5380
5375
5370
5365
5360
5355
5350
5345
5340
Elevation - Feet
116 098A
HEPWORTH•PAWLAK GEOTECHNICAL.
LOGS OF EXPLORATORY BORINGS
Figure 2
LEGEND:
,.1
-7
7/12
TOPSOIL; organic clayey silty sand, soft, slightly moist, brown.
SAND AND SILT (SM -ML); stratified, slightly clayey, loose/medium stiff to stiff, slightly moist to moist, brown.
CLAY AND SILT (CL -ML); sandy to stratified sand lenses, soft to medium stiff, very moist to wet, light brown to
brown.
GRAVEL (GM); silty, sandy, with cobbles, dense, wet, brown.
Relatively undisturbed drive sample; 2 -inch I.D. California liner sample.
Drive sample blow count; indicates that 7 blows of a 140 pound hammer falling 30 inches were
required to drive the California sampler 12 inches.
Free water level in boring at the time of drilling. Borings were dry to the caved depth when checked 20 days
following drilling.
Depth at which boring had caved when checked on April 28, 2016.
NOTES:
1. Exploratory borings were drilled on April 8, 2016 with 4 -inch diameter continuous flight power auger.
2. Locations of exploratory borings were measured approximately by pacing from features shown on the site plan
provided.
3. Elevations of exploratory borings were obtained by interpolation between contours shown on the site plan provided.
4. The exploratory boring 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 boring Togs represent the approximate boundaries between
material types and transitions may be gradual.
6. Water level readings shown on the logs were made at the time and under the conditions indicated. Fluctuations in
water level may occur with time.
7. Laboratory Testing Results:
WC = Water Content (%)
DD = Dry Density (pcf)
-200 = Percent passing the No. 200 sieve
116 098A
LEGEND AND NOTES
Figure 3
Compression %
Compression %
0
1
2
3
4
5
6
0
1
2
3
5
6
Moisture Content = 5.5 percent
Dry Density = 101 pcf
Sample of: Clayey Silty Sand
From: Boring 1 at 2 % feet
0.1
�ro
Compression
upon
wetting
1.0 10
APPLIED PRESSURE - ksf
100
Moisture Content = 3.5 percent
Dry Density = 103 pcf
Sample of: Clayey Sandy Silt
From: Boring 2 at 5 feet
0 -
Compression
upon
wetting
0.1
1.0 10
APPLIED PRESSURE - ksf
100
Compression %
co w C3)cn -P 0) iv 1 0 1
—
r,
Moisture Content = 23.0 percent
Dry Density = 101 pcf
Sample of: Sandy Caly and Silt
From: Boring 1 at 10 feet
No movement
upon
wetting
•
•
•
0.1 1.0 10 100
APPLIED PRESSURE - ksf
116 098A
H
Hepworth—Pawlok Geotechnical
SWELL-CONSOLIDATION TEST RESULTS
Figure 5
Job No. 116 098A
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Clayey Sandy Silt
Sandy Clay and Silt
Clayey Sandy Silt
Sandy Clay and Silt
LIQUID PLASTIC
LIMIT INDEX
(%) (%)
IL
MOISTURE j DRY GRAVEL SAND
BORING DEPTH CONTENT DENSITY
(%) (%)
(ft) j (%) (pcf)
,i
103
23.0 100
M
O
101
V'1
.:a
M
23.5
2 1/2
O
5_,)
.-4
N
5385
5380
5375
BORING 1
ELEV.=5381'
7/12
WC=5.5
DD -101
5/12
WC=17.5
DD -103
-200=71
1 4/12
BORING 2
ELEV. = 5380.5' 5385
14/12
10/12
WC= 3.5
DD=103
3/12
5380
5375
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V) 1
c m
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Or>
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O rn
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rn
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V960 914 '0N Qor
N
SAMPLE LOCATION
BORING DEPTH
(ft)
1 2 1/2
O
8
u,
10
iJi
23.5
w`I
23.0
NATURAL
MOISTURE
CONTENT
(%)
5.5
-
o
£OT
-
0
o
o 8
w
NATURAL
DRY
DENSITY
(pcf)
101
GRAVEL
(%)
GRADATION
o D
Z
v
71
PERCENT
PASSING
NO. 200
SIEVE
r- 7-
Iv
D
W
m
XJ
0
r
3
=1
PLASTIC
INDEX
(%)
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
Sandy Clay and Silt
Clayey Sandy Silt
Sandy Clay and Silt
Clayey Sandy Silt
SOIL TYPE
Clayey Silty Sand
V) 1
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