HomeMy WebLinkAboutSoils ReportSUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED DUPLEX
LOT D-18
ASPEN GLEN SUBDIVISION
GARFIELD COUNTY, COLORADO
.IOB NO. 115 020A
FEBRUARY 9, 2015
PREPARED FOR:
WOODBRIDGE MORTGAGE INVESTMENT FUND 2, LLC
ATTN: RICK SALVATO
22 CENTER STREET, FRONT SUITE
FREEHOLD, NEW JERSEY 07728
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - I -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION _ 3 -
SUBSURFACE CONDITIONS - 3 -
DESIGN RECOMMENDATIONS _ 4 -
FOUNDATIONS - 4
FLOOR SLABS - 5 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 6 -
LIMITATIONS - 7 -
REFERENCES _8 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - 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 duplex to be located at
Lot D-18, Aspen Glen Subdivision, 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 proposal for
geotechnical engineering services to you dated January 20, 2015. Chen -Northern, Inc.
(1991 and 1993) previously conducted preliminary geotechnical engineering studies for
the development and preliminary plat design.
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 duplex will be one and two story wood frame construction above a
crawlspace and with attached garages. Garage floors will be slab -on -grade. Grading for
the structure is assumed to be relatively minor with cut depths between about 3 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. 115 020A G ech
-2 -
SITE CONDITIONS
The vacant lot was covered with about 6 to 12 inches of snow at the time of our
exploration. Vegetation consists of grass and weeds. The area was graded during
subdivision development with probable shallow cuts at the site. The ground surface is
relatively flat with a slight slope down to the northwest. An irrigation ditch is located
along the rear property line.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen
development. These rocks are a sequence of gypsiferous shale, fine-grained
sandstone/siltstone and limestone with some massive beds of gypsum. There is a
possibility that massive gypsum deposits associated with the Eagle Valley Evaporite
underlie portions of the lot. Dissolution of the gypsum under certain conditions can cause
sinkholes to develop and can produce areas of localized subsidence. During previous
studies in the area, several broad subsidence areas and smaller size sinkhole areas were
observed scattered throughout the Aspen Glen development, predominantly on the east
side of the Roaring Fork River (Chen -Northern, Inc., 1993). These sinkholes appear
similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork
River valley.
Lot D-18 is located outside and about 400 feet east of one of the broad subsidence areas
mapped by Chen -Northern. Signs of active ground movements have not been observed in
the subsidence area. The nearest sinkhole was mapped about 950 feet to the northwest of
Lot D-18. Sinkholes were not observed in the immediate area of the subject lot. No
evidence of cavities was encountered in the subsurface materials; however, the
exploratory borings were relatively shallow, for foundation design only. Based on our
present knowledge of the subsurface conditions at the site, it cannot be said for certain
that sinkholes will not develop. The risk of future ground subsidence on Lot D-18
throughout the service life of the proposed duplex, in our opinion, is low but the site
Job No. 115 020A G&t h
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should not be considered totally risk free. If further investigation of possible cavities in
the bedrock below the site is desired, we should be contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on January 21, 2015. 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 1% inch and 2 inch I.D. spoon samplers. The
samplers were 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 tcst 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 CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.
The subsoils consist of about 11 to 13 feet of sandy silty clay overlying silty sandy gravel
with cobbles and boulders. Drilling in the dense granular soils with auger equipment was
difficult due to the cobbles and boulders and drilling refusal was encountered in the
deposit.
Laboratory testing performed on samples obtained from the borings included natural
moisture content and percent finer than sand size gradation analyses. Results of swell -
consolidation testing performed on relatively undisturbed drive samples, presented on
Job No. 115 020A Gggtech
-4 -
Figure 4, indicate low to moderate compressibility under conditions of loading and
wetting. The sample tested from Boring 2 at 8 feet showed a minor swell potential when
wetted. The laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the
nature of the proposed construction, we recommend the building be founded with spread
footings bearing on the natural sandy silty clay soils.
The design and construction criteria presented below should be observed for a spread
footing foundation system.
1) Footings placed on the undisturbed sandy silty clay soils should be
designed for an allowable bearing pressure of 2,000 psf. Based on
experience, we expect settlement/heave of footings designed and
constructed as discussed in this section will be about 1 inch or less.
2) The footings should have a minimum width of 18 inches for continuous
walls and 2 feet 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 arca.
4) 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 also be
Job No. 115 020A
-5 -
designed to resist a lateral earth pressure corresponding to an equivalent
fluid unit weight of at least 50 pcf.
5) All topsoil and any loose or disturbed soils should be removed and the
footing bearing level extended down to the relatively undisturbed soils.
The exposed soils in footing area should then be moistened and
compacted. If water seepage is encountered, the footing areas should be
dewatered before concrete placement.
6) 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 Iightly 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
basement level slabs to facilitate drainage. This material should consist of minus 2 inch
aggregate with at least 50% retained on 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 imported granular soils such as 34 inch road base devoid of oversized rock,
vegetation and topsoil.
Job No. 115 020A Gmech
- 6 -
UNDERDRAITI 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 or seasonal runoff. Frozen ground during spring runoff can create a perched
condition. We recommend below -grade construction, such as retaining walls and
crawispace 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, drywelI based in the
underlying gravel soils or sump and pump. 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 feet deep.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and
maintained at all times after the duplex has been completed:
1) Inundation of the foundation excavations and undcrslab 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
lab Ivo. 115 020A
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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.
Free -draining wall backfill should be capped with about 2 feet of the on-
site soils to reduce surface water infiltration.
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 I, 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
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
arc 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
Job No, 115 020A Gtech!
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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,
I-IEPWORTH - PAWLAK GEOTECHNICAL, INC.
Lout. E. Eller
Reviewed by:
Vit .0 E iii,
ODete� o
(S‘;',
e
Daniel E. Hardin, P.E. �'
•
219/fs
LEE/Ijf c� i 4<4
REFERENCES
Chen -Northern, Inc., 199 I, Preliminary Geoter•hnicul Engineering Study, Proposed
Aspen Glen Development, Gar/ielrl County, Colorado, prepared for Aspen Glen
Company, dated December 20, 1991, Job No. 4 112 92.
Chen -Northern, Inc., 1993, Geotechnical Engineering Study jOr Preliminary Plat Design,
Aspen Glen Development, Garfield County, Colorado, prepared for Aspen Glen
Company, dated May 28, 1993, Job No. 4 112 92.
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APPROXIMATE SCALE
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LOT D-19
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I BORING 2
•
PROPOSED
DUPLEX
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LOT D-18
• BORING 1
115 020A
H
UTILITY EASEMENT
Hepworth—Puwlok Geotechn col
LOT D-17
LOCATION OF EXPLORATORY BORINGS
1
Figure 1
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m
0
4
5
10
15
20
115 020A
BORING 1
—7
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12/12
10/12
WC= 6.7
D0=97
16/12
WC=10.1
DD=96
-200=94
i di
T
BORING 2
8/12
WC=8.7
DD= 100
-200=85
9/12
WC -15.4
DD=107
84/12
Note: Explanation of symbols is shown on Figure 3.
H
Hepworth—Pawlak Geotedmreal
—
LOGS OF EXPLORATORY BORINGS
0
5
10
15,E
20
Figure 2
LEGEND:
n
111
CLAY (CL); sandy, silty to very silty, stiff to very stiff with depth, red, low plasticity, upper 6 inches organic, upper
portion porous.
GRAVEL (GM); with cobbles and boulders, sandy, silty, dense, slightly moist, brown, subrounded rock.
Relatively undisturbed drive sample; 2 -inch LD. California liner sample.
Drive sample; standard penetration test (SPT), 1 3/8 inch ID. split spoon sample, ASTM D-1586.
16/12 Drive sample blow count; indicates that 16 blows of a 140 pound hammer failing 30 inches were
required to drive the California or SPT sampler 12 inches.
r
Practical drilling refusal.
NOTES:
1. Exploratory borings were drilled on January 21, 2015 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 not measured and the togs of exploratory borings are drawn to depth.
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. No free water was encountered in the borings at the time of drilling. Fluctuation in water level may occur with time.
7. Laboratory Testing Results:
WC = Water Content (%)
DD = Dry Density (pc()
-200 = Percent passing No. 200 sieve
115 020A
1-I
Hepworth—Pawlaic Geotechnlcol
LEGEND AND NOTES
Figure 3
Compression %
Compression - Expansion %
0
1
2
3
4
5
1
0
1
2
Moisture Content C 6.7 percent
Dry Density = 97 pcf
Sample of: Sandy Silty Clay
From: Boring 1 at 5 Feet
No movement
upon
wetting
0.1
.0 10
APPLIED PRESSURE - ksf
100
Moisture Content = 15.4 percent
Dry Density = 107 pcf
Sample of: Slightly Sandy Silty Clay
From: Boring 2 at 8 Feet
Expansion
upon
wetting
0.1
1.0 10
APPLIED PRESSURE - ksf
100
115 020A
H
Hapwor h--Pawlak Ceotsehnlcol
SWELL -CONSOLIDATION TEST RESULTS
Figure 4
Job No. 115 020A
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