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SUBSOIL STUDY
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FOR FOUNDATION DESIGN
PROPOSED DUPLEX
LOT D-19
ASPEN GLEN SUBDIVISION
GARFIELD COUNTY, COLORADO
JOB NO. 115 021A
FEBRUARY 9, 2015
PREPARED FOR:
., .
WOODBRIDGE MORTGAGE INVESTMENT FUND 2, LLC
ATTN: RICK SALVATO
22 CENTER STREET, FRONT SUITE
FREEHOLD, NEW JERSEY 07728
(rh:i h <!1 ;ml.mm)
TABLE OF CONTENTS
PlJRPOSE AND SCOPE OF STUDY ............................................................................ - 1 -
PROPOSED CONSTRUCTION ....... _ ........................................................................... -1 -
SITE CONDITIONS ....................................................................................................... -2 -
SUBSIDENCE POTEN"l'IAL ......................................................................................... -2 -
FIELD EXPLORATION ................................................................................................. -3 -
SUBSURFACE CONDITIONS ...................................................................................... -3 -
DESIGN RECOMMENDATIONS ................................................................................ -4 -
FOUNDATIONS ........................................................................................................ - 4 -
nooR SLABS ........................................ , ........................................................ , ........ -... _.-5 -
UNl)ERDRA.IN SYSTEM .................................. .,. ...................................................... -6 -
SURFACE DRAIN'AGE ............................................................................................. -6 -
Lll\1.IT A TIO NS ................................................. -.............................. +.+•· .. •••••·•••••·••••• ................... -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
PURPOSEANDSCOPEOFSTUDY
This report presents the results of a subsoil study for a proposed duplex to be located at
Lot D-19, Aspen Glen, Garfield County, Colorado. The project site is shown on Figure l.
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 Woodbridge Mortgage Investment Fund 2, LLC dated January 20, 2015.
Chen-Northern, Inc. (1991and1993) previously conducted preliminary gcotechnical
engineering studies for the development and preliminary plat design.
A field exploration program consisting of exploratory borings was conducted to obtain
infonnation on the subsurface conditions. Samples of the subsoils obtained during the
field exploration were tested in the laboratory to detennine 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 b~ed 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 ~arages. Garage floors will be slab-on-grade .. Grading for
the structure is assumed to be relatively minor with cut depths between abqut 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 02JA
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SITE CONDITIONS
The vacant Jot 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 POTE.NTIAL
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-19 is located outside and about 450 feet east of one of the broad subsjdence areas
mapped by Cbcn-Nonhem. Signs of active ground movements have not been observed in
the subsidence area The nearest sinkhole was mapped about 1000 feet to the northwest
of Lot D-19. Sinkholes were not observed in the immediate area of the subject lot. No
evidence of cavities was encoumcred in the subsurface materials; however, the
exploratory borings were relatively shaUow, for foundation design only. Based on our
present knowledge of the subsurface conditions at the site, it cannot be s~d for certain
that sinkholes wiJl not develop. The risk of future ground subsidence on Lot D-19
throughout the service life of the proposed duplex . i n our opinion, is low but the site
Job No. I IS 021A
-3-
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 b~rings were drilled at the locations shown on Figure l 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 Geotcchnical, 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 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 CONDITIONS
Graphic logs of the subsurface conditions encountered al the site are shown on Figure 2.
The subsoils consist of about 10 feet of sandy silty clay overlying silty sandy gravel with
cobbles and boulders. Drilling in the dense granular soils with auger equipment was
difficuJt 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 then sand gradation analyses. Results of swell-
consolidation testing perfonned on relatively undisturbed drive samples, presented on
JobNo. llS021A
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Figure 4, indicate low to moderate compressibility under conditions of loading and
wetting. The sampJes showed a low swell potentiaJ 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 cJay soils .
The design and construction criteria presented below should be observed for a spread
footing foundation system.
1) Footings placed on the undisturbed natural 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 I 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 areac; 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 reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 12
feet. Foundation walls acting as retain ing structures should also be
Job No. I IS 021A
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designed to resist a lateral earth pressure corresponding to an equivalent
fluid unit weight of at least SO pcf.
5) AH topsoil and any loose or disturbed soiJs 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 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
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 % inch road base devoid of oversized rock,
vegetation and topsoil.
Job No. 115 021A
-6 -
UNDERDRAINSYSTEM
Although free water was not encountered during our exploration , it has been our
experience in the area that local perched groundwater can develop during ti mes 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
crawlspace areas, be protected from wetting and hydrostatic pressure buildup by an
underdrnin system.
The drains should consist of drainpipe placed in the bottom of the wall backfill
surrounded above the invert level with f ree-draining granular material. The drain should
be placed at each level of excavation and at least 1 foot below lowest adjacent fi ni sh
grade and sloped at a minimum 1% to a suitable gravity outlet, drywell 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 1 ~ 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 unders lab 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 den sity i n
pavement and sl ab areas and to at least 90% of the maximum stand ard
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 sl ope of 12 inches iu the first lO feet in unpaved
Job No. l!S 021A
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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-
sitc soils to reduce surface water inftltration.
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 IO 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 gcotechnical
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 arc
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 e;icploratory borings and variations in the subsurface
condiLions may not become evident until excavation is perfonned. 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
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 rccommendaLions have been appropriately interpreted. Significant design
Job No. llS 021A
changes may require additional analysis or modilications to the recommendations
presented herein. We recommend on-site observation of excavations and foundation
bearing strata and teMing of structural Ii II by a representative of the geotechnical
engineer.
Respectfully Submillcd ,
l-IEPWORTll ·PAWLAK GEOTECHNICAL, INC.
Louis E. Eller
Reviewed by:
LEE/ljf
REFERENCES
Chen-Northern, Inc., 1991, Preliminary Geotedmical £11gi11eeri11g Srm(r. Proposed
A.\1Jl'll Glen De1 ·e/opme111. Gmjidcl Cmmty. Colomdo. prepared for Aspen Glen
Company, dated December 20, 1991, Job No. 4 112 92.
Chen -Northern, Inc., 1993, G,·oredmicnl Engi11eeri11g S111clyfor Pn:liminm:r Plat Design ,
Aspe11 Gh•n Dt•1 ·e/opm e111 . Gmfieltl Cou111y. Colorado. prepared for Aspen Glen
Company. da ted May 28, 1993 . Job No. 4 112 92.
~ech
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APPROXIMATE SCALE
1· = 30'
/
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// \
/ \
/ \
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// \ \
/ \ \
// \
/ \
// '\ \ / \
// / \
// '
// ~ \ ---/ \ /,,-\
I / LOTD-19 \
( ( . ~ \
\ BORING2 \
LOT D-18
\ \ ~ \ \
\ PROPOSED \
\ \ WPLEX \ \
I BORING 1 ·~ \
t I_ ' I ~G SETBACK LINE \
I \
r \ L_______ \
------------------------~
IRRIGATION DITCH
LOTC-1
115 021A G5'~ LOCATION OF EXPLORATORY BORINGS Figure 1
He warttt-Pawlak Geotedvllcol
BORING 1 BORING2
0 0
9/1 2
12/12
WC=S.4
5 0Du98 5 12/12 -200=83
WC=11 .3
00=99
9/12
WC=B .7
ii) 00=93 '1il
if tf
I 10 3orl 10 • .c £ a. Cl.
Q) Q)
0 0
3516,10/0
15 15
20 20
Note: Exp lanation of symbols is shown on Figure 3.
115 021A LOGS OF EXPLORATORY BORINGS Figure 2
LEGEND:
CLAY (CL); sandy, silty to very silty, stirf to very stiff with depth, red, low plasticity, upper 6 Inches organic, upper
portion porous.
GRAVEL (GM); with cobbles and boulders, sandy, silly, dense, slightly moist, brown, subrounded rock.
9/12
T
NOTES:
Relatively undisturbed drive sample; 2-inch l.D . California liner sample.
Drive sample; standard penetration tesl (SPn. 1 3/8 inch 1.0. split spoon sample, ASTM D-1586.
Drive sample blow count; indicates thal 9 blows of a 140 pound hammer falling 30 inches were
required lo drive the California or SPT sampler 12 inches .
Practical drilling refusal.
1. Exploratory borings were drH!ed on January 21, 2015 with 4-inch diameter continuous night 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 logs 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 logs 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 0CC1Jr with time.
7. Laboratory Testing Results:
WC = Water Content (%)
DD = Dry Densily (pcf)
-200 = Percent passing No. 200 sieve
~
H91:1warth-Pawlak Gaiatechnlcal
115 021A LEGEND AND NOTES Figure 3
Moisture Content = 11.3 percent
Dry Density = 99 pcf
Sample of: Sandy Silty Clay
From: Boring 1 at 5 Feet
1
(fl. c~~ c
0 u; 0 a ~ "t a. " a'.i
• 1 ' c
.Q \ )
(/)
(/)
QI a. 2 E
0 Expansion
0 upon
wetting
0.1 1.0 10 100
APPLIED PRESSURE -ksf
Moisture Content = 8 .7 percent
2
Dry Density = 93 pcf
Sample of: Sandy Silty Clay
From: Boring 2 at 7 Feet
1 t I
~ ~ c: .Q 0 (/) c: ~ \ ro a.
in • 1 c: Expansion I c \ u; rn upon
!!? 2 wetting a.
E
0 \ 0
3
~
4
0.1 1.0 10 100
APPLIED PRESSURE -ksf
115 021A c.s''1ech
H111>warth-Pawlak Geatechnlcal
SWELL-CONSOLIDATION TEST RESULTS Figure 4
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1 Job No. 115 021A
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION NATURAL NATURAL GRADATION PERCENT AmRBERG LIMITS UNCONFINED
MOISTURE DRY GRAVEL SAND PASSING UQUID PU\STIC COMPRESSIVE SOIL OR BORING DEPTH CONTENT DENSITY NO. 200 UMIT INDEX STRENGTH BEDROO< TYPE (%) (%) SIEVE
lit\ t%\ (od\ 1%) {%\ (PSf\
1 5 11.3 99 Sandy Silty Clay
2 3 5.4 98 83 Sandy Silty Clay
7 8.7 93 Sandy Silty Clay