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Geotech
HEPWORTH-PAWLAK GEOTECHNICAL
Hepworth-Pawlak Geotechnical, Inc.
5020 County Road 154
Glenwood Springs, Colorado 81601
Phone: 970-945-7988
Fax: 970-945-8454
Email: hpgeo@hpgeotech.com
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT GV5, ASPEN GLEN
PRIMROSE LANE
GARFIELD COUNTY, COLORADO
JOB NO. 116 273A
JUNE 30, 2016
PREPARED FOR:
GREGORY FRIEDMAN
71 GOLDEN BEAR DRIVE
CARBONDALE, COLORADO 81623
(gaf iib!ucrivernet.com)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION - 3 -
SUBSURFACE CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS -4-
FOUNDATION AND RETAINING WALLS - 5 -
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 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located at
Lot GV5, Aspen Glen, Primrose Lane, 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 you dated June 23, 2016. Chen -Northern, Inc.
previously conducted geotechnical engineering studies for the Aspen Glen development
and presented their findings in reports dated December 20, 1991 and May 28, 1993, Job
No. 4 112 92.
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 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 one and two story wood frame construction with an
attached garage. Ground floor will be structural above a crawlspace or basement level.
The garage floor will be slab -on -grade. Grading for the structure is assumed to be
relatively minor with cut depths between about 3 to 8 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.
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SITE CONDITIONS
The vacant lot is located in the southwestern part of the subdivision and on the south side
of the Roaring Fork River. Vegetation consists of grass and weeds. The ground surface
slopes away from Primrose Lane, gently at first but becoming steeper at the northern end
of the lot.
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 sinkholes were
observed scattered throughout the Aspen Glen development (Chen -Northern, Inc. 1991
and 1993). These sinkholes appear similar to others associated with the Eagle Valley
Evaporite in areas of the Roaring Fork River valley. The lot is not located within a broad
subsidence area and existing sinkholes were not observed in the immediate area of the
subject lot. The closest mapped sinkhole is about 1600 feet west of this 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 GV5 throughout the service life of
the proposed residence, in our opinion, is low; however, the owner should be made aware
of the potential for sinkhole development. If further investigation of possible cavities in
the bedrock below the site is desired, we should be contacted.
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FIELD EXPLORATION
The field exploration for the project was conducted on June 28, 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 1% inch I.D. 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 CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.
The subsoils, below about four inches of topsoil, consist of about 1 to 11/2 feet of sandy
silt and clay overlying dense silty sandy gravel with cobbles and small 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 gradation analyses. Results of gradation analyses performed on
small diameter drive samples (minus 1'/2 inch fraction) of the coarse granular subsoils are
shown on Figure 4. The laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling. The subsoils were
slightly moist to moist.
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DESIGN RECOMMENDATIONS
FOUNDATION S
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 granular soils.
The design and construction criteria presented below should be observed for a spread
footing foundation system.
1)
Footings placed on the undisturbed natural granular soils should be
designed for an allowable bearing pressure of 3,000 psf. Based on
experience, we expect settlement 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 16 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 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 retaining structures should also be
designed to resist a lateral earth pressure corresponding to an equivalent
fluid unit weight of at least 50 pcf.
5) The topsoil, silt and clay soils and any loose or disturbed soils should be
removed and the footing bearing level extended down to the relatively
undisturbed natural soils. The exposed soils in footing area should then be
moistened and compacted. Voids created by boulder removal or sub -
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excavation of silt and clay soils can be backfilled with granular structural
fill compacted to at least 98% of standard Proctor density.
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 pressures recommended above assume drained conditions behind the
Ll walls and a horizontal backfill surface. The buildup of water behind a wall or an upward
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sloping backfill surface will increase the lateral pressure imposed on a foundation wall or
retaining structure. An underdrain should be provided to prevent hydrostatic pressure
buildup behind 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, 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
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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 slabs. 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 the on-site granular soils or a suitable imported gravel 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 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
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:
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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 6 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 finer graded soils to reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
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
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.
Job No. 116 273A
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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.
Tom C Brunner, Staff Engineer
Reviewed by:
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Steven L. Pawlak, P. E e �� f ...
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;FERENCES
Chen -Northern, Inc., 1991, Preliminary Geotechnical Engineering Study, Proposed
Aspen Glen Development, Garfield County. Colorado, prepared for Aspen
Glen Company, dated December 20, 1991, Job. No. 4 112 92.
Chen -Northern, Inc., 1993, Geotechnical Engineering Study firr Preliminary Plat Design,
Aspen Glen Development, Garfield County. Colorado, prepared for Aspen Glen
Company, dated May 28, 1993, Job. No. 4 112 92.
Job No. 116 273A
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LOT GV9
LOT GV4
APPROXIMATE SCALE
1"=40'
LOT GV7
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BUILDING ENVELOPE
LOT GV6
HP GEOTECH
JOB NO. 115 569A
PRIMROSE LANE
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5
10
BORING 1
ELEV.-6054'
sch
4 04�
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69/12
WC=1.7
+4=49
81/11 -200=15
50/3
BORING 2
ELEV.=6059'
•eOp
o!" 50/6
= -sa 50/5
50/2
0
5
10
15 15
Note: Explanation of symbols is shown on Figure 3.
116 273A
LOGS OF EXPLORATORY BORINGS
Figure 2
LEGEND:
111
39/12
TOPSOIL; roots, organics, clayey, sandy, very silty, medium stiff, slightly moist to moist, reddish brown.
CLAY AND SILT (CL -ML); sandy, slightly gravelly, medium stiff, slightly moist to moist, reddish brown.
SAND AND GRAVEL (SM -GM); silty, cobbles and boulders, dense to very dense, slightly moist, brown to
reddish brown, rounded rocks. -
Drive sample; standard penetration test (SPT), 1 3/8 inch I.D. split spoon sample, ASTM D-1586.
Drive sample blow count; indicates that 39 blows of a 140 pound hammer falling 30 inches were
required to drive the SPT sampler 12 inches.
Practical Drilling Refusal
NOTES:
1. Exploratory borings were drilled on June 28, 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.
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 occur with time.
7. Laboratory Testing Results:
WC = Water Content (%)
+4 = Percent retained on the No. 4 sieve
-200 = Percent passing No. 200 sieve
116 273A
HEPWORTH-PAWLAK GEOTECHNICAL
LEGEND AND NOTES
Figure 3
:10: 10BIaaEMM'
HYDROMETER ANALYSIS SIEVE ANALYSIS
4 Hq TIME READINGS U S. STANDARD SERIES 1 CLEAR SQUARE OPENINGS I
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
100
.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
1.
1
4
1
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT
COBBLES 0 %
LIQUID LIMIT
SANIT
1 vI GIN 1COVASr
GRAVEL 49 % SAND 36 %
%
SAMPLE OF: Silty Very Sandy Gravel
FIT4 1 COARSE_
PLASTICITY INDEX
COBBLES
SILT AND CLAY 15 %
90
80
70
60
50
40
30
20
10
0
FROM: Boring 1 at 212 and 5 Feet Combined
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HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Job No. 116 273A
SAMPLE LOCATIONNATURAL
GRADATION
ATTERE3ERG LIMITS
BORING
DEPTH
(ft)
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(pct)
GRAVEL
o
(/u)
SAND
(%)
PASPERCENT
NO.PLASTICING
200
SIEVE
LIQUID
LIMIT
(%)
INDEX
(%)
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
SOIL OR
BEDROCK TYPE
1
21/z and 5
combined
1.7
49
36
15
Silty Very Sandy Gravel
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