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HEPWORTH—PAWLAK GEOTECHNICAL
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SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 68, SPRINGRIDCE RESERVE PUD, PIIASE 3
HIDDEN VALLEY DRIVE, GARFIELD COUNTY, COLORADO
,10B NO. 115 239A
JUNE 24, 2015
PREPARED FOR:
JAMES NIMMO
1172 MT. EVANS BOULEVARD
PINE, COLORADO 80470
{ jnitnnno26(u)yahoo.com)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION _ 1 -
SITE CONDITIONS - 1 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS - 4 -
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 THROUGH 6 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Job No. 115 239AbeCh
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located
on Lot 68, Springridge Reserve PUD, Phase 3, Hidden Valley Drive, 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 James Ninuno
dated May 27, 2015.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils and bedrock 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 a one story wood frame structure over a crawlspace. The
attached garage floor will be slab -on -grade. Grading for the structure is assumed to be
relatively minor with cut depths between about 3 to 5 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 reconunendations contained in this report.
SITE CONDITIONS
At the time of our field exploration the lot was vacant and vegetated with grass and
weeds. The southern side of the lot slopes moderately steep down to the northeast,
Job No. 115 239A GgrEtech
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adjacent to Hiddcn Valley Drive. The building area was gently sloping down to the
north.
FIELD EXPLORATION
The field exploration for the project was conducted on May 29, 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 a 2 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 and hardness of the bedrock. 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 1 to 2 feet of topsoil overlying 25 to 41 feet of medium stiff
to very stiff, sandy silty clay. Sandstone bedrock was encountered at depths of 27 and 42
feet in the borings.
Laboratory testing performed on samples obtained from the borings included natural
moisture content, dry density and percent finer than sand size gradation analyses. Results
of swell -consolidation testing performed on relatively undisturbed drive samples,
presented on Figures 4 through 6, indicate the sandy silty clays have low to moderate
compressibility under conditions of loading and a minor swell potential when wetted
under a light surcharge. The laboratory testing is summarized in Table 1.
Job No. 115 239A ech
-3 -
No free water was encountered in the borings at the time of drilling or when checked 23
days later and the subsoils were slightly moist to moist.
FOUNDATION BEARING CONDITIONS
The clay soils are somewhat variable with respect to density and swell/compressibility
potential. The clay soils can support lightly loaded spread footings with a low bearing
pressure and minor expansion potential particularly if the bearing soils become wet. If
the expansion risk for bearing on the clays is not acceptable, the underlying bedrock is
hard and could support a pier or pile foundation with low movement potential. If a deep
foundation is proposed, we should be contacted for additional recommendations.
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 clay soils with a risk of potential movement if the bearing
soils become wet.
The design and construction criteria presented below should be observed for a spread
footing foundation system.
1) Footings placed on the undisturbed natural clay soils should be designed
for an allowable bearing pressure of 2,000 psf. Based on experience, we
expect movement 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.
Job No. 115239A
-4-
4) Continuous foundation walls should be 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 lateral earth pressures as discussed in the "Foundation
and Retaining Walls" section of this report.
5) All existing fill, topsoil and any loose or disturbed soils should be removed
and the footing bearing level extended down to the relatively firm natural
soils. The exposed soils in footing area should then be moistened to near
optimum 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
Foundation walls and retaining structures which are laterally supported and can be
expected to undergo only a slight amount of deflection should be designed for a lateral
earth pressure computed on the basis of an equivalent fluid unit weight of at least 55 pcf
for backfill consisting of the on-site soils. Cantilevered retaining structures which are
separate from the residence and can be expected to deflect sufficiently to mobilize the full
active earth pressure condition should be designed for a lateral earth pressure computed
on the basis of an equivalent fluid unit weight of at least 45 pcf for backfill consisting of
the on-site soils.
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
walls and a horizontal backfill surface. The buildup of water behind a wall or an upward
sloping backfitl 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 near optimum moisture content. Backfill in pavement and
Job No. 115 239A eigcrstech
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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 Iarge 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.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure
against the side of the footing. Resistance to sliding at the bottoms of the footings can be
calculated based on a coefficient of friction of 0.30. Passive pressure of compacted
backfill against the sides of the footings can be calculated using an equivalent fluid unit
weight of 300 pc£ The coefficient of friction and passive pressure values recommended
above assume ultimate soil strength. Suitable factors of safety should be included in the
design to limit the strain which will occur at the ultimate strength, particularly in the case
of passive resistance. Fill placed against the sides of the footings to resist lateral loads
should be compacted to at least 95% of the maximum standard Proctor density at a
moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -
on -grade construction. There could be a risk of slab movement if the underlying soils
become wet. 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.
Job No. 115 239A
-6 -
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 or a suitable imported soil 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 also 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. 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. An impervious membrane, such as
20 mil PVC should be provided below the drain gravel in a trough shape and attached to
the foundation wall with mastic to prevent wetting of the bearing soils.
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
Job No. 115 239A G@c tiech
-7-
pavcmcnt 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.
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 Iocated at
Ieast 5 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
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. 115 239A
-8 -
this report ha,, been prepared for tilt. cm_lusive use by uur client for design purposes. We
are not responsible !or technical interpretations by others o!'our information. As the
project evolves, we should provide continued consultation and field services during
construction to review and monitor the implementation olour recommendations. and to
verily 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 till by a representative of the geotechnical
engineer.
Respectfully Submitted.
t IEPWOR"TI"I - PAWLAK GEOTECHNICAL. INC.
12 LGC -� 42L' Cia,
Andrew- R. Spickert
Rei iew ed by:
Ato
Daniel C. Hardin. P.E. i
ARS/ksw jk. -` r
(ijt
Job No. 1 15 339,1
Gec,tech
OPEN SPACE
1
r
LOT 62
BORING 1
•
LOT 68
•
BORING 2
1
16UILDING SETBACK UNE
---.........-----.....-__-_-.1
APPROXIMATE SCALE
1" _ Rnp
LOT 67
,,, ,
_ ,____,, , ,_ ,,_____„___
HIDDEN VALLEY DRIVE
115 239A
HCPWISRTH pAwLAK GROTBCHNICAL
LOCATION OF EXPLORATORY BORINGS
Figure 1
Elevation - Feet
Q
5
10
15
L
20
25
30
35
40
115239A
BORING 1
ELEV.= 6463'
5/12
WC=20.3
00=99
9/12
WC=16.8
DD=106
-200=86
8/12
WC=16.1
DID= 110
13/12
WC=11.8
DD=113
-200=69
BORING 2
ELEV.= 6466'
Note: Explanation of symbols is shown on Figure 3.
H
HEPWDR'TKPAWLAK GEO18CHNICAL
11/12
24/12
WC=6.5
00=107
12/12
WC=129
00=115
11/12
WC=14.0
00=114
28/12
WC= 12.5
DD= 120
-200=62
BORING 2
CONT.
,V
;�c 50/3
BOTTOM OF BORING
AT 46 FEET
LOGS OF EXPLORATORY BORINGS
0
5
10 —
15
20
25
30
35
40 �.
Figure 2
Elevation - Feet
LEGEND:
® TOPSOIL; clay, sandy, silty, moist, brown, organic.
b
5/12
CLAY (CL); sandy, silty, medium stiff to very stiff, slightly moist to moist, brown to red -brown, can be
slightly calcareous in places.
SANDSTONE BEDROCK; hard, slightly moist, red. Maroon Formation.
Relatively undisturbed drive sample; 2 -inch LD. California liner sample.
Drive sample blow count; Indicates that 5 blows of a 140 pound hammer falling 30 Inches were
required to drive the California sampler 12 inches.
NOTES:
1. Exploratory Borings were drilled on May 29, 2015 with 4-1nch 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 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 or when checked 23 days later. Fluctuation in
water level may occur with time.
7. Laboratory Testing Results:
WC = Water Content (%)
DD = Dry Density (pcf)
-200 = Percent passing No. 200 sieve
115 239A
F ePwo }+PAW.AK GeorecHPpcAL
LEGEND AND NOTES
Figure 3
co
2
E 0
Expansion - Compression %
3
1
0
1
2
3
4
Moisture Content = 16.8 percent
Dry Density = 106 pcf
Sample of: Sandy Silty Clay
From: Boring 1 at 5 Feet
0.1
No movement
upon
wetting
1.0 10
APPLIED PRESSURE - ksf
100
Moisture Content = 16.1 percent
Dry Density = 110 pcf
Sample of: Sandy Silty Clay
From: Boring 1 at 10 Feet
Expansion
upon
wetting
0.1
115 239A
Ink
1.0 10
APPLIED PRESSURE- ksf
HEPWOR H PAwLAR GEO'SECHNICAI.
SWELL -CONSOLIDATION TEST RESULTS
100
Figure 4
Expansion - Compression %
Expansion - Compression %
1
0
1
2
3
1
0
1
2
3
4
0.1
.0 10
APPLIED PRESSURE - ksf
100
Moisture Content = 6.5 percent
Dry Density = 107 pcf
Sample of: Silty Sandy Clay
From: Boring 2 at 5 Feet
-----------_______________:
Expansion
upon
wetting
Expansion
upon
wetting
i
J
0.1
.0 10
APPLIED PRESSURE - ksf
100
0.1
115 239A
1.0 10
APPLIED PIRESSSURE - ksf
H PwoRTH-PAwI.AK GEOTECHNICAL
100
SWELL -CONSOLIDATION TEST RESULTS Figure 5
Moisture Content = 12.9 percent
Dry Density = 115 pcf
Sample of: Silty Clay
From: Boring 2 at 10 Feet
Expansion
upon
wetting
i
J
0.1
115 239A
1.0 10
APPLIED PIRESSSURE - ksf
H PwoRTH-PAwI.AK GEOTECHNICAL
100
SWELL -CONSOLIDATION TEST RESULTS Figure 5
3
4
1 111111 Moisture Content = 14.0
Dry Density = 114
Sample of: Sandy Silty Clay
From: Boring 2 at 15 Feet
.1191 No Mment
upon Movement
ill II
wetting
11111 111111
1111
0.1
115 239A
H
1.0
percent
pct
10
APPLIED PRESSURE - Isf
SWELL -CONSOLIDATION TEST RESULTS
100
Job No. 115 239A
SOL OR
BEDROCK TYPE
Silty Clay
Sandy Silty Clay
Sandy Silty Clay
Silty Clay
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