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HEPWORTH -PAWLAK GEOTECHNICAL
November 12, 2012
Gruenefeldt Construction
Attn: Dan Gruenefeldt
P.O. Box 1910
Basalt, Colorado 81621
dan@gruenefeldt.com
1..1\'.'1„'x).41 ‘.1:"I
k III
Job No. 112 397A
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot F26,
Aspen Glen. Bald Eagle Way, Garfield County, Colorado
Dear Dan:
As requested, Hepworth-Pawlak Geotechnical, Inc. performed a subsoil study for design
of foundations at the subject site. The study was conducted in accordance with our
agreement for geotechnical engineering services to you dated October 24, 2012. The data
obtained and our recommendations based on the assumed construction and subsurface
conditions encountered are presented in this report. We understand that the findings of
our report will be considered in the purchase of the lot.
Proposed Construction: The proposed residence design is preliminary but will likely be
a 1 to 2 story wood frame structure over a walkout basement with attached garage located
within the area of the building envelope as shown on Figure 1. Ground floors will be
slab -on -grade. Cut depths are expected to range between about 3 to 8 feet. Foundation
loadings for this type of construction are assumed to be relatively light and typical of the
proposed type of construction.
lfbuilding conditions or foundation loadings are significantly different from those
described above, we should be notified to re-evaluate the recommendations presented in
this report.
Site Conditions: The lot was vacant and is vegetated with grass and weeds. The terrain
is relatively flat near the street on the northwest side of the lot and slopes gently to
strongly down to the southwest at grades of 3 to 10% in the building area. Below the
building area the slope becomes moderately steep down to the west at about 25% grade.
The lot appears to have been graded during development of subdivision with shallow cuts
and fills. There is an active irrigation ditch on the east side of the lot. The lot to the east
across the ditch is developed with a 2 story residence. The lot to the west is vacant.
Subsidence Potential: Aspen Glen is underlain by Pennsylvania Age Eagle Valley
Evaporite bedrock, The evaporite contains gypsum deposits. Dissolution of the gypsum
under certain conditions can cause sinkholes to develop and can produce areas of
iO3-841-7 W) 9 Col( w,tkhl)Sprill!,•ti 7i`:) -6i3-55()? e Silv{•r[97C-4(i,`ti 1Uti-)
-2 -
localized subsidence. During previous work in the area, subsidence features were
observed in the Aspen Glen Subdivision. The nearest subsidence feature, or sinkhole, is
about 600 feet east of the subject site. Sinkholes were not observed in the immediate area
of the subject lot. The pits dug as part of this study were shallow, for foundation design
only. No evidence of sinkholes was observed in the pits. Based on our present
knowledge ofthe site, it cannot be said for certain that sinkholes will not develop. In our
opinion, the risk of ground subsidence at Lot F26 is low and similar to other lots in the
area but the owner should be aware ofthe potential for sinkhole development.
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavating seven exploratory pits at the approximate locations shown on Figure 1. The
logs ofthe pits are presented on Figure 2. The subsoils encountered, below about 1 to 5
feet of fill, consist of nil to 2 feet of stiff, sandy silty clay overlying relatively dense,
slightly silty sandy gravel with cobbles and scattered small boulders. Results of swell -
consolidation testing performed on a relatively undisturbed sample of the sandy silty clay
fill, presented on Figure 4, indicate low compressibility under existing moisture
conditions and light loading and a low collapse potential (settlement under constant load)
when wetted. The fill was moderately compressible under increased loading after
wetting, Results of a gradation analysis pertbrmed on a sample of the slightly silty sandy
gravel with cobbles (minus 5 inch fraction) obtained from the site are presented on Figure
5. No free water was observed in the pits at the time of excavation and the soils were
slightly moist to moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread
footings placed on the undisturbed natural granular soil designed for an allowable soil
bearing pressure of 3,000 psf for support of the proposed residence. The fill and clay
soils tend to compress after wetting and should be removed below footing areas.
Settlement of footings placed on the relatively dense gravel soils should be less than 1
inch. Footings should be a minimum width of 16 inches for continuous walls and 2 feet
for columns. Loose and disturbed soils and existing fill and clay soils encountered at the
foundation bearing level within the excavation should be removed and the footing bearing
level extended down to the undisturbed natural granular soils. Exterior footings should be
provided with adequate cover above their bearing elevations for frost protection.
Placement of footings at least 36 inches below the exterior grade is typically used in this
area. Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 10 feet. Foundation
walls acting as retaining structures should be designed to resist a lateral earth pressure
based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly
loaded slab -on -grade construction. We should further evaluate the suitability of the fill
for support of floor slabs at the time of construction. To reduce the effects of some
differential movement, floor slabs should be separated frorn 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
Job No. 112 397A
GgEftecti
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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 less than 50% passing 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
also create a perched condition. We recommend below -grade construction, such as
retaining walls, crawlspace and basement areas, be protected from wetting and
hydrostatic pressure buildup by an underdrain system. Areas, such as the garage, where
the interior slab grade is at or above the exterior ground elevation should not need an
underdrain.
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 feast 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:
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. Free -draining wall backfill should be
capped with about 2 feet of the on-site, finer graded soils to reduce surface
water infiltration.
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 pavement and
walkway areas.
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
Job No. i 12 397A
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warranty either express or implied. The conclusions and recommendations submitted in
this report are based upon the data obtained from the exploratory pits excavated at the
locations indicated on Figure 1 and to the depths shown on Figure 2, 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. lithe 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 pits 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 at once so 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.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
HEPWORTH - PAWLAK GEOTECHNICAL, INC.
moo
REG J.
Daniel E. Hardin, P.
David A. Young, P
DEH/ksw
attachments Figure I
Figure 2
Figure 3 -
Figure 4
Figure 5 -
- Location of Exploratory Pits
- Logs of Exploratory Pits
Legend and Notes
- Swell -Consolidation Test Results
Gradation Test Results
Job No. 112 397A
APPROXIMATE SCALE:
1"=401
vk
HEPWORTH•PAWLAK GEOTECHNICAL
10
PIT 1
ELEV.= 6058.0'
PIT 3
ELEV. =6054.0'
grj
qa
PIT 4
ELEV. =6052.0'
10
10
PIT6
ELEV. =6056.0'
WC= 8.8
DD=104
PIT 2
ELEV. =6056.5'
-: +4 = 63
-200 = 12
t
PIT 5
ELEV. = 6056.0'
PIT 7
ELEV. =6057.0'
/
LOGS OF EXPLORATORY PITS
10
10
10
FIGURE 2
LEGEND:
FILL; mixture of sandy clay and silty sandy gravel with cobbles, moist, brown.
CLAY (CL); silty, sandy, stiff, slightly moist, brown.
GRAVEL; sandy, slighlty silty, medium dense to dense, slightly moist, light brown with cobbles and scattered
small boulders.
Relatively undisturbed 2 -inch diameter liner sample.
Disturbed bulk sample.
NOTES:
1. Exploratory pits were excavated on October 26, 2012 with a backhoe.
2. Locations of exploratory pits were measured approximately by pacing from features shown on the site plan provided.
3. Elevations of exploratory pits were obtained by interpolation between contours shown on the site plan provided.
4. The exploratory pit 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 pit logs represent the approximate boundaries between
material types and transitions may be gradual.
6. No free water was encountered in the pits at the time of excavating. Fluctuation in water level may occur with time.
7. Laboratory Testing Results:
WC = Water Content (% )
DD = Dry Density ( pcf )
+4 = Percent retained on the No. 4 sieve
-200 = Percent passing No. 200 sieve
112 397A
HEPWO RTH-PAWLAK GEOTECH NICAL
LEGEND AND NOTES
FIGURE 3
Moisture Content = 8.8 percent
Dry Density = 104 pcf
Sample of: Sandy Silty Clay {Fill)
From: Pit 6 at 3 Feet
Compression
2
3
Compression
upon
wetting
0.1
1.0 10
APPLIED PRESSURE -- ksf
112 397A
100
SWELL -CONSOLIDATION TEST RESULTS FIGURE 4
HEPWORTH-PAWLOA GEOTECHNICAL
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DIAMETER OF PARTICLES IN MIWMETERS
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LIQUID LIMIT %
111111111111.111t. # 1
1111111111/: MEM 31111.1111.4 :
SAND 25 %
SILT AND CLAY 12 %
PLASTICITY INDEX %
SAMPLE OF: Slightly Silty Sandy Gravel with Cobbles FROM: Pit 2 at 4 to 6 Feet
GRADATION TEST RESULTS
a_aaaaa.
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FIGURE 5
August 30, 2013
Gruenefeldt Construction
Attn: Dan Gruenefeldt
P.O. Box 1910
Basalt, Colorado 81621
Cltifl(a C tl. Ci�.:i� )Ci�.c;_ IH
Job No. 112 397A
Subject: Second Review of Site Grading Plan, Proposed Residence, Lot F26, Aspen
Glen, Bald Eagle Way, Garfield County, Colorado
Dear Dan:
As requested, we reviewed the new proposed site grading as shown on Plan Sheet SG -1.
"Grading Plan" updated August 29, 2013, by Christie .Jensen, Landscape Architect, for
the subject site. We previously reviewed the site grading plan as described in a letter
dated August 14, 201.3 and conducted a. subsoil study for design of foundations at the site
and presented our findings in a report dated November 12, 2012, Job No. 112 397A.
The plan shows grading of driveway and patio slabs as sloping away from the residence
at a minimum 2% grade. The surface grading in the landscape areas right around the
house has been better defined and varies from 5% on the north (front entrance) side of the
house to 3% off the patio walkway on the southeast side of the house. Based on the
subsoil conditions encountered at the site, these slopes should be adequate to drain
surface water away from the house foundation walls. The area between the garage and
the proposed berm at the north side of the garage will be graded at 5% to a catch basin
which drains toward the street. Three lawn drains are proposed between the driveway
and the front entry area of the house. These drains are piped to daylight on the slope
below the house to the west.
Considering the subsoil conditions, the current grading plan appears adequate.
If you have any questions or need further assistance, please call our office.
Sincerely,
HEPWORTI-I
Daniel E. 1larcl
DEH/ksw
PAWLAK GEO`��;I-JNICAL, INC.
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August 14. 2013
Gruenefcldt Construction
Attn: Dan Gruenefeldt
P.O. Box 1910
Basalt, Colorado 81621
dan(fltrue nc1c_idl .o 1m
Job No. 112 397A
Subject: Review of Site Grading Plan, Proposed Residence, Lot F26, Aspen Glen, 13a.1d
Eagle Way, Garfield County, Colorado
Dear Dan:
As requested, we reviewed the proposed site grading as shown on Plan Sheet AG -1
"Grading Plan" dated August 1 3, 2013, by Christie Jensen, Landscape Architect. for the
subject site. We previously conducted a subsoil study for design of foundations at the site
and presented our findings in a report dated November 12, 2012; Job No. 112 397A.
The plan shows grading of driveway and patio slabs as sloping away from the residence
at a rninicnurn 2% grade. The surface grading in the landscape areas is not as well defined
right around the house. It should slope away from the house at a minimum 5% grade to
be in accordance with the 2009 International Residential Code. Based on our experience
in the area, we had recommended a slope of 10% away from the house. The proposed
bcrna at the north side of the garage will make drainage away from that area more
circuitous and the ground adjacent to the foundation could he flatter than 5%. Eliminating
the berm would alleviate that problem. It probably would be clearer to have more detail
on the plan for what the proposed slopes are directly adjacent to the house. Two lawn
drains are proposed between the driveway anti the front entry arca of the house. I assume
that these drains are piped to daylight on the slope below the house to the west. The slope
of the landscape area to these drains is not defined. A drywell is proposed in the lawn
area below the boulder covered slope south of the house. There is some question as to
whether this drywell is needed. The design of the drywell should be verified for the
Gruenefeldt Construction
August 14, 2013
Page 2
amount of calculated runoff. The slope of the lawn in the area west of the drywell is not
defined on the plan but, based on the contours, appears to be about 21/2% down to the west
steepening to about 3% near the top of the 20 percent slope west of the house.
Overall, the grading plan appears adequate with some further definition of the. slopes in
landscape areas directly adjacent to the house.
If you have any questions or need further assistance, please call our office.
Sincerely,
HEPWORTH — PAWLAK GEOTCHNICAL, INC.
,O_.001uIII 11111
a 4�S
1i0 2444$:
Daniel E. Hardin, P.E
%IN " ft 7A
Rev. by: SLP y,'`e �*..«,..,c, ,&o
PO NAL tacIr
DEH/ksw
Job No, 112 397A
GLI -Titch