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HEPWORTH - PAWLAI< GEOTECI 1 NICAL
May 30, 2006
Peter Toborek
P. 0. Box 2962
Basalt, Colorado 81621
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Job No.106 0386
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 7, Filing 6,
Elk Springs Subdivision, 0488 Wood Nymph Lane, Garfield County,
Colorado
Dear Mr. Toborek:
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 April 28, 2006. The data
obtained and our recommendations based on the proposed construction and subsurface
conditions encountered are presented in this report. Hepworth-Pawlak Geotechnical, Inc.,
previously performed a preliminary geotechnical study for Filings 6 through 9, Elk
Springs (formerly Los Amigos Ranch PUD) and presented our findings in a report dated
February 14, 1997, Job No. 197 617.
Proposed Construction: The proposed residence plans are conceptual and we
understand that our findings will be considered in the purchase of the lot. Typical
construction in the area consists of one and two story log or wood frame construction
above a basement, crawlspace or slab -on -grade floor with an attached garage. The site is
shown on Figure 1. Ground floors could be slab -on -grade or structural above crawlspace.
Cut depths are expected to range between about 2 to 8 feet. Foundation loadings for this
type of construction are assumed to be relatively light and typical of the assumed type of
construction.
If building 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 site is located on a rolling upland mesa on the east side of the
lower Roaring Fork River Valley. Vegetation consists of grass and weeds with some sage
brush in the front part of the lot. The ground surface slope is moderate down to the
southwest. There is about 7 feet of elevation difference across the building envelope.
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavating four exploratory pits at the approximate Locations shown on Figure 1. Pits 3
and 4 were excavated to evaluate the subsoil conditions for utility trenches. The logs of
the pits are presented on Figure 2. The subsoils encountered, below about one foot of
topsoil, consist of one to two feet of sandy silty clay overlying basalt cobbles and
11,11"1c•a'r 3C3-841-7119 Ltlltlliitit1 Splings 719-633-5i62 /s Sil1'eirhtll'ni.' 970 468 19t6Q
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boulders in a sand clay and silt matrix. Gravelly silty to very silty sand was encountered
in Pit 1 from 3 to 6 % feet. Results of swell -consolidation testing performed on a
relatively undisturbed sample of the sandy clay soils, presented on Figure 3, indicate low
to moderate compressibility under conditions of loading and when wetted. 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 soil designed for an allowable soil bearing
pressure of 1,500 psf for support of the proposed residence. The clay and sand soils tend
to compress after wetting and there could be about 1 inch or more of post -construction
foundation settlement. Footings placed entirely on the basalt rock soils can be designed
for an allowable bearing pressure of 2,500 psf and should have relatively low settlement
potential. Footings should be a minimum width of 16 inches for continuous walls and 2
feet for columns. Utility trenches and deep cut areas may require rock excavating
techniques such as chipping or blasting. Loose and disturbed soils encountered at the
foundation bearing level within the excavation should be removed and the footing bearing
level extended down to the undisturbed natural soils. Voids created from boulder
removal at footing grade should be filled with a structural material such as road base
compacted to at least 95 percent of standard Proctor density at a moisture content near
optimum. 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. 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 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 soils 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
Job No. t 06 0386
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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.
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 1'/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 ofthe 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. A swale will be needed uphill to direct surface runoff
around the residence.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation and lawn sprinkler
heads should be located at least 5 feet from the building. Consideration
should be given to the use ofxeriscape to limit potential wetting of soils
below the foundation 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 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. 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 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
Job No.106 0386
Gggtech
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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.
'Louis E. ElIer
Reviewed by:
Steven L. Pawlak, P.
LEE/ksw
15222Vgah 04;
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FOFI:
attachments Figure 1 - La xploratory Pits
Figure 2 Logs of Exploratory Pits
Figure 3 -- Swell -Consolidation Test Results
cc: Chris Striefel
Job No.106 [)386
GecDtech
LOT 6
•
PIT 4
APPROXIMATE SCALE
1"=80'
WOOD NYMPH AOgD
r--
PIT2
BUILDING
ENVELOPE
_
PIT1
LOT 7
FILING 6
106 0386
OPEN SPACE
HEPWORTH•PAWLAK GEOTECHNICAL.
•
PIT 3
LOCATION OF EXPLORATORY PITS
LOT 8
Figure 1
0
10
LEGEND_
N
1/1
T
PIT 1
WC=21.8
DD=92
PIT 2
PIT 3
PIT 4
10
TOPSOIL; sandy silt and clay, organic, moist, dark brown_
CLAY (CL); sandy, silty, stiff, slightly moist to moist, reddish brown.
SAND (SM): gravelly, silty to very silty, medium dense, slightly moist to moist, light brown to while, calcareous.
BASALT COBBLES AND BOULDERS (GM); in a sandy clay and sit matrix, medium dense, sEghtly moist, light
brown 1.0 white, calcareous.
2' Diameter hand driven liner sample.
Practical digging refusal with backhoe.
NOTES:
1. Exploratory pats were excavated on May 10, 2006 with a Cat 420D 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 not measured and the logs of exploratory pits are drawn to depth.
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 Eme.
7. Laboratory Testing Results:
WC = Water Content (%)
DD = Dry Density (pcf)
-200 = Percent passing No. 200 sieve
106 0386
HEPWORTH•PAWLAtc GEOTECHNICAL.
LOGS OF EXPLORATORY PITS
Figure 2
Compression %
0
1
2
3
Moisture Content 21.8 percent
Dry Density = 92 pcf
Sample of: Sandy Clay
From: Pit 1 at 2 Feet
No movement
upon
wetting
0.1
106 0386
H
1.0
HEPWORTH•PAWLAK GEOTECHNICAL
10 100
APPLIED PRESSURE - ksf
SWELL -CONSOLIDATION TEST RESULTS
Figure 3