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HEPWORTH-PAWLAK GEOTECHNIC/IL
December 31, 2013
Resort Development Building
Attn: Chance & Pam Soldoff
493 Holland Hills Road
Basalt, Colorado 81621
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Job No.113 464A
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 49, Elk
Springs (aka Los Amigos), Elfin Place, Garfield County, Colorado
Dear Mr. & Mrs. Soldoff:
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 yon dated December 12, 2013. The
data obtained and our recommendations based on the proposed construction and
subsurface conditions encountered are presented in this report.
Proposed Construction: The proposed residence will be a two story wood frame
strncture over a crawlspace with an attached garage located on the site as shown on
Figure I. Garage floor will be slab-on-grade. Cut depths are expected to range between
about 3 to 5 feet. Foundation loadings are assumed to be relatively light and typical of
the proposed type of constrnction.
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 slopes strongly down to the east at about I 0% grade.
Vegetation on the site consists of pin on and juniper trees with an understory of grass and
weeds. There was about a foot of snow on the site at the time of our field work.
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavating 2 exploratory pits at the approximate locations shown on Figure I. The logs
of the pits are presented on Figure 2. The subsoils encountered, below about I Yi feet of
topsoil, consist of I Yi to 2Yi feet of sandy silty clay with basalt rocks overlying highly
calcareous sandy silt and clay with scattered to frequent basalt rocks from cobble to
boulder size. Refusal to backhoe digging was encountered at 4 to 6 feet deep due to the
presence of basalt rocks in highly calcareous matrix soils. Atterberg Limits testing
-2-
indicates that the sandy clay and silt soils have medium plasticity. The laboratory test
results are summarized in Table 1. 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 psffor support of the proposed residence. The soils tend to compress
after wetting and there could be on the order of 1 inch of post-construction foundation
settlement. Footings should be a minimum width of 18 inches for continuous walls and 2
feet for columns. Loose and disturbed soils and existing topsoil encountered at the
foundation bearing level within the excavation silould be removed. The exposed soils at
footing bearing level should then be moistened and compacted. 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 I 0 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.
We should observe the completed building excavation for further bearing soil evaluation.
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 experierice and the intended
slab use. A minimum 4 inch layer of free-draining gravel should be placed beneath slabs
to act as a leveling course. 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 mountainous areas 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
Job No.113 464A
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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 of2 inches. The
drain gravel backfill should be at least 1 ~ feet deep.
Surface Drainage: Keeping the bearing soils dry is important to preventing potential
foundation movement and building distress. The following drainage precautions should
be observed during construction and maintained at all times after the residence has been
completed:
1)
2)
3)
4)
Inundation of the foundation excavations and underslab areas should be
avoided during construction.
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.
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.
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 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
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 techoical interpretations by others of our information. As the
project evolves, we should provide continued consultation and field services during
Job No.113 464A
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construction to review and monitor the implementation of our recommendations, and to
verify that the reconunendations have been appropriately inte1preted. 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
engmeer.
If you have any questions or if we may be offinther assistance, please let us know.
Respectfully Submitted,
HEPWORTH -PAWLAK GEOTECHNICAL, INC.
Daniel E. Hardin, P .E.
Rev. by: SLP
DEH/ksw
attachments Figure 1 -Location of Exploratory Pits
Figure 2 -Logs of Exploratory Pits
Table 1 -Summary of Laboratory Test Results
Job No. I I 3464A
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APPROXIMATE SCALE
1' = 80'
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113 464A ~ LOCATION OF EXPLORATORY PITS
He wortA-Pawlck Geoteohnli:al
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Figure 1
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0
PIT 1
0
5
-, WC=16.1
~ -200=89
_ j WC=7.2
-200=29
Ll=39
Pl=13
PIT 2
10
LEGEND:
TOPSOIL; organic sandy clay with basalt cobbles and boulders, firm, moist, dark brown.
CLAY (CL); sandy, silty, with basalt cobbles and boulders, slightly moist, brown to gray-brown.
SILT AND CLAY (ML-CL); sandy, with basalt cobbles and boulders, stiff, slightly moist, calcareous.
2" Diameter hand driven liner sample.
Disturbed bulk sample.
T Practical digging refusal on basalt rocks and highly calcareous matrix soil ..
NOTES:
1. Exploratory pits were excavated on December 13, 2013 with a mini-excavator.
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 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.
0
5
10
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 (%)
-200 = Percent passing No. 200 sieve
LL = Liquid Limit (%)
Pl = Plasticity Index (%)
113 464A GO'~
HEPW01tr1-l·PAWLAK GEOTECHNICAl.
LOGS OF EXPLORATORY PITS Figure 2
HEPWORTH-PAWLAK GEOTECHNJCAL, INC.
TABLE 1 Job No.113464A
SUMMARY OF LABORATORY TEST RES UL TS
SAMPLE LOCATION NATURAL GRADATION AITERBERG LIMITS UNCONFINED
MOISTURE NATURAL PERCENT COMPRESSIVE DRY DENS11'Y GRAVEL SAND PLASTIC SOJLOR PIT DEPTH CONTENT PASSING NO. LIQUID LIMIT INDEX STRENGTH BEDROCK 1YPE {%) {%) 200SJEVE
(ft) {%) {pcf) {%) {%) {PSF)
1 2 16.1 89 Sandy Silty Clay
5 7.2 29 39 13 Highly Calcareous Silt and
Clay