HomeMy WebLinkAboutSoils Report 06.07.2007SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 26, FIRST EAGLE'S POINT
EAGLE RIDGE DRIVE
BATTLEMENT MESA, COLORADO
JOB NO. 107 0356
JUNE 7, 2007
PREPARED FOR:
LANDMARK PROPERTIES
ATTN: BLEU L'ESTRANGE
1001 GLEN OAK LANE
GLENWOOD SPRINGS, COLORADO 81601
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - l -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS - 4 -
FLOOR SLABS - 6 -
UNDERDRA€N SYSTEM - 6 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 7 -
FIGURE l - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1 SUMMARY OF LABORATORY TEST RESULTS
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located
on Lot 26, First Eaglets Point, Eagle Ridge Drive, Battlement Mesa, 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 Landmark Properties dated
May 11, 2007. 1-Iepworth-Pawlak Geotechnical, Inc. previously conducted a preliminary
geotechnical study for development of the subdivision and presented our findings in a
report dated November 21, 2003, Job No. 103 680.
An exploratory boring was drilled on the lot to obtain information on the general
subsurface conditions. Samples of the subsoils 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 two story wood frame structure aver a walkout
basement level. The attached garage and basement floors will be slab -on -grade. Grading
for the structure is assumed to be relatively minor with cut depths between about 3 to 10
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.
lob No. 107 0356
L
SITE CONDITIONS
The site was vacant at the time of our field exploration. There is a pile of excavation
spoils consisting of basalt cobbles and boulders on the lot from the construction of a
residence to the south. There appears to be some minor fill on the lot from overlot
grading as part of the subdivision development. The ground surface is relatively flat with
a gentle to moderate slope down to the west. There is a steeper slope on the north side of
the lot down to the northeast. Vegetation consists of sparse grass and weeds.
FIELD EXPLORATION
The field exploration for the project was conducted on May 23, 2007. One exploratory
boring was drilled at the location shown on Figure 1 to evaluate the subsurface
conditions. The boring was advanced with 4 inch diameter continuous flight augers
powered by a truck -mounted CME -45B drill rig. The boring was 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. Depths at which the samples were taken and the penetration
resistance values are shown on the Log of Exploratory Boring, Figure 2. The samples
were returned to our laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2.
The subsoils consist ofabout ' = foot of topsoil and 3' 3 feet of very stiff, sandy silty clay
with scattered gravel overlying relatively dense, basalt gravel, cobbles and boulders in a
sandy clay matrix, Drilling in the basalt rock soils with auger equipment was difficult
Job Nu. 107 0356
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due to the size and hardness of the basalt rock and drilling refusal was encountered in the
deposit.
Laboratory testing performed on samples obtained from the boring included natural
moisture content and density, finer than sand size gradation analysis and Atterberg limits.
Results of swell -consolidation testing performed on a relatively undisturbed drive sample
of the clay soils, presented on Figure 4, indicate low compressibility under existing Iow
moisture conditions and light loading and a low expansion potential when wetted under a
constant Tight surcharge. Atterberg limits testing performed on a sample of the clay
matrix soils indicate Iow plasticity.
No free water was encountered in the boring at the time of drilling and the subsoils were
slightly moist.
FOUNDATION BEARING CONDITIONS
The clay soils and clay matrix of the rocky subsoils encountered in the First Eagle's Point
development possess variable settlement/heave potential when wetted. Surface runoff,
landscape irrigation, and utility leakage are possible sources of water which could cause
wetting. The settlement/heave potential of the subgrade should be further evaluated at the
time of construction. Bearing on the basalt gravels should provide a relatively low risk of
foundation movement. Shallow footings, such as at the garage, may need to be deepened
to bear below expansive clay. We should review the foundation and grading plans for
adequate setback from the steeper northern slope.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the
nature of the proposed construction. we recommend the building be founded with spread
footings bearing on the natural subsoils.
Job No. 107 035b
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The design and construction criteria presented below should be observed for a spread
footing foundation system.
1) Footings placed on the undisturbed natural subsoils should be designed fo-
an allowable bearing pressure of 2,000 psi. Based on experience, we
expect settlement/heave of footings designed and constructed as discussed
in this section will be about 1 inch or less. There could be some additional
movement of footings if the bearing soils become wetted and could be
differential between footings bearing on the clay and basalt gravel soils.
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 lateral earth pressures as discussed in the "Foundation
and Retaining Walls" section of this report.
5) The topsoil and any loose or disturbed soils should be removed and the
footing bearing level extended down to the natural soils. The exposed
soils in footing area should then be moistened 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 arc
Joh No 107 0356
5
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. Backfill should not contain vegetation, topsoil or oversized rock.
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 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°'o of the maximum
standard Proctor density at a moisture content near optimum. Backfill in pavement and
walkway areas should be compacted to at least 95° o of the maximum standard Proctor
density. Carc 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 backlit!.
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 oldie footings can be
calculated based on a coefficient of friction of 0.35. Passive pressure of compacted
backfill against the sides of the footings can be calculated using an equivalent fluid unit
weight of 300 pcf. 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. Pill placed against the sides of the footings to resist lateral Toads
should be compacted to at least 95% of the maximum standard Proctor density at a
moisture content near optimum.
Jul, Nu 107 0350
6
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -
on -grade construction. The clay soils have variable settlement/heave potential which
could result in somc slab movement if the clay bearing soils become wetted. To reduce
the effects of some differential movement, floor slahs should be separated from all
bearing walls and columns with expansion joints which allow unrestrained venical
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°0 retained on the No. 4 sieve and Tess than 2°0 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 and where clay soils are present that local perched groundwater can
develop during titnes 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, crawispace 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 inven 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 con
tain Tess than 2% passing the No. 200
Joh Na W7 015o Garstech
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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:
1) Inundation of the foundation excavations and undcrslab 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 9000 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.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Irrigation sprinkler heads and landscaping which requires regular heavy
irrigation, such as sod, should be located at least 5 feet from foundation
walls.
6) Surface water should not be concentrated and directed onto the steep slope
to the north without adequate erosion protection.
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 boring drilled at the location 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
!u6 T1u 1117 0356
-8 -
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 extrapolation of the subsurface conditions identified at
the exploratory boring and variations in the subsurface conditions may not become
evident until excavation is performed. I f 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.
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.
lardy Z. Adamson, Jr.,
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Reviewed by:
,fit A Dq,;�s.
Steven L. Pawlak, P.E.
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Sub Nu 107 0356
APPROXIMATE SCALE
1' 30'
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1 I
I 1
1 1
1 LOT 26 1
1 1
1 1 1
1 1 1 1
LOT 25I BORING 11 1 LOT 27
1 • 1
1 1
1 1
1 1
1 1
1 1
L -1
BENCH MARK: GROUND SURFACE.
ELEV. = 100.0% ASSUMED,
EAGLE RIDGE DRIVE
107 0356
LOCATION OF EXPLORATORY BORING Figure 1
Elevation - Feet
BORING 1
ELEV.= 103.3'
105 105
100
95
21/12 _
we=13 r 100 —_,
DD=95
30/12 _
WC=5 4
-200=54
LL=25 —
PI=11 95
90 90
NOTE: Explanation of symbols is shown on Figure 3.
107 0356
HRPWGRT*PAW WS GROTECFR iW.
LOG OF EXPLORATORY BORING
Figure 2
LEGEND:
2 TOPSOIL; sandy silty clay, organics, roots, firm, slightly moist, brown.
CLAY (CL); silty, sandy. scattered gravel, very stilt, slightly moist, Tight brown to white, calcareous.
BASALT GRAVEL AND COBBLES (GC): in a sandy clay matrix, with boulders, dense. slightly moist, light
brown.
r7
r,
li
Relatively undisturbed drive sample; 2 -Inch I.D. California liner sample.
21/12 Drive sample blow count: indicates that 21 blows of a 140 pound hammer falling 30 inches were
required to drive the California sampler 12 inches.
-rPractical drilling refusal. Where shown above bottom of Tog, indicates that multiple attempts were made to
advance the boring.
NOTES:
1. The exploratory boring was drilled on May 23, 2007 with a 4 -inch diameter continuous flight power auger.
2. The exploratory boring location was measured approximately by pacing from features shown on the site plan
provided.
3. The exploratory boring elevation was measured by instrument level and refers to the Bench Mark on Figure 1.
4. The exploratory boring location and elevation should be considered accurate only to the degree implied by the
method used.
5_ The lines between materials shown on the exploratory boring log represent the approximate boundaries between
material types and transitions may be gradual.
6. No free water was encountered In the boring at the time of drilling. Fluctuation In water level may occur with time.
7. Laboratory Testing Results:
WC = Water Content (%)
DD = Dry Density (pct}
-200 = Percent passing No. 200 sieve
LL = Liquid Limit (%)
PI = Pfasticity Index (%)
107 0356
GateCh
HCpwoRT*PAwLAK Gam.
1
LEGEND AND NOTES I Figure 3
Compression - Expansion %
1
0
1
2
3
5
Moisture Content 13.7 percent
Dry Density . 95 pd
Sample of: Sandy Silty Clay
From: Boring 1 at 2 Feet
Expansion
upon
wetting
0.1
1.0
APPLIED PRESSURE kV
10
100
107 0356
HISPWORTMPAWLAK GEwTECNNICAL
SWELL -CONSOLIDATION TEST RESULTS
Figure 4
Job Na. 107 0356
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