HomeMy WebLinkAboutSoils Report 07.15.2016H -PKU MAR
Geotechnical Engineering 1 Engineering Geology
Materials Testing 1 Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 23, SUN MEADOW ESTATES
SOUTH MEADOW DRIVE
GARFIELD COUNTY
COLORADO
JOB NO. 16-7-137
JULY 15, 2016
PREPARED FOR:
CHUCK SAKYS
3450 ENDURO ORIN'' E
LAKE HAVASU CITY, AZ 86404
chucksakys@gmail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - I -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
FIELD EXPLORATION _
SUBSURFACE CONDITIONS ........................ .... en. ...... ....F .; p • aa..,+LEL 3 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS - 4 -
FLOOR SLABS ..... ...
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAIN AGE
LIM !TA' r ION S - 7 -
FIGURE I - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3- LEGEND AND NOTES
FIGURES 4 AND 5- SWELL -CONSOLIDATION TEST RESULTS
TABLE 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 23, Sun Meadow Estates, South Meadow 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 agreement for professional services to Chuck Sakys dated June 22, 2015. We
previously performed a preliminary geotechnical study for the Sun Meadows Estates
development and presented our findings in a report dated March 28, 2000,
Job No. 100 169
A field exploration program consisting of exploratory borings was conducted to obtain
information on the 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 design of the residence has yet to be determined. The residence will probably be a
one to two story wood frame structure located on the Iot as shown on Figure 1. Ground
floors may be structurally supported over crawlspace and/or slab -on -grade, depending on
the findings of our study. Grading for the structure is expected 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.
When building location, grading and loading information have been developed, we
should be notified to re-evaluate the recommendations presented in this report.
SITE CONDITIONS
The lot was vacant at the time of our field exploration and the ground surface appeared
mostly natural. The terrain is moderately sloping down to the east. Along the east side of
the lot the slope becomes steeper down to a dry gulley farther to the east. Elevation
difference across the proposed building site is estimated at about 3 to 5 feet. Vegetation
consists of grass and weeds.
FIELD EXPLORATION
The field exploration for the project was conducted on June 29, 2016. Two exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface
conditions. The borings were drilled at the locations based on the proposed footprint of
the house as marked by stakes set in the field by the client. The borings were advanced
with 4 -inch diameter continuous flight augers powered by a truck -mounted CME -4513
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. 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 Iaboratory for review by the project engineer and testing.
H -P== KUMAR
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SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.
The subsoils encountered, below about 1 foot of organic topsoil, consisted of about 13 to
15 feet of stiff to very stiff, sandy silt overlying medium dense, silty to very silty sand
that extended down to the maximum depths drilled of 31 feet. The sandy silt and silty to
very silty sand soils were typically clayey.
Laboratory testing performed on samples obtained from the borings included natural
moisture content and density, and percent finer than sand size gradation analyses. Results
of swell -consolidation testing performed on relatively undisturbed drive samples,
presented on Figures 4 and 5, indicate generally low compressibility under conditions of
natural moisture content and light loading. The samples typically showed a low collapse
potential when wetted under a constant light surcharge and moderate compressibility
when loaded after wetting. One sample (Boring 1 at 15 feet) showed minor swell
potential when wetted. The samples showed generally moderate compressibility when
loaded after wetting. The laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist with depth.
FOUNDATION BEARING CONDITIONS
The soils encountered at the building site have low bearing capacity and low to moderate
settlement potential when wetted. Shallow spread footings placed on these soils can be
used for foundation support with a risk of settlement. The risk of settlement is primarily
if the bearing soils become wetted. Spread footings bearing on a depth of compacted
structural fill (typically 3 to 4 feet of re -worked on-site soils) is commonly used to reduce
the risk of settlement in the area. The swell potential encountered in one of the samples k
minor and can be neglected in the foundation (and floor slab) design.
H -P< KUMAR
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A micro -pile or helical pier foundation system could also be used to provide a relatively
low risk of building settlement and distress but will need to extend down into low
compressibility sand and gravel with cobble soils or bedrock.
Provided below are recommendations for a spread footing foundation system bearing on
the natural soils. If recommendations for spread footings bearing on structural fill a
micro -pile or helical pier foundation system are desired, we should be contacted. A deep
boring would be needed for the pile or pier foundation design.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the
nature of the proposed construction, we believe the building can be founded with spread
footings bearing on the natural soils or on properly placed and compacted structural fill
with some risk of settlement. Precautions should be taken to prevent wetting of the
bearing soils.
The design and construction criteria presented below should be observed for a spread
footing foundation system.
1) Footings placed on the natural soils or a depth of compacted structural fill
should be designed for an allowable bearing pressure of 1,500 psf. Based
on experience, we expect initial settlement of footings designed and
constructed as discussed in this section will be about 1 inch or less. There
could be additional settlement if the bearing soils were to become wetted.
The magnitude of the settlement would depend on the bearing conditions
and depth and extent of the wetting but may be on the order of 1 to 11/2
inches for a limited depth of wetting on the order of 15 feet.
2) The footings should have a minimum width of 18 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.
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Placement of foundations at least 36 inches below exterior grade is
typically used in this area.
4) Continuous foundation walls should be heavily reinforced top and bottom
to span local anomalies and better withstand the effects of some
differential settlement such as by assuming an unsupported length of at
least 14 feet. Foundation walls acting as retaining structures should also
be designed to resist a lateral earth pressure corresponding to an equivalent
fluid unit weight of at least 50 pcf.
5) All topsoil should be removed in the footing areas and the exposed
subgrade scarified, moistened to near optimum and compacted. Structural
fill placed below footing areas should consist of the on-site soils, or a
suitable well graded imported granular material such as road base,
compacted to at least 987o standard Proctor density at a moisture content
within about 2% of optimum.
6) A representative of the geotechnical engineer should observe all footing
excavations and observe placement and test structural fill compaction on a
regular basis prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab -
on -grade construction with a risk of settlement mainly if the subgrade soils become
wetted as discussed above. Providing a depth (2 to 3 feet of re -worked on-site compacted
soils) below the slabs could be done to reduce the risk of settlement and slab distress. We
should review the need for structural fill below floor slabs at the time of 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
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4 -inch layer of road base should be placed immediately below floor slabs for support and
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 12% 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 topsoil and oversized (plus 6 inch) rocks.
UNDERDRAIN SYSTEM
A perimeter foundation drain system around shallow crawlspace areas (less than 4 feet
deep) or around floor slab -at grade areas such as the garage should not be needed
provided positive surface drainage is provided away from foundation walls and the
foundation wall backfill is adequately compacted. If a basement level is planned, a
perimeter foundation drain system will be needed.
SURFACE DRAINAGE
Positive surface drainage is an important aspect of the project to prevent wetting of the
bearing materials. It will be critical to the building performance to keep the bearing soils
dry. 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.
3) The ground surface surrounding the exterior of the building should be
sloped to drain away from the foundation in all directions. We
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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.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
51 Landscaping which requires regular heavy irrigation should be located at
least 10 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.
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
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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,
H-P�KUMAR
..4/22Ak 11/idA
Shane M. Mello, Staff Engineer
Reviewed by:
David A. Young, P.
SMM/ksw
LOT 24
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16-7-137
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LOCATION OF EXPLORATORY BORINGS
Figure 1
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5
- 10
15
20
25
30
BORING 1 BORING 2
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s
- 26/12
WC 53
DD 102
1212
WC 66
DD 100
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is WC 51
DD 115
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r.'•' WC=12.8
DD=112
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/1 25/12
80
200 WC- 70
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DD 93
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- 47/12
1 - 24/12
WC 71
DD 101
r' 25/12
WC=9 2
DD 116
35:12
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17/12
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5
10
15
20
25
30
35 35
Note: Explanation of symbols is shown on Figure 3
Depth - Feet
16-7-137
H --P ICUMAR
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LOGS OF EXPLORATORY BORINGS
Figure 2
LEGEND:
TOPSOIL; sandy silt and c'ay with organics, medium stiff, slightly moist, dark brown.
SILT (ML); sandy to very sandy, typically clayey, stiff to very stiff, slight -y most, light brown.
SAND (SM -SC); silty to occasionally very silty, typically clayey, med um dense, slightly moist to moist, brown
Relatively and sturbed drive sample; 2 -inch I.D. Californ a liner sample
32/12 Drive sample bow count; indicates that 32 blows of a 140 pound hammer falling 30 inches were
required to drive the Californ a sampler 12 inches.
NOTES:
1. Exploratory borings were drilled on June 29, 2016 with 4 -inch diameter continuous flight power auger.
2. Locations of exploratory borings were measured approx mately by pacing from features shown on the site plan
provided.
3. Elevations of exploratory borings were not measured and the logs of exploratory borings are drawn to depth.
4. The exploratory boring locations 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. 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
16-7-137
H -P KUMAR
LEGEND AND NOTES
Figure 3
Compression %
ompression - ;: xpansion %
0
1
2
3
1
0
1
2
Moisture Content 5.3 percent
Dry Density 102 pcf
Sample of: Sandy Clayey Silt
From: Boring 1 at 5 Feet
Compression
upon
- wetting
0.1
1.0 10
APPLIED PRESSURE - ksf
100
Moisture Content — 5 1 percent
Dry Density --- 115 pcf
Samp e of: Sandy Clayey Silt
From: Boring 1 at 15 Feet
Expansion
upon
wetting
0.1
1.0 10
APPLIED PRESSURE - ksf
100
16-7-137
H-PKUMAR
r.;
SWELL -CONSOLIDATION TEST RESULTS
Figure 4
Compression %
Compression %
0
2
3
4
5
6
0
1
3
4
Moisture Content = 7.1 percent
Dry Density = 101 pcf
Sample of: Very Sandy Clayey Silt
From Boring 2 at 10 Feet
Compression
upon
wetting
0.1
1.0 10
APPLIED PRESSURE - ksf
100
Moisture Content 9.2 percent
Dry Density ~- 116 pct
Sample of: Silty Clayey Sand
From: Boring 2 at 20 Feet
Compression
upon
wetting
0.1
1.0 10
APPLIED PRESSURE - ksf
100
16-7-137
H-Pt-KUMAR
SWELL -CONSOLIDATION TEST RESULTS
Figure 5
Job No. 16-7-137
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Sandy Clayey Silt
Sandy Clayey Silt
Silty Clayey Sand I
Sandy Silt
Very Sandy Clayey Silt II
Silty Clayey Sand
11
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
ATTERBERG LIMITS
PLASTIC
INDEX
(%)
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PERCENT
PASSING
NO. 200
SIEVE
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NATURAL
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