HomeMy WebLinkAboutSubsoil Study for Foundation Design 10.31.05{ .
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:;EPWO?.TH ·PAWLAK GEOTECHNICAL
SUBSOIL STlJDY
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FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 3, FOUR MILE RA ... NCH
RED CLIFF CIRCLE
GARFIELD COUNTY, COLOR.WO
JOB NO. 105 772
OCTOBER 31, 2005
PREPARED FOR:
IMAGE CONSTRUCTION
ATTN:ABDIPIRZADEH
1901 COLOR0\\1 ROAD
GLEN"'OOD SPRINGS, COLORWO 81601
Parler 303-841·7119 • Colorndu Srri11gs i 19-633-5562 • Silverchonw ·170 46S-J o.O::,C)
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY ............................................................................ -1 -
PROPOSED CONSTRUCTION ..................................................................................... -1 -
SITE CONDITJONS ....................................................................................................... -2 -
SUBSIDENCE POTE1\1TIAL ......................................................................................... -2 -
FIELD EXPLORATION ................................................................................................. -2 -
SUBSURFACE CONDITIONS ...................................................................................... -3 -
FOlJNDATION BEARING CONDffiONS ................................................................... -4 -
DESIGN RECOMMENDAT IONS ................................................................................. -4-
FOUND . .i\ TIONS ........................................................................................................ - 4 -
FLOOR SL.ABS················~··································································· ............................ -5 -
SURFACE DRAINAGE ............................................................................................. -6-
( LIMITATIONS ............................................................................................................... - 6 -
FIGURE I -LOCATION OF EXPLORATORY BORINGS
FIGURE 2 -LOGS OF EXPLORATORY BORINGS
FIGUJlE 3 -LEGEND AND NOTES
FIG URE S 4 and 5-SWELL-CONSOLIDATION TEST RESULTS
TABLE I-SUMMARY OF LABORATORYTESTRESULTS
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PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located
on Lot 3, Four Mile Rnnch , Red CJiff Circle, Garfield County, Colorado. The project site
is shown on Figure I. 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 Image Construction dated August 30, :wos.
A field exploration program consisting of exploratory borings was conducted to obtain
infonnation on the subsurface conditions. Samples of the subsoils obtained during the
field exploration were tested in the Jaboratory to detennine 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.
nus report summarizes the data obtained during this study and presents our conclusions,
design recommendations and other geotechnicaJ 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 with an attached garage.
Ground floor will be either structural over a crawlspace or slab-on-grade. Grading for the
structure is assumed to be relative)y minor with cut depths between about 3 to 4 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.
Job No I 05 772
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SITE CONDITIONS
The site was vacant at the time of our field exploration. The ground surface on the lot is
relatively flat with a gentle slope down to the west-southwest. An existing pond is
located on the western portion of the lot. Vegetation consists of grass and weeds. Some
"pit run" filJ had been placed near Red Cliff CircJe for the proposed shared driveway with
Lot2.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the
Four Mile Ranch development. These rocks are a sequence of gypsiferous shale, fine-
grained sandstone/siltstone and limestone with some massive beds of gypsum. There is a
possibility that massive gypsum deposits associated with the fagle Valley Evaporite
underlie portions of the lot. Dissolution of the gypsum under certain conditions can -.:ause
sinkholes to develop and can produce areas of localized subsidence. Sinkholes were not
observed in the immediate area of the subject Jot. No evidence of cavities was
encountered in the subsurface materials; however, the exploratory borings were relatively
shallow, for foundation design only. Based on our present knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The
risk of future ground subsidence on Lot 3 throughout the service life of the proposed
residence, in our opinion, is low; however, the owner should be made aware of the
potential for sinkhole development. If further investigation of possible cavities in the
bedrock beJow the site is desired, we should be contacted.
FIELD E>..'PLORA TION
The field exploration for the project was conducted on September 19, 2005. Two
exploratory borings were drilled at the locations shown on Figure 1 to evaluate the
subsurface conditions. The borings were advanced with 4 inch diameter continuous flight
Job No . toS 77'1.
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augers powered by a truck-mounted CME-458 drill rig. The borings were Jogged by a
representative of Hepworth-Pawlak Geotechnical, Inc .
Samples of the subsoils were taken with HH inch and 2inch1.D. spoon samplers. The
samplers were driven into the subsoils at various depths with blows from a 140 pound
hanuner 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 ofExplQratory Borings,
Figure 2. The samples were returned to our laboratory for review by the project engineer
and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.
The subsoils consist of about~ foot of topsoil overlying stiff to very stiff, sandy silt_v
clay . Basalt gravel, cobbles and boulders in a sandy silt matrix was encountered beneath
the clay at depths of 1 7 feet and 25 feet.
Laboratory testing performed on samples obtained from the borings included natural
moisture content, density and finer than sand size gradation analysis. Results of swell-
consolidation testing perfonned on relatively tmdisturbed drive samples of the clay soils,
presented on Figures 4 and 5, generally indicate low compressibility under existing
moisture conditions and light loading and moderate to high compressibility upon
increased loading after wetting. The sample from Boring 2 at 3 feet showed a minor
expansion potential when wetted under a light surcharge. The sample from Boring 2 at
10 feet showed a minor collapse potential (settlement under constant load) when wetted.
The laboratory testing is summarized on Table 1.
Job No 105 772
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Gro undwater was measured in Boring 2 at a depth of 15 1 : feet. No :free water was
encountered in Boring 1 at the time of drilling or when checked 8 days later. The
subsoi ls were slightly moist to wet below groundwater.
FOUNDATION BEARING CONDITIONS
Some of the clay subsoils encountered in Fo ur Mile Ranch possess an expansion 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.
DESIGN RECOMI\1.E1'TDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the
nature of the proposed construction, we reconunend the building be founded with spread
footings bearing on the natural subsoils.
The design and construction criteria presented below should be obsen1 ed for a spread
footi ng foundation system.
1) Footings p laced on the undisturbed natural subsoils should be designed for
an allowable bearing pressure of 1 ,500 ps[ 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 additionaJ
movement if the subgrade becomes wetted.
2) The footings should have a minimum width of 16 inches for continuous
walls and 2 feet fo r isolated pads.
3) Exterior footings and footings beneath unheated areas should be provided
( w ith adequate soil cover above their bearing elevation for frost protection.
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Placement of foundations at least 3 6 inches below 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 12
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 55 pcf.
5) The topsoil and any loose or disturbed soils should he removed and the
footing bearing level extended down to the finn natural soils. The exposed
soils in footing area should then be moistened and compacted.
6) A representative of the geotechnical engineer should observe alJ footing
excavations prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly lo<rled slab-
on-grade construction. The clay soils have variable settlement/heave potential which
should be further evaluated 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 aUow 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 offree-
draining gravel should be placed beneath slabs-on-grade to facilitate drrunage and limit
capilJary moisture rise. This material should consist of minus 2 inch aggregite with at
least 50% retained on the No. 4 sieve and less than 2°·o passing the No. 200 sieve.
AH 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. Require:l fill can
consist of the on-site soils or suitable imported fill devoid of vegetation, topsoil and
oversized rock.
Job No 105 772
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SURFACE DR.A..INAGE
The following drainage precautions shoutd be observed during construction and
maintained at all times after the residence has been completed:
1) Inundation of the foundation excavations and undersJab 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 fowidation 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 1 0 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 )east 5 feet from foundation
walls.
LIMITATIONS
lb.is study has been conducted in accordance with generally accepted geotechnicaJ
engineering principles and practices in this area at this time. We make no warranty either
express or implied. The conc]usions and recommendations submitted in this report are
based upon the data obtained from the exploratory borings drilled at the locations
indicated on Figure t: 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
consu1ted. Our findings include interpo]ation and extrapolation of the subsurface
Job No . IOS 772
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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 infonnation. As the
project evolves, we should provide continued consultation and field senrices during
construction to review and monitor the implementation of our recommendations, and to
verify that the reconunendations have been appropriately interpreted. Significant desil!Il
changes may require additional analysis or modifications to the reconunendations
presented herein. We recommend on-site observation of excavations and foundation
bearing strata and testing of structural fill by a representative of the geotcclmical
en~rineer.
Respectfully Submitted,
HEPWORTH -PAWLAK GEOTECHNlCAL, INC.
Jordy Z. Adamson, Jr., P .E .
Reviewed by:
Daniel E. Hardin, P.E.
JZA/djb
Job No I OS 772
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105 772
LOT2
HPGEOTECH
JOB NO. 105 n1
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BORING2 I I
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APPROXIMATE SCALE
1" = 100
LOT4
-TRAIL AND BIKE PATH -
LOCATION OF EXPLORATORY BORINGS Figure 1
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90
85
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75
70
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105 772
BORING 1
ELEV .= 91.5 '
16112
21/12
WC •7.9
00s 92
-200 •75
21/12
16/12
50/6
BOAING2
ELEV.= 90.6'
14/12
wc-11 .1
00s 93
17/12
T 14/12
wc-1.s
00=93
8 10/12
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6/12
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Note: Explanation of symbols is shown on Figure 3.
LOGS OF EXPLORATORY BORINGS
95
90
85
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75
70
65
Figure 2
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LEGEND:
§ TOPSOIL; sandy silly clay, organic , firm, slightly moist. brown.
0 CLAY (CL}, silty sandy, stiff to very stiff , medium stiff in Boring 2 with depth, slightly moisl lo wet below
groundwater in Boring 2, brown, slightly calcareous and porous , scattered grave l and cobbtes.
~ BASALT GRAVEL, COBBLES AND BOULDERS (GM); in a sandy silt matrix, dense, slightly moist, brown
p
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16/12
0,8
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Re lat ively undisturbed drive sample; 2-inch f.D. California liner sample.
Drive sample; standard penetralion test (SP1), 1 3/8inch 1.0. spm spoon sample, ASTM 0-1586.
Drive sample blow count; Indicates that 16 blows of a 140 pound hammer falling 30 inches were
tequired to drive the California or SPT sampler 12 inches .
Free water level in boring and number of days following drilling measurement was taken.
Depth at which boring had caved when measured on September 27, 2006
T Pfactical drilling refusal. Where shown above bottom of log indicates that multiple attempts were made to
advance the boring.
NOTES:
1. Exploratory borings were drilled on September 19. 2005 with 4-lnch diameter continuous flight power auger.
2. Locations of exploratory borings were measured approximately by pacing from features shown on lhe sile plan
provided.
3. Elevations or exploratory borings were measured by instrument level aod refer to the Bench Mark shown on Figure 1.
4. The exploratory boring locations and elevations should be considered accu rate only to the degree implied by the
method used.
5. The lines between materials shown on the exploratory bor ing logs represent the apptoximate boundaries between
material types and transitions may be gradual.
6. Water level readings shown on lhe logs were made at the time and under the conditions Indicated. Ffucluations In
water level may occur with time.
7. Laboratory Testing Rest~s:
WC == Water Content (
DD = Dry Density (pc~
-200 = Percent passing No. 200 sieve
105 7i2 LEGEND AND NOTES Figure 3
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Moisture Contenl "" 7.9 percent
Ory Density :: 92 pcf
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Sample of. Sandy Silty Clay
From : Bor1119 1 at 5 Feet
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Cl) 1 C1> a \ ~ E ~ 0 u 2 ~ ...., )
Nd movement
upon
wetting
0.1 1.0 10 100
APPLIED PRESSURE • ksf
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Moisture Content = 11 .7 percent r--lj r-. ~ \ Dry Density = 93 pcf
1 r--...._
~, ~ Sample of: Sandy Silty Clay
.... , From: Boring 2 at 3 Feet
2
fl.
Expansion
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3 wetting
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0.1 1.0 10 100
APPLIED PRESSURE -ksf
105 772 ~ SWELL·CONSOLIDATION TEST RESULTS Figure 4
H-worth-Powlall Ceolechnlcol
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( Moisture Content = 7.5 percent
Oiy Density = 93 pcf
Sample of : Sandy Silty Clay
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From : Soring 2 at 1 o Feet
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Compression
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wetting
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APPLIED PRESSURE -ksl
105 772 ~~ SWELL-CONSOLlDATION TEST RESULTS Figure 5
H1111worth-Pawlok Geolechnlcal
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TABLE 1 Job No. 105 772 . ·--SUMMARY OF IJ\BORATORY TEST RESULTS
SAMPLE LOCATION NATURAL NATURAL GRADATION PERCENT ATTERBERG LIMITS UNCONANEO
MOlsnJRE ORY GRAVEL SAND PASSING LIQUID Plf\STIC COMPRESSIVE SOIL OR BORING DEPTH CONTENT DENSrtY NO. 200 LIMIT INDEX STRENGTli BEDROCK TYPE (%) (%) SIEVE cm (%) cocn ('li.) (%} (PSFl
l 5 7.9 92 75 Snndy Silty Clay
2 3 11.7 93 Sandy Silty Clay
10 7.5 93 Sandy Silty Clay