HomeMy WebLinkAboutSubsoil Study for Foundation Design 08.22.2016HPKUMAR
Geotechnical Eng nearing! Engineenng Geo o95
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 Silverthome, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
NEAR 2980 COUNTY ROAD 311
GARFIELD COUNTY, COLORADO
PROJECT NO. 16-7-308
AUGUST 22, 2016
PREPARED FOR:
SHANE SMITH
4023 HIGHWAY 103
IDAHO SPRINGS, CO 80452
eik5x6x6 @ hughes.net)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY+- 1 -
PROPOSED CONSTRUCTION - I -
SIT.~ CONDITIONS+. - 1-
FIELD EXPLORATION- 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATION - 3 -
FOUNDATIOAND RETAINING WALLS - 4 -
FLOOR SLABS - 6 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE.,. - 7 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOC OF EXPLORATORY BORING
FIGURE 3 - SWELL -CONSOLIDATION TEST RESULTS
FIGURE 4 - GRADATION TEST RESULTS
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
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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
near 2980 County Road 311, 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 geotechnical
engineering services to Shane Smith dated August 9, 2016.
A field exploration program consisting of an exploratory boring 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 proposed residence will be a single story structure. Ground floor will be structural
over a crawlspace. Grading for the structure is assumed to be relatively minor with cut
depths between about 2 to 3 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.
SITE CONDITIONS
The lot was vacant of permanent structures at the time of our field exploration. There
was construction equipment, shipping containers and a camper on-site. The ground
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surface was gently sloping down to the west in the proposed build area with an elevation
change of about 1 foot. The site was accessed via a dirt trail from County Road 31 I over
a culvert of an active ditch. The ditch was on the eastern portion of the lot running to the
north. Divide Creek meanders along the western side of the lot running to the north.
Vegetation consisted of grass and weeds with scattered shrubs and trees.
FIELD EXPLORATION
The field exploration for the project was conducted on August 10, 2016. One exploratory
borings 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 H-P/Kumar.
Samples of the subsoils were taken with 1% inch and 2 inch I.D. spoon samplers. The
samplers were 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 of about 2 feet of topsoil overlying about 3' feet of medium stiff,
sandy to very sandy clay and silt underlain by about 21/2 feet of loose silty sand. Dense
silty gravel and sand with cobbles and possible small boulders was encountered below a
depth of 8 feet down to the maximum drilled depth of 16 feet. Drilling in the dense
granular soils with auger equipment was difficult due to the cobbles and boulders.
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Laboratory testing performed on samples obtained from the boring included natural
moisture content and density, and gradation analyses. Results of swell -consolidation
testing performed on relatively undisturbed drive samples, presented on Figure 3, indicate
low to moderate compressibility under conditions of loading and wetting. Results of
gradation analyses performed on• a small diameter drive sample (minus 11/2 inch fraction)
of the coarse granular subsoils are shown on Figure 4. The laboratory testing is
summarized in Table 1.
Free water was encountered in the boring at the time of drilling at a depth of about 5'
feet and the upper soils were moist to very moist with depth.
FOUNDATION BEARING CONDITIONS
The upper clay and silt soils have low bearing capacity and low to moderate
compressibility under light loading. Shallow spread footings placed on the upper natural
soils can be used for the building support with a risk of settlement as described below.
The building excavation should be kept shallow to help Iimit moisture problems from the
shallow groundwater level.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the
nature of the proposed construction, the building can be founded with spread footings
bearing on the upper natural soils with a settlement potential. Placing the foundation on
the underlying gravel soils such as with helical piers could be used to limit the settlement
potential.
The design and construction criteria presented below should be observed for a spread
footing foundation system.
1) Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of 1,000 psf. Based on experience, we expect
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settlement of footings designed and constructed as discussed in this section
will be about 1 inch or less.
2) The footings should have a minimum width of 20 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 heavily reinforced top and bottom
to span local anomalies such as by assuming an unsupported length of at
least 14 feet. Foundation walls acting as retaining structures should also
be designed to resist lateral earth pressures as discussed in the
Foundations 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 firm natural soils. The exposed
soils in footing area should then be moisture adjusted to near optimum and
compacted. If water seepage is encountered in the footing areas, we
should be contacted for further evaluation. Structural fill placed in footing
areas should be a granular material such as road base compacted to at least
95% of standard Proctor density at near optimum moisture content.
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 Ieast 55 pcf
for backfill consisting of the on-site soils. Cantilevered retaining structures which are
separate from the residence (if any) and can be expected to deflect sufficiently to mobilize
the full active earth pressure condition should be designed for a lateral earth pressure
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computed on the basis of an equivalent fluid unit weight of at least 45 pcf for backfill
consisting of the on-site soils.
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 95% 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% of the maximum standard Proctor
density. Care 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 backfill.
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 of the 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. Fill placed against the sides of the footings to resist lateral loads
should be compacted to at least 959 of the maximum standard Proctor density at a
moisture content near optimum.
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should be separated from all bearing walls and columns with expansion joints
6
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
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
interior slabs 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 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
should consist of granular soils devoid of vegetation, topsoil and oversized rock,
UNDERDRAIN SYSTEM
Although free water was encountered during our exploration at depths below probable
excavation, it has been our experience in the area that the water level can rise and local
perched groundwater can develop during times of heavy precipitation or seasonal runoff.
Frozen ground during spring runoff can also create a perched condition. We recommend
below -grade construction, such as retaining walls be protected from wetting and
hydrostatic pressure buildup by an underdrain system. Shallow crawlspace at a depth of
about 2 to 3 feet below existing ground surface should not need an underdrain provided
the perimeter wall backfill is well compacted and with positive surface slope away from
the foundation.
Where provided, 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 I (7o to a suitable gravity outlet. Free -draining
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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 1I feet deep and covered by filter
fabric such as Mirafi 140N.
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 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
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.
5) Landscaping which requires regular heavy irrigation should be located at
least 5 feet from foundation walls.
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
other biological contaminants (MOBC) developing in the future. If the client is
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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 boring 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
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
Reviewed by:
Steven L. Pawlak, P.E.
DAY/ksw
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1 1
151515
i
100 0 100 200
APPROXIMATE SCALE—FEET '\ `
00
O
O
I / w
1 ` O
2
V \ n
rrl
I' \.
I I 35 257 ac \ 0
16-7-308 H -P - KUMAR LOCATION OF EXPLORATORY BORING Fig. 1
a
0.40
J
9
a
0
0
5
15
20
BORING 1
ti
6/12
14.7IWC=
DD=107
4/12
WC=22.5
DD=99
50/6
4=35
200=15
74/12
LEGEND
C21
7
F
TOPSOIL; ORGANIC SANDY CLAYEY SILT, FIRM, MOIST, DARK BROWN.
CLAY AND SILT (CL—ML); SANDY TO VERY SANDY, MEDIUM STIFF,
MOIST TO VERY M015T, BROWN.
SAND (5M); SILTY, LOOSE, WET, BROWN.
GRAVEL (GM); SANDY, SILTY, COBBLES, DENSE, WET, BROWN.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION
TEST.
6/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 6 BLOWS OF
A 140—POUND HAMMER FALLING 30 INCHES WERE REQUIRED
TO DRIVE THE SAMPLER 12 INCHES.
WATER LEVEL ENCOUNTERED AT THE TIME OF DRILLING.
s DEPTH AT WHICH BORING CAVED FOLLOWING DRILIING.
NOTES
1. THE EXPLORATORY BORING WAS DRILLED ON AUGUST 10, 2016
WITH A 4—INCH DIAMETER CONTINUOUS FUGHT POWER AUGER.
2. THE EXPLORATORY BORING WAS APPROXIMATELY LOCATED IN
THE MIDDLE OF THE RESIDENCE SITE BY THE CLIENT.
3. THE ELEVATION OF THE EXPLORATORY BORING WAS NOT
MEASURED AND THE LOG OF THE EXPLORATORY BORING IS
PLOTTED TO DEPTH.
4. THE EXPLORATORY BORING LOCATION 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 THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER LEVEL SHOWN ON THE LOG WAS MEASURED
AT THE TIME AND UNDER CONDITIONS INDICATED. FLUCTUATIONS
IN THE WATER LEVEL MAY OCCUR WITH TIME.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (X) (ASTM D 2216);
DD = DRY DENSITY (pc() (ASTM D 2216);
4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
200 = PERCENTAGE PASSING NO. 200 SIEVE ASTM 0 1140).
16-7-308 H-P KUM R LOG OF EXPLORATORY BORING Fig. 2
1
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CONSOLIDATION - SWELLCONSOLIDATION - SWELL
1
0
1
2
3
4
5
0
1
2
3
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 0 2.5'
WC = 14.7 %, DD = 107 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
0
1 1.0 APPLIED PRESSURE — KSF 10 100
SAMPLE OF: Silly Sand
FROM: Boring 1 0 5'
WC = 22.5 % DD = 99 pcf
NO MOVEMENT UPON
WETTING
lh..s fart r.una appy only to Ito
W. tM0 4. 1M Winn .pint
0.d n.t be rnmed.e.d..mpl M
f.14 .1O.W 0. .Ott.. award et
KWnR and ....Giat.l. tn.. S..p
C..f.cd.Hpn bring pwfem.d i.
e..'I.Me .10 AVM G{'JM.
1.0 APPLIED PRESSURE — KSF 10 100
16-7-308 H-P I<UMAR SWELL -CONSOLIDATION TEST RESULTS Fig. 3
1
i
1
100
10
ea
70
60
50
40
30
20
HYDROMETER ANALYSIS SIEVE ANALYSIS
T)8( 4(401500 1.1.2 STANDARD 0(41(5 CLEe4 304+40 07(42.55
24 445 7 4193
45 92 15 111* 60424 11011 40IN 104 8793 4100 450 /70 130 /16 4I3 88 gi 3/6' ^ 1 f/x^ r 9^6^
g..001 .ocx 1 1 1 1 1 1
002 .001
1 1 1 1 1 1 1 1 1 .1 r
019 .037 .0 5 150 .3000 .400 1,10 2 30 4.75
DIAMETER OF PARTICLES IN MILLIMETERS
I r of I 1 r 1 1
1.5 16 36.1
0
10
20
30
AO
9
50
60 1(
70
e0
00
100
762 127 700153
CLAY TO SILT
SAND GRAVEL
FINE I MEDIUM !COARSE FINE I COARSE
COBBLES
GRAVEL 35 X SAND 50 2
SAMPLE 0F: Silty Sand and Grovel
SILT AND CLAY 15 74
FROM: Boring 1 0 10'
These lest result.' apply only la the
samples which were tested. The
lasting report shall not be reproduced.
e s5epl 'n 1411. without the written
o pprorol al Kumar & Asseci0tss.
Stere onoly111 testing is performed
0acordoncs with ASTM 0422, ASTM C136
and/ar ASTM 01140.
16-7-308 H -P KU MAR GRADATION TEST RESULTS Fig. 4
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ProjectNo. 16-
7-
308 SUMMARYOFLABORATORYTESTRESULTS SOILOR BEDROCKTYPE SandySiltyClay SiltySand11 SiltySandandGravelUNCONFINEDCOMPRESSIVESTRENGTHPSF) ATTERBERGLIMITS LIQUIDPLASTIC LIMITINDEXPERCENTPASSINGNO. 200 SIEVEGRADATION
a.. -
z.
CO
o
GRAVEL
VI
M
NATURAL DRY DENSITY Pcf)
N
a c
NATURAL MOISTURE CONTENT
IN
7
N
11SAMPLELOCATION DEPTH
R)
11BORING