HomeMy WebLinkAboutSubsoil Study for Foundation Design 02.27.15~tech
HEPWORTH·PAWLAK GEOTECHNICAL
SUBSOIL STUDY
Hepworth-Pawlak Geotechnical, Inc.
5020 County Road 154
Glenwood Springs, Colorado 81601
Phone: 970-945-7988
Fax: 970-945-8454
Email: hpgeo@hpgeotech.com
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 78, RIVER BEND WAY
GARFIELD COUNTY, COLORADO
JOB NO. 115 055A
FEBRUARY 27, 2015
PREPARED FOR:
JONATHAN PETTIT
574 RIVER BEND WAY
GLENWOOD SPRINGS, COLORADO 81601
jon@churchill-groop.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY ............................................................................ -1 -
PROPOSED CONSTRUCTION ..................................................................................... -1-
SITE CONDITIONS ....................................................................................................... - 2 -
GEOLOGY ...................................................................................................................... -2-
FIELD EXPLORATION ................................................................................................. -3 -
SUBSURFACE CONDITIONS ...................................................................................... -3 -
FOUNDATION BEARING CONDITIONS ................................................................... -4 -
DESIGN RECOMMENDATIONS ................................................................................. -5 -
DEEP FOUNDATION ................................................................................................ -5 -
FOUNDATION ALTERNATIVE .............................................................................. -5 -
FOUNDATION AND RETAINING WALLS ............................................................ -7 -
FLOOR SLABS (NON-STRUCTURAL) ................................................................... -8 -
UNDERDRAIN SYSTEM .......................................................................................... -8 -
SURFACE DRAINAGE ............................................................................................. -9 -
LIMITATIONS ............................................................................................................. -10 -
FIGURE 1 -LOCATION OF EXPLORATORY BORINGS
FIGURE 2 -LOGS OF EXPLORATORY BORINGS
FIGURE 3 -LEGEND AND NOTES
FIGURES 4 and 5 -SWELL-CONSOLIDATION TEST RESULTS
TABLE 1 -SUMMARY OF LABORATORY TEST RESULTS
Job No. 115 055A
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located
on Lot 78, River Bend Way, 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 proposal for geotechnical
engineering services to Jonathan Pettit dated February 11, 2015.
A field exploration program consisting of exploratory borings and pits was conducted on
the lot 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 potential 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 general proposed construction and the subsurface conditions
encountered.
PROPOSED CONSTRUCTION
Development on the lot had not been determined at the time of our study and we
understand the findings of our study will be considered in the purchase of the lot. In
general, we assume the proposed residence will be a 2-story, wood frame structure with
an attached garage. A basement could be included in the building plan. Ground floors
could be structural above crawlspace or basement level in the living area. Garage and
basement floors would probably be slab-on-grade. Grading for the structure is assumed
to be relatively minor with cut depths between about 3 to 12 feet. We assume relatively
light foundation loadings, typical of the proposed type of construction.
When building loadings, location and grading plans have been developed, we should be
notified to re-evaluate the recommendations contained in this report.
Job No. 115 055A
-2-
SITE CONDITIONS
The lot is located on a strongly sloping alluvial fan along the uphill, western side of River
Bend Way. The Robertson Ditch (now buried) and easement borders the uphill side of
the lot roughly 10 feet higher than the building area. A broad surface swale which drains
to the north separates the higher ground to the west from the main area of the lot. The
ground surface of the lot has been graded relatively flat with apparent shallow fill placed
in the central to eastern part during the subdivision development and is gently sloping
down to the east across the proposed building area. Vegetation consists mainly of weeds
with scattered small brush on the lot. The underground utilities to the lot are complete
and the lot is essentially unchanged since its original grading in 2006-2007. Lot 79
located to the south is developed with a residence surrounded with irrigated sod, and Lot
77 located to the north is vacant and roughly 5 feet lower in elevation. A couple inches of
fresh snow covered the lot at the time of our filed exploration.
GEOLOGY
The geologic conditions were described in our previous report conducted for planning and
preliminary design of the overall subdivision development dated October 29, 1997, Job
No. 197 327. The surficial soils below the fill on the lot mainly consist of sandy silt
alluvial fan deposits with inter-bedded sandy and gravelly layers overlying gravel terrace
alluvium of the Roaring Fork River. The river alluvium is mainly a clast-supported
deposit of rounded gravel, cobbles and boulders up to about 3 feet in size in a silty sand
matrix which extends down to depths on the order of 35 to 40 feet below ground surface
and overlies siltstone/claystone bedrock in the area of Lot 78.
The underlying bedrock consists of the Eagle Valley Evaporite which contains gypsum
and is generally associated with scattered sinkhole development in the Roaring Fork
River valley. An apparent sinkhole was observed along the south side of River Bend
Way and River Bank Lane intersection about 200 feet southeast of Lot 78. The sinkhole
was excavated and backfilled during construction of the roadway. A sinkhole occurred in
Job No. 115 055A
- 3 -
the parking lot adjoining to the golf cart storage tent in 2005 located about 1,400 feet to
the northwest of Lot 78 which was backfilled and compaction grouted. Both sinkholes
have not shown signs of reactivation such as ground subsidence since their remediation.
Subsurface voids have not been encountered in borings drilled into the bedrock near Lot
78 and the potential for subsidence due to dissolution of the evaporite throughout the
service life of the residence, in our opinion, is low, but the owners of the lot should be
aware of the sinkhole potential and the risk of future subsidence.
FIELD EXPLORATION
The field exploration for the project was conducted on February 24, 2015. Three
exploratory pits were dug and two exploratory borings were drilled at the locations shown
on Figure 1 to evaluate the subsurface conditions. Because of previous cobbles and
difficult drilling encountered in the upper fill soils, backhoe pits were dug to loosen the
fill material followed by the exploratory boring drilling. The borings were advanced with
4-inch diameter continuous flight augers powered by a truck-mounted CME-45B drill rig.
The borings and pits were logged by a representative of Hepworth-Pawlak Geotechnical,
Inc.
Samples of the subsoils were taken with 1 % 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 Logs of Exploratory Borings,
Figure 2. The samples were returned to our laboratory for review by the project engineer
and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsoil profiles encountered in the borings are shown on Figure 2.
The subsoils consist of about 5 to 6 feet of silty clayey sandy gravel and cobble fill
overlying about 14 feet of loose/medium stiff to stiff sandy silt and clay (debris fan
Job No. 115 055A
-4-
deposits) above 3Yz to 5 feet of medium dense, silty sand with gravel overlying dense,
slightly silty sandy gravel, cobbles and probable boulders (river alluvium) at depths of
22Yz to 25Yz feet down to the drilled depths of 26 and 28 feet. Pits 1, 2 and 3 respectively
encountered about 5, 6 and 5Yz feet of fill above the silt and clay soils. Drilling with
auger equipment in the dense river alluvium was difficult due to the cobbles and boulders
and close to practical drilling refusal in the deposit.
Laboratory testing performed on samples obtained from the borings included natural
moisture content and density and finer than sand size gradation analyses. Results of
swell-consolidation testing performed on relatively undisturbed drive samples of the
sandy silt and clay soil, presented on Figures 4 and 5, generally indicate low to moderate
compressibility under loading and a low collapse potential (settlement under constant
load) when wetted. The samples showed moderate compressibility under additional
loading after wetting.
No free water was encountered in the borings at the time of drilling. The soils in Boring
1 were moist to highly moist with depth and the soils in Boring 2 were slightly moist to
moist with depth. The irrigated lawn of Lot 79 to the south has a moderate grade down to
Lot 78 which could be a source of moisture to Lot 78. The Robertson Ditch could also be
a source of moisture although it has been piped since the subdivision development in
roughly 2005 -2006.
FOUNDATION BEARING CONDITIONS
The subsoils encountered in the borings are variable in moisture content and consistency.
The upper silt and clay (debris fan) soils typically have low bearing capacity and low to
moderate settlement potential when wetted under loading and extend down roughly7 18 1.
feet below a shallow foundation such as footings or structural (mat) slab. Considering the
compressible nature of the debris fan soils and the potential for (or continued) wetting
from site development irrigation, spread footings placed on the natural silt and clay soils
could have a high risk of excessive settlement and are not recommended for the building
foundation support. Foundations that extend down to the dense, river gravel alluvium
Job No. 115 055A
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(such as piers or piles) would have moderate bearing capacity and low settlement risk and
are recommended for the building support.
DESIGN RECOMMENDATIONS
DEEP FOUNDATION
Considering the compressibility potential of the debris fan soils encountered at the site
and the nature of the proposed construction, we recommend piles or piers that extend
down into the underlying river gravel alluvium be used for building support. Deep
foundations can typically consist of drilled or pushed micro-piles or helical piers. We
expect the piles or piers will be at least 20 feet long and penetrate the river gravel to
achieve downward allowable pile load capacity on the order of20 to 40 kips. Uplift
capacity will depend on the helix size(s) or pile diameter and embedment material and
length. Settlements under sustained loading are expected to be minor, less than Yz inch.
Lateral load capacity is normally provided by battered piles. Piles should be spaced at
least 3 feet from center to center to avoid reduction from group action. Chemical testing
was not performed on the on-site soils. Although it has been our experience that the pile
capacity and steel section will greatly exceed the design value and the required design life
of the piling system will not be compromised, the piling contractor should verify that the
pilings have adequate corrosion potential for this site. Grade beams and pile caps should
have a minimum depth of 3 feet for frost cover and void form below them is not needed.
We can assist with additional soil and site parameters as needed.
FOUNDATION ALTERNATIVE
As an alternative with a risk of differential settlement and distress, the buildings could be
founded with a heavily reinforced structural slab or post-tensioned slab foundation
bearing on at least 5 feet of compacted structural fill. If a basement is provided, the
structural fill would also need to go below the lower building level.
The design and construction criteria presented below should be observed for a slab
foundation system.
Job No. 115 055A
- 6 -
1) A structural slab or post-tensioned slab placed on at least 5 feet of
compacted structural fill should be designed for an allowable bearing
pressure of 1,000 psf. Post-tensioned slabs placed on structural fill should
be designed for a wetted distance of 10 feet but at least half of the slab
width whichever is more. Initial settlement of the foundation is estimated
to be about 1 inch or less. Additional differential settlement of about 1 to
2 inches is estimated if deep wetting of the debris fan soils were to occur.
2) The thickened sections of the slab for support of concentrated loads should
have a minimum width of 20 inches.
3) The perimeter tum-down section of the slab should be provided with
adequate soil cover above the bearing elevation for frost protection.
Placement of foundations at least 36 inches below exterior grade is
typically used in this area. If a frost protected foundation is used, the
perimeter tum-down section should have at least 18 inches of soil cover.
4) The foundation should be constructed in a "box-like" configuration rather
than with irregular extensions which can settle differentially to the main
building area. The foundation walls, where provided, 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 (if any) should also be designed to resist lateral earth pressures
as discussed in the "Foundation and Retaining Walls" section of this
report.
5) The root zone and any loose or disturbed soils should be removed.
Structural fill placed below the slab bearing level or the existing fill should
have compaction to at least 98% of the maximum standard Proctor density
within 2 percentage points of optimum moisture content and can consist of
the onsite soils.
6) A representative of the geotechnical engineer should evaluate the
compaction of the fill materials during its placement and observe all
footing excavations prior to concrete placement for bearing conditions.
Job No. 115 055A
- 7 -
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 are
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 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 as described in the Underdrain System section.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisture content near optimum. Backfill placed 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 the foundation or retaining wall footings will be a combination of
the sliding resistance of the foundation on the bearing materials and passive earth
pressure against the side of the foundation. Resistance to sliding at the bottoms of
shallow foundations can be calculated based on a coefficient of friction of 0.35. Passive
pressure of compacted backfill against the sides of the foundation can be calculated using
Job No. 115 055A
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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
foundation to resist lateral loads should be compacted to at least 95% of the maximum
standard Proctor density at a moisture content near optimum.
FLOOR SLABS (NON-STRUCTURAL)
The natural on-site soils and compacted fill are suitable to support lightly loaded slab-on-
grade construction. The upper silt soils have variable settlement potential when wetted
under load and there could be some post-construction slab movement ifthe subgrade soils
become wet. 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 4 inch layer of free-draining gravel should be placed beneath
basement level slabs (if provided) 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 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 that 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 and
basement areas (if provided), be protected from wetting and hydrostatic pressure buildup
Job No. 115 055A
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by an underdrain system. An underdrain should not be provided around shallow
foundations (such as garage and shallow crawlspace areas).
Where installed around basement areas (if constructed), 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 1 % to a
suitable gravity outlet, sump and pump or drywell based in the underlying river gravel
deposit. 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 of 2 inches. The drain gravel backfill should be at least 1 Yz feet deep. In
silt soil bearing areas, an impervious membrane, such as a 30 mil PVC liner, should be
placed in a trough shape below the drain gravel and attached to the foundation wall with
mastic to prevent wetting of the bearing soils.
SURF ACE DRAINAGE
Providing proper perimeter surface grading and drainage will be critical in the satisfactory
performance of the building. The following drainage precautions should be observed
during construction and maintained at all times after the building 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 10% for at least 5 feet and preferably 10
feet away from the building in unpaved areas and a minimum slope of2Yz
inches in the first 10 feet in paved areas. Free-draining basement wall
backfill (if constructed) should be covered with filter fabric and capped
Job No. 115 055A
-10 -
with at least 2 feet of the on-site, fine grained soils to reduce surface water
infiltration.
4) Roof gutters should be provided with downspouts that discharge at least 5
feet beyond the foundation and preferably into subsurface solid drain pipe
to suitable discharge. Surface swales should have a minimum grade of
4%.
5) Landscaping which requires regular heavy irrigation, such as sod, should
be located at least 10 feet from foundation walls. Consideration should be
given to use of xeriscape to help prevent subsurface wetting 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
Job No. 115 055A
-11 -
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.
Steven L. Pawlak, P.E.
Reviewed by:
Daniel E. Hardin, P .E.
SLP/ksw
Job No. 115 055A
APPROXIMATE SCALE
1" = 30'
S9f3o
ROBERTSON DITCH ......_
BELOW PEDESTRIAN PATH ......_ -......
115 055A
/
LOT79
(EXISTING
RESIDENCE)
~------------~~~~~'""""'~-
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------------------5955 ------/
--5950 --- -----,
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LOT78
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BORING 1 • • PIT 1
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RIVER BEND WAY
LOT77
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~ LOCATION OF EXPLORATORY BORINGS
HEPWORTH•PAWLAK GEOTECHNICAL
Figure 1
5955
5950
5945
1D
~
c:: 5940
0
'§
6)
iii
5935
5930
5925
115 055A
BORING 1
ELEV.= 5951.5'
9/12
5/12
WC=22.2
00=97
6/12
5/12
WC=27.1
00=97
-200=93
10/12
WC=15.4
-200=47
35/12
BORING2
ELEV.= 5953'
16/12
12/12
WC=13.6
00=109
9/12
WC=10.9
00=105
17/12
WC=16.3
00=106
-200=91
6/6,20/6
WC=B.1
00=100
-200=26
65/6
Note: Explanation of symbols is shown on Figure 3.
~ LOGS OF EXPLORATORY BORINGS
HEPWORTH•PAWLAK GEOTECHNICAL
5955
5950
5945
1D ~
5940 c::
0
'§
6)
iii
5935
5930
5925
Figure 2
LEGEND:
FILL; silty clayey sandy gravel with cobbles and small boulders, medium dense, moist, brown, organics and very
moist at ground surface, low plastic fines.
SILT AND CLAY (ML-CL); slightly sandy to sandy, medium stiff and very moist at Boring 1, stiff and moist at
Boring 2, light brown to brown, low plasticity.
SAND (SM); silty, scattered gravel, stratified silt and clay lenses , medium dense, moist, mixed brown , medium to
coarse sand.
GRAVEL AND COBBLES (GM-GP); silty, sandy, probable boulders, dense, moist, brown, rounded rock.
5/12
NOTES:
Relatively undisturbed drive sample; 2-inch l.D. California liner sample.
Drive sample; standard penetration test (SPT), 1 3/8 inch l.D. split spoon sample, ASTM D-1586.
Drive sample blow count; indicates that 5 blows of a 140 pound hammer falling 30 inches were
required to drive the California or SPT sampler 12 inches .
1. Exploratory borings were drilled on February 24, 2015 with 4-inch diameter continuous flight power auger.
2. Locations of exploratory borings were measured approximately by pacing from features shown on the site plan
provided.
3. Elevations of exploratory borings were obtained by interpolation between contours shown on the site plan provided
and their relative elevation checked by hand level.
4. The exploratory boring locations and elevations 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
115 055A ~
HEPWORTH•PAWLAK GEOTECHN.lCAL
LEGEND AND NOTES Figure 3
Moisture Content = 22.2 percent
Dry Density = 97 pct
Sample of: Sandy Silt and Clay
From: Boring 1 at 8 Feet
0 -r--........... _ -...... ---~ /
-~ ..... 1 ~ ('"
'~ ---No movement
'*' upon
c: 2 wetting 0
'ij)
\ rn Q) ..... c.
E 3 0 \ (.)
4
0 .1 1.0 10 100
APPLIED PRESSURE -ksf
Moisture Content= 13.6 percent
Dry Density = 109 pct
Sample of: Sandy Silt and Clay
From: Boring 2 at 10 Feet
0
'*' r\J
c:: (' -~ 0 1 ~
'ij) --rn ........... r--r-. Compression ~ ~ r-.--.....
c. ~ upon
E wetting 0 2 (.) r't )
3
0.1 1.0 10 100
APPLIED PRESSURE -ksf
115 055A ~ SWELL-CONSOLIDATION TEST RESULTS Figure 4
HEPWORTH-PAWLAK GEOTl!CHNICAL
Moisture Content = 10.9 percent
Dry Density = 105 pct
Sample of: Sandy Silt and Clay
From: Boring 2 at 15 Feet
0
r" ~
1>..::.__ < :.-i..--
'#. 1
c:: ~"' r--. ,_,_ .... ._Compression
0
'(jj ~~ upon
r/) wetting ~ 2 a. "t) E
0
0
3
0.1 1.0 10 100
APPLIED PRESSURE -ksf
115 055A ~
HEPWORTli•PAWLAK GEOTECHNICAL
SWELL-CONSOLIDATION TEST RESULTS Figure 5
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1 Job No. 115 OSSA
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION NATURAL GRADATION AmRBERG LIMITS UNCONFINED
MOISTURE NATURAL GRAVEL SAND PERCENT COMPRESSIVE DRY DENSITY PLASTIC SOIL OR BORING DEPTH CONTENT PASSING NO. LIQUID LIMIT STRENGTH (%) (%) 200SIEVE INDEX BEDROCK TYPE
(ft) (%) (pc:f) (%1 1%) (PSF )
1 8 22.2 97 Sandy Silt and Cl~y
15 27 .1 97 93 Slightly Sandy Silt and Clay
20 15.4 47 Very Silty Sand
2 10 13.6 109 Sandy Silt and Clay
15 10.9 105 Sandy Silt and Clay
20 16.3 106 91 Slightly Sandy Silt and Clay
25 8.1 100 26 Silty Sand