HomeMy WebLinkAboutSoils Report 03.19.2020I(+A
Kumar & Associates, Inc.®
Geotechnical and Materials Engineers
and Environmental Scientists
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 95, IRONBRIDGE
304 RIVER BEND WAY
GARFIELD COUNTY, COLORADO
PROJECT NO. 20-7-165
MARCH 19, 2020
PREPARED FOR:
JAMES GORNICK BUILDING SPECIALISTS
ATTN: JIM GORNICK
1001 GRAND AVENUE
GLENWOOD SPRINGS, COLORADO 81601
(jgornick 1988 (cr gmail.com)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
BACKGROUND INFORMATION - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 3 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS - 4 -
FOUNDATION AND RETAINING WALLS - 5 -
FLOOR SLABS - 6 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - SWELL -CONSOLIDATION TEST RESULTS
FIGURE 4 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. ® Project No. 20-7-165
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 95, Ironbridge, 304 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 agreement for geotechnical engineering
services to James Gornick Building Specialists, dated February 27, 2020.
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.
BACKGROUND INFORMATION
Hepworth-Pawlak Geotechnical (now Kumar & Associates) previously performed a preliminary
geotechnical study in the subdivision which included the subject lot, report dated December 31,
2002, Job No. 101 196-1. Information from this report has been reviewed and considered in the
preparation of this report.
PROPOSED CONSTRUCTION
The proposed residence will be a single -story structure over crawlspace with a slab -on -grade
garage plus second level bonus room located between the boring locations shown on Figure 1.
Cut depths are assumed to be between 2 to 4 feet below the existing ground surface. Foundation
loadings for the proposed construction are assumed to be light.
If building location, grading or loading information changes, we should be notified to re-evaluate
the recommendations presented in this report.
Kumar & Associates, Inc. ® Project No. 20-7-165
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SITE CONDITIONS
T a-nra-n ar riostlp-tii turd Cli-fit f i
exploration although there was scattered gravel indicating possible past grading. The terrain is
gently sloping down to the east at a grade of about 5% in the building area then steepens slightly
to the east. Elevation difference across the building area is about 4 feet. Vegetation consists of
grass and weeds.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge Subdivision.
These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some
massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits
associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the
gypsum under certain conditions can cause areas of localized subsidence. During previous work
in the area, several sinkholes were observed scattered throughout the Ironbridge Subdivision.
These sinkholes appear similar to others associated with the Eagle Valley Evaporite in other
areas of the Roaring Fork River valley.
Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities
was encountered in the subsurface materials; however, the exploratory boring was 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 95, throughout the service life of the proposed structure, in our
opinion, is low and similar to other platted lots in the area; however, the owner should be made
aware of the potential for sinkhole development. If further investigation of possible cavities in
the bedrock below the site is desired, we should be contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on March 2, 2020. 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 augers powered by a truck-
mounted CME -45B drill rig. The borings were logged by a representative of Kumar &
Associates.
Kumar & Associates, Inc. ® Project No. 20-7-165
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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 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 subsurface conditions encountered at the site are shown on Figure 2. The
subsoils, below about one foot of topsoil, consist of about 4 to 5 feet of stiff, sandy silty clay and
sandy silt overlying dense, slightly silty, sandy gravel and cobbles with probable boulders.
Drilling in the coarse granular subsoils with auger equipment was difficult due to the cobbles and
probable boulders and drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and gradation analyses. Results of swell -consolidation testing performed on
relatively undisturbed drive samples of the clay soils, presented on Figure 4, indicate low to
moderate compressibility under loading with a minor expansion potential when wetted. Results
of gradation analyses performed on a small diameter drive sample (minus 1% inch fraction) of
the coarse granular subsoils are shown on Figure 5. 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.
FOUNDATION BEARING CONDITIONS
The upper fine-grained clay soils possess low bearing capacity and low movement potential.
The underlying coarse granular, sandy gravel and cobble soils possess moderate bearing capacity
and relatively low settlement potential.
At assumed excavation depths, the subgrade could transition the clay and coarse granular soils.
Spread footings placed on the natural soils appear suitable with a risk of settlement mainly if the
Kumar & Associates, Inc. ® Project No. 20-7-165
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clay soils are wetted. Placing the footings entirely on the coarse granular soils or compacted
structural fill could be used to limit post -construction settlement potential.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the building can be founded with spread footings bearing on the
natural soils or compacted structural fill.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils or 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 of about 1/2 to 1 inch if the clay soils were wetted after construction.
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
areas should then be moistened and compacted. Structural fill placed to
reestablish design bearing level should consist of a relatively well graded granular
Kumar & Associates, Inc. ° Project No. 20-7-165
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soil compacted to at least 98% 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 least 50 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. Backfill should not contain organics,
debris or rock larger than about 6 inches.
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% of the maximum
standard Proctor density at a moisture content at or slightly above 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 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
Kumar & Associates, Inc. ® Project No. 20-7-165
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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 350 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 95% of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade
construction with a low movement risk. 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 relatively well graded sand and gravel such as road base should be placed beneath slabs
for support. 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 vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
It is our understanding the proposed finished floor elevation at the lowest level is at or above the
surrounding grade and the crawlspace will be relatively shallow, around 3 feet deep. Therefore,
a foundation drain system is not required. 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 create a perched condition. We recommend below -grade
construction, such as retaining walls and basement areas, be protected from wetting and
hydrostatic pressure buildup by an underdrain and wall drain system.
Kumar & Associates, Inc. ® Project No. 20-7-165
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If the finished floor elevation of the proposed structure is revised to have a floor level below the
surrounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
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 10
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 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
Kumar & Associates, Inc. ® Project No. 20-7-165
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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,
Kumar & Associates
Steven L. Pawlak
Reviewed by:
Daniel E. Hardin, P.E.
SLP/kac
Kumar & Associates, Inc. ` Project No. 20-7465
4$
25 0 25 5[}
APPROXIMATE SCALE -FEET
LOT 94
20-7-165
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS
Fig. 1
DEPTH-FEET
0
5
10
BORING 1
EL. 5959'
BORING 2
EL. 5954.5'
0
19/12
f WC=7.8
DD=113
15/12
WC=7.1
DD=107
3/6,40/6 r 30/12
WC=10.3 WC=2.0
DD=93 +4=54
-200=57 -200=10
20/6,50/5
50/4
5-
10-
15
0-
15 15
20 20
1-
w
w
w
1
O
a
w
20-7-165
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
TOPSOIL; ORGANIC SANDY SILT AND CLAY, WITH GRAVEL AT BORING 1, FIRM, MOIST, DARK
BROWN.
/ / CLAY (CL); SILT` , SANDY, VERY STIFF, SLIGH-1`LY Iry 61ST, BROWN, LOW PLASTI Y.
19/12
t
SILT AND SAND (ML—SM); SLIGHTLY CLAYEY, SCATTERED GRAVEL, STIFF/MEDIUM DENSE,
SLIGHTLY MOIST, BROWN.
GRAVEL AND COBBLES (GM—GP); SLIGHTLY SILTY, SANDY, PROBABLE BOULDERS, DENSE,
SLIGHTLY MOIST, BROWN, ROUNDED ROCK.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
DRIVE SAMPLE BLOW COUNT. INDICATES THAT 19 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 2, 2020 WITH A 4—INCH—DIAMETER
CONTINUOUS—FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
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 THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (pcf) (ASTM D2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140).
20-7-165
Kumar & Associates
LEGEND AND NOTES
Fig. 3
2
CONSOLIDATION
CONSOLIDATION - SWELL
0
1
2
3
1
0
1
2
3
—4
10 APPLIED PRESSURE - KSF
10
100
SAMPLE OF: Sandy Clay with Gravel
FROM: Boring 1 ® 2.5'
WC = 7.8 %, DD = 113 pcf
r—
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
These test remade apply only to the
•wmples [seed. The testing reyart
,hall not be reproduced, esc pt in
lull, without the written approval of
Kumar and Associates, Inc. Swell
Coneolldatlon testing performed In
!accordance with AMU D-4548.
10 APPLIED PRESSURE - KSF
10
100
10 APPLIED PRESSURE -- KSF
10
100
20-7-165
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
SAMPLE OF: Sandy Clay
FROM: Boring 2 0 2.5'
WC = 7.1 %, DD = 107 pcf
r—
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
These test remade apply only to the
•wmples [seed. The testing reyart
,hall not be reproduced, esc pt in
lull, without the written approval of
Kumar and Associates, Inc. Swell
Coneolldatlon testing performed In
!accordance with AMU D-4548.
10 APPLIED PRESSURE -- KSF
10
100
20-7-165
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
1
HYDROMETER ANALYSIS
SIEVE ANALYSIS
24 HRS 7 HRS
-yULg
S-19AN4
TIME READINGS
H IMU�i1+1
U.S.
STANDARD
SERIES
.
CLEAR 00119110 OPCHINOS
- ,� - w
jll5.
100
memiElm
0
un
ses
-
OG
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r
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WF
=
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20
70
7-a1
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30
I
BO
40
aa�e
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1
50
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1
50
4o
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e0
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1
1
30
1
1
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70
Iwo
f
20
1
ao
I—
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10
`
1
00
1
A
0 I—
.001 .002 .005
1-1— r1— 1 rl�rn 1—
.009 .010 .037 .078 .150 .300
DIAMETER OF PARTICLES
11—t
I ACO
.425
0.
IN MILLIMETERS
a 12.39 4.75
2.0
1 I
1.8
5a
30.1
1 1
76.2
1 1 1 1
127
192
200
100
CLAY TO
SAND
GRAVEL
SILT
FINE MEDIUMCOBBLES
MEDIUM COARSE
FINE
GRAVEL 54 % SAND 36 X SILT AND CLAY 10 X
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Slightly Silty Sandy Gravel FROM: Boring 2 0 5'
These test results apply only to the
samples which ware tested. The
teslfng report shall not be reproduced,
excapl In full, without the wrlllen
approval of Kumar & Associates. Inc.
Sieve analysis testing Is performed In
accordance with ASTM D6913, ASTM D792B,
ASTM C13$ and/or ASTM D1140.
20-7-165
Kumar & Associates
GRADATION TEST RESULTS
Fig. 5
I{urnar & Assnci:ates Inn G
'(+Aand Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 20-7-165
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY(%)
(pct}
GRADATION
PERCENT
PASSING NO.
200 SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
ipsf)
SOI TYPE
BORING
DEPTH
(ft)
GRAVEL
SAND
(%)
LIQUID LIMIT
(9/°)
PLASTIC
INDEX
(%)
1
21/2
7.8
113
Sandy Clay lith Gravel
5
10.3
93
57
Very Sandy ilt with
Gravel
2
2'/2
7.1
107
Sandy Clay
5
2.0
54
36
10
Slightly Silty Sandy Gravel
C