HomeMy WebLinkAboutSoils Report 03.10.2020IC+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 crkumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
Auorfare
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT IS -12, ASPEN GLEN, FILING 2
12 COLUMBINE
GARFIELD COUNTY, COLORADO
PROJECT NO. 20-7-157
MARCH 10, 2020
PREPARED FOR:
RM CONSTRUCTION
ATTN: BLAKE PILAND
5030 COUNTY ROAD 154
GLENWOOD SPRINGS, COLORADO 81601
b lake(W, buildwith rm.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
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 - LEGEND AND NOTES
FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS
FIGURE 5 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. ® Project No. 20-7-157
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot IS -12, Filing 2, Aspen Glen, 12 Columbine, 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 RM Construction dated February 24, 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.
PROPOSED CONSTRUCTION
Design plans were conceptual at the time of this study. In general, the proposed residence will
be a single -story structure. Ground floor could be slab -on -grade or structural above crawlspace.
Grading for the structure is assumed to be relatively minor with cut depths between about 2 to
5 feet. We assume relatively light foundation loadings, typical of the proposed type of
construction.
When building location, grading and loading information have been developed, we should be
notified to re-evaluate the recommendations presented in this report.
SITE CONDITIONS
The site was vacant with minor snow covering the ground at the time of our field exploration.
The ground was vegetated with grass and weeds. The site is located in the valley bottom with
the terrain gently sloping generally down to the north. The adjacent lots are developed with 1
and 2 -story, single family residences.
Kumar & Associates, Inc. ® Project No. 20-7-157
2
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen 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 sinkholes to develop and can produce areas of
localized subsidence. During previous work in the area, several sinkholes were observed
scattered throughout Aspen Glen, mainly east of the Roaring Fork River. These sinkholes appear
similar to others associated with the Eagle Valley Evaporite in areas of the middle to lower
Roaring Fork River valley.
Sinkholes were not observed on the subject lot. 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 L24 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 below the site is desired, we should be
contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on March 5, 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, Inc.
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
Kumar & Associates, Inc. ® Project No. 20-7-157
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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 consist of about one foot of topsoil overlying 5 to 51/2 feet of very stiff, sandy silty clay
underlain by dense, slightly silty sandy gravel and cobbles with boulders to the depths explored
of 8'/2 to 11 feet. Drilling in the coarse granular soils with auger equipment was difficult due to
the cobbles and 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 soil, presented on Figure 4, indicate low to
moderate compressibility under conditions of loading and wetting with a minor to low expansion
potential when wetted under light loading. Results of gradation analyses performed on a small
diameter drive samples (minus 11/2 -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 natural silty clay soils encountered in about the upper 6 feet of the borings possess low
bearing capacity and variable compressibility/expansion potential when loaded and wetted. The
underlying gravel soils possess moderate bearing capacity and typically low settlement potential.
At assumed excavation depth, the subgrade is expected to be clay soils but deeper excavation
could expose either materials. Spread footings placed on the natural soils should be feasible for
foundation support of the residence. The compressibility/expansion potential of the clay soils
should be further evaluated at the time of excavation. To reduce the risk of differential
movement due to the variable bearing conditions, the footings could be extended down to the
natural gravel soils.
Kumar & Associates, Inc. ® Project No. 20-7-157
4
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural soils.
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 2,000 psf. Footings placed entirely on the natural
dense granular soils can be designed for an allowable bearing pressure of 3,500
psf. Based on experience, we expect initial settlement of footings constructed on
the natural soils will be about 1 inch or less and could be differential between clay
and gravel bearing soils. Additional movement of about %2 inch could occur with
footings bearing on the clay soils if they become wetted.
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 firm natural soils. The exposed soils in
footing area should then be moistened and compacted.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
Kumar & Associates, Inc. ® Project No. 20-7-157
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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. 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 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 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 0.30 for clay soils and 0.50 for gravel soils. Passive pressure
of compacted backfill against the sides of the footings can be calculated using an equivalent fluid
unit weight of 450 pcf for gravel backfill. 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
Kumar & Associates, Inc. ® Project No. 20-7-157
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of passive resistance. Fill placed against the sides of the footings to resist lateral loads should be
a granular material 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, appear suitable to support lightly loaded slab -on -
grade construction. The expansion potential of the clay soils should be further evaluated at the
time of excavation and the need for sub -excavation to a depth of around 2 feet and replacement
with compacted structural fill. 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 any) 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 and where there are clay soils 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,
crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by
an underdrain system.
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
Kumar & Associates, Inc. ® Project No. 20-7-157
-7-
a suitable gravity outlet or drywell based in the underlying granular soils. 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 11/2 feet deep.
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 6 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in paved areas. Free -draining wall backfill should be
covered with filter fabric and capped with about 2 feet of the on-site finer graded
soils to reduce surface water infiltration.
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 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
Kumar & Associates, Inc. ® Project No. 20-7-157
8
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 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, lc
Steven L. Pawl
Reviewed by:
Daniel E. Hardin, P.E.
SLP/kac
Kumar & Associates, Inc. ®
Project No. 20-7-157
3
8820043
3931 102014
R820048
9319 02019
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BORING 1
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APPROXIMATE SCALE -FEET
20-7-157
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS
Fig. 1
1
E
1
gE
1-
w
w
O
a
w
0
— 0
5
-- 10
BORING 1
EL. 100'
11
34/12
WC=6.8
DD=108
16/12
WC=9.6
DD=100
-200=81
BORING 2
EL. 100'
//I 24/12
/ 16/12
WC=9.8
/ DD=104
51/12
WC=1 .3
+4=58
-200=7
50/3
0
5
10 —
15 15
a
w
0
20-7-157
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
kw
i
TOPSOIL; SANDY SILT AND CLAY WITH ORGANICS, BROWN.
CLAY (CL); SILTY, SANDY, VERY STIFF, SLIGHTLY MOIST, RED, LOW PLASTICITY,
SLIGHTLY POROUS, CALCAREOUS TRACES.
GRAVEL AND COBBLES (GM—GP); SLIGHTLY SILTY, SANDY, PROBABLE BOULDERS,
DENSE, SLIGHTLY MOIST, ROUNDED ROCK.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
IDRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
34/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 34 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
t PRACTICAL AUGER REFUSAL.
NOTES
i. THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 5, 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 MEASURED BY HAND LEVEL AND REFER
TO BORING 1 AS 100', ASSUMED.
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).
20-7-157
Kumar & Associates
LEGEND AND NOTES
Fig. 3
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
1
0
1
2
—3
4
5
2
1
0
1
2
1 0 APPLIED PRESSURE - KSF
10
T00
20-7-157
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
SAMPLE OF: Sandy Silty Clay
FROM: Boring 2 IP 5'
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 CO 2.5'
WC = 9.8 %, DD = 104 pcf
WC = 6.8 %, DD = 108 pcf
I
1
Li L
�''�
— EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
N
These teenne apply only to The
samples tested. The testing sport
shall not be reproduced, exc pt In
full, without the written approval of
(Kumar and Associates, Inc. Swell
iConsolidation testing perform d in
accordance with ASTM D-4546,
1 0 APPLIED PRESSURE - KSF
10
T00
20-7-157
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
SAMPLE OF: Sandy Silty Clay
FROM: Boring 2 IP 5'
WC = 9.8 %, DD = 104 pcf
I
1
Li L
�''�
— EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
These teenne apply only to The
samples tested. The testing sport
shall not be reproduced, exc pt In
full, without the written approval of
(Kumar and Associates, Inc. Swell
iConsolidation testing perform d in
accordance with ASTM D-4546,
1 0 APPLIED PRESSURE - KSF
10
T00
20-7-157
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
100
90
80
70
60
5
50
40
30
20
10
0
42$ 2.0
DIAMETER OF PARTICLES IN MILLIMETERS
152
CLAY TO SILT
SAND
GRAVEL
FINE
MEDIUM
COARSE
FINE
COARSE
COBBLES
GRAVEL 58
LIQUID LIMIT
SAMPLE OF: Slightly Silty Sandy Gravel
SAND
35
PLASTICITY INDEX
SILT AND CLAY 7
FROM: Boring 2 ® 7.5'
10
20
30
40 B
a
50
60 a
70
80
90
100
These test results apply only to The
samples which were tested. The
ilte report shall not be reproduced,
cotes In full, without the written
approval of Kumar & Associates, Inc.
Slave analysis testing Is performed In
accordotle6 with ASTM D6913, ASTM D7929,
ASTM C136 and/or ASTM D1140.
20-7-157
Kumar & Associates
GRADATION TEST RESULTS
Fig. 5
HYDROMETER ANALYSIS
SIEVE ANALYSIS
24 HRS 7 HRS
45 MIN 5 MIN
6p.8N
TIME READINGS
191WN 4M1N 2N)N
12y10
/100
U
6
5. STANDARD SERIES
0 j40 435 ;I
.42)
4D
44
3/8"
CLEAR
3/4"
SQUARE
I
OPENINGS
2" 5'
6'
- j
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.006. .1108
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.075
.150
.300 1 .600
1.18. 1 2,36
4.75
9
5 16
38,1
763
927
201
42$ 2.0
DIAMETER OF PARTICLES IN MILLIMETERS
152
CLAY TO SILT
SAND
GRAVEL
FINE
MEDIUM
COARSE
FINE
COARSE
COBBLES
GRAVEL 58
LIQUID LIMIT
SAMPLE OF: Slightly Silty Sandy Gravel
SAND
35
PLASTICITY INDEX
SILT AND CLAY 7
FROM: Boring 2 ® 7.5'
10
20
30
40 B
a
50
60 a
70
80
90
100
These test results apply only to The
samples which were tested. The
ilte report shall not be reproduced,
cotes In full, without the written
approval of Kumar & Associates, Inc.
Slave analysis testing Is performed In
accordotle6 with ASTM D6913, ASTM D7929,
ASTM C136 and/or ASTM D1140.
20-7-157
Kumar & Associates
GRADATION TEST RESULTS
Fig. 5
1(+A
Kumar & Associates, Inc.®
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 20-7-157
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSRY(%)
(pct)
GRADATION
PERCENT
PASSING
200 SIEVE
ATTERBERG LIMITS
1 UNCONFINED
COMPRESSIVE
STRENGTH
[Ps`1
SOIL TYPE
BORING
DEPTH
(ft)
--
GRAVEL
SAND
(%)
LIQUID LIMIT
(%)
PLASTIC
INDEX
(%)
1
21/z
6.8
108
Sandy Silty Clay
5
9.6
100
81
Sandy Silty Clay
2
5
9.8
104
Sandy Silty Clay
7Y2
1.3
58
35
7
Slightly Silty Sandy Gravel