Assessing the Slaking Behavior of Clay-Bearing Rocks - Marshall ...

Assessing the Slaking Behavior of
Clay-Bearing Rocks
Abdul Shakoor
Tej P. Gautam
Department of Geology, Kent State University
10 th Annual Technical Forum
GEOHAZARDS IMPACTING TRANSPORTATION IN
THE APPALACHIAN REGION
Columbus, OHIO

SHALES
CLAYSTONES
MUDSTONES
SILTSTONES
CLAY-BEARING ROCKS
Comprise approximately two-thirds of the stratigraphic column
Cover one-third of the total land area
Deteriorate rapidly upon exposure to atmospheric processes (low
durability)
Because of their low durability, clay-bearing rocks result in
numerous problems in engineering construction, especially slope
stability

A slope failure in
Pittsburgh caused by
low-durability
claystone

A slope failure in Ohio
caused by low-durability
claystone/mudstone

FIELD BEHAVIOR OF CLAY-BEARING ROCKS
Newly excavated rock mass
Because of extensive
disintegration, it is hard
to find an intact rock
block
One year after
excavation

RESEARCH OBJECTIVES
Assess the slaking
behavior of clay-bearing
rocks under natural
atmospheric conditions
and quantify the nature
of slaked material in
terms of grain size
distribution.

Twenty different clay-bearing rocks
were selected for the study including:
5 shales
5 claystones
5 mudstones
5 siltstones

SAMPLE LOCATION AND CLASSIFICATION
Potter et al. (1980)
classification was
used to classify
samples into
shales, claystones,
mudstones, and
siltstones
Laboratory Tests:
Slake durability index (I d2 , I d3 , I d4 , I d5 )
Grain size distribution of the slaked material
retained in 2 mm-mesh drum after the test

Slake Durability Test Apparatus

GSD of Slaked Material (Lab)
100
Shale (2)
100
Mudstone (3)
Percent retained by weight
80
60
40
20
0
100
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
10
Particle size (mm)
1
Percent retained by weight
80
60
40
20
0
100
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
10
Particle size (mm)
1
Shale
Mudstone
Percent retained by weight
100
80
60
40
20
0
100
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
Claystone (1)
10
Particle size (mm)
1
Samples after 5 th cycle
Percent retained by weight
100
80
60
40
20
0
100
Cycle 1
Cycle 2
Cycle 3
Cycle 4
Cycle 5
Siltstone (3)
10
Particle size (mm)
1
Claystone
Siltstone

Simulation of Field Slaking Behavior
• Twelve replicate samples of each of twenty claybearing
rocks were prepared. Each sample consisted
of 10 pieces, weighing 40-60 g, with a total weight
of 450 to 550 g. All sample pieces were retained on
1-inch sieve.
• Each replicate sample was placed in a 9-inch
diameter pan and exposed to natural climatic
conditions for 1 year period, from September 2009
to September 2010.
• After each month, one sample of each of four rock
types was removed and its grain size distribution
was determined.

Samples Being Exposed to Natural Climatic Conditions
• Picture: All samples on roof

Initial Samples
Shale
Mudstone
Claystone
Siltstone

After 1 Month
Shale
Mudstone
Claystone
Siltstone

After 3 Months
Shale
Mudstone
Claystone
Siltstone

After 6 Months
Shale
Mudstone
Claystone
Siltstone

After 9 Months
Shale
Mudstone
Claystone
Siltstone

Observations of Slaking Behavior
Sample Month-1 Month-3 Month-6 Month-9
Shale-3
Highly
fractured; very
few pieces
remained intact
Most pieces
crumbled into
smaller
particles
All pieces crumbled
into smaller
particles
All pieces crumbled
into small particles
(2-6.3 mm)
Claystone-
1
Highly
fractured;
hardly any
intact pieces left
Most pieces
crumbled into
smaller
particles
All pieces crumbled
into smaller
particles
All pieces crumbled
into approx. 2mmsize
particles
Mudstone-
3
Mostly intact
pieces; some
fractures
developed
Numerous
fractures
developed;
slightly-highly
fragmented
Most pieces
crumbled into
smaller particles
All pieces crumbled
into smaller, nearly
uniform particle size
(2-6.3 mm)
Siltstone-
3
All pieces
remained intact
All pieces
remained intact
All pieces remained
intact; a few small
fractures
developed
Some fractures
appeared but all
pieces remained
intact

GSD of Slaked Material (Field)
After 1, 3, 6, 9 Months
100
Shale (3)
100
Mudstone (3)
Percent retained by weight
80
60
40
20
0
100
Cycle 2
M1
M3
M6
M9
10
Particle size (mm)
1
Percent retained by weight
80
60
40
20
0
100
Cycle 2
M1
M3
M6
M9
10
Particle size (mm)
1
100
Claystone (1)
100
Siltstone (3)
Percent retained by weight
80
60
40
20
0
100
Cycle 2
M1
M3
M6
M9
10
Particle size (mm)
1
Percent retained by weight
80
60
40
20
0
100
Cycle 2
M1
M3
M6
M9
10
Particle size (mm)
1

Second cycle slake durability test
overestimates the durability for
claystones and underestimates
the durability for siltstones and
shales. For mudstones, it
appears to provide a more
representative value.

ASTM Description of Retained Material
Type I
Type II
Type III

100
Grain Size Distribution
Percent retained by weight
80
60
40
20
Shale (3)
Claystone (5)
Mudstone (3)
Siltstone (3)
0
100
10
Particle size (mm)
1
In order to represent a wide range of disintegration behavior of
clay-bearing rocks, a new parameter called “disintegration
ratio” was used (Erguler and Shakoor, 2009)

DISINTEGRATION RATIO
Disintegration Ratio ( D
R
)
A
A
C
T
AC = area under any grain size distribution curve
AT = total area encompassing grain size
distribution curves of all samples
Area ( bci )
D R
( Claystone 5)
0.003
Area ( abcd )
Area ( bcg )
D R
( Mudstone 3)
0. 315
Area ( abcd )
Area ( fbce )
D R
( Siltstone 3)
0. 926
Area ( abcd )
DR = 1, Completely durable
DR = 0, Completely non-durable

Disintegration Ratio vs. Slake Durability
Index (2 nd cycle) - Lab Results
1
Disintegration ratio
0.8
0.6
0.4
0.2
0
y = 0.0001x 2 - 0.004x
R 2 = 0.87
0 20 40 60 80 100
Slake durability index (I d2 )

Disintegration Ratio (Field Samples) vs. Slake
Durability Index (2 nd cycle)
Disintegration ratio (3 months)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
0 20 40 60 80 100
Slake durability index (I d2 )

CONCLUSIONS
• Slake durability test does not predict the field
behavior of clay-bearing rocks.
• During the 9-months period of exposure, claystone
and mudshale completely disintegrated during the
first 3 months, whereas siltstone was found to be
the most durable. Mudstone exhibited an average
disintegration behavior.
• A wide range of disintegration behavior, as indicated
by the particle size distribution of slaked material,
can be described using the disintegration ratio.

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