Recent
SLOPE STABILITY PROBABILITY
CLASSIFICATION (SSPC)
Robert Hack
Engineering Geology, ESA,
International Institute for Geoinformation Sciences and Earth Observation (ITC), University
Twente, The Netherlands
Kota Kinabalu, Malaysia, 8 April 2011
University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
1
Slope stability
University
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
2
Causes and triggers for in-stability of a
slope
University
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
3
What causes in-stability of a slope ?
•
•
•
Wrong design
(e.g. too steep, too high)
Decrease in the future of ground mass
properties
(e.g. weathering, vegetation)
Changes in future geometry
(e.g. scouring, erosion, human influence – road
cut)
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
4
What triggers in-stability of a slope ?
•
•
Earthquakes (extra stress)
Rainfall (changes the properties)
These are not causes (!) because:
• Should have been anticipated in design, or
• For long standing slopes (e.g. natural slopes): There has
been an earthquake or rainfall before and then it did not
collapse
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
5
What is required to analyse the stability
of a slope ?
•
•
•
•
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ground mass properties
present and future geometry
present and future geotechnical behaviour
of ground mass
external influences such as earthquakes,
rainfall, etcetera
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
6
ground mass properties
In virtually all slopes is a considerable variation
Therefore:
First divide the soil or rock mass in:
homogene “geotechnical units”
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Homogene geotechnical unit?
Is that possible ?
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Variation
Heterogeneity of mass causes:
• variation in mass properties
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Geotechnical unit:
A “geotechnical unit” is a unit in which
the geotechnical properties are the
same.
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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geotechnical units are based on the experience
and expertise of the interpreter
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“No geotechnical unit is really homogene….”
A certain amount of variation has to be
allowed as otherwise the number of
units will be unlimited
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12
“The allowable variation of the properties
within one geotechnical unit depends on:
the degree of variability of the properties
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within a mass,
the influence of the differences on
engineering behaviour, and
the context in which the geotechnical unit
is used.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
13
Smaller allowed variability of the properties in
a geotechnical unit results in:
higher accuracy of geotechnical calculations
less risk that a calculation or design is wrong
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
14
Smaller allowed variability of the properties in
a geotechnical unit:
requires collecting more data and is thus more
costly
geotechnical calculations are more
complicated and complex, and cost more time
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
15
Hence:
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the variations allowed within a geotechnical unit for
a slope along a major highway is smaller
the variations allowed within a geotechnical unit for
a slope along a farmers road will be larger
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Examples
What are the implications if the units are
wrongly assumed in a design?
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Original situation
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design error
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Example 2: Many discontinuity sets
with large variation in orientation
(too many for the design engineer?)
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Example 3: Many discontinuity
sets with large variation in
orientation
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bedding planes
Example 4: Variation in
clay content in intact rock
causes differential
weathering
April 1990
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Slightly higher clay content
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Example 4: Variation
in clay content in
intact rock causes
differential
weathering
April 1992
mass slid
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Example 4: Variation in clay content in intact
rock causes differential weathering
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Characterizing and future stability of slopes - Robert Hack – Kota Kinabalu,
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Uncertainty
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Uncertainty in properties
Uncertainty (error) in measurements of properties
Uncertainties in geometry
Uncertainty (error) in measurements of geometry
(often small)
Uncertainty in failure mechanisms applicable
Uncertainty in future environment (for example,
weathering)
Magnitude of external influences such as
earthquakes, rainfall, etc. not certain
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Options for analysing slope
stability
Analytical
Numerical
Classification
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Analysing slope stability
analytical: only in relatively simple cases
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possible for a discontinuous rock mass
numerical: difficult and often cumbersome,
(however, possible with discontinuous
numerical rock mechanics programs such as
UDEC & 3DEC)
Characterizing and future stability of slopes - Robert Hack – Kota Kinabalu,
27
Analysing slope stability(2)
Extra work for deterministic numerical methods is
justified if:
Quantity and quality of input data is high
E.g.:
- representative tests of discontinuity (i.e. joint)
shear strength of each discontinuity family
- orientations of each discontinuity
- etcetera, etcetera.
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Characterizing and future stability of slopes - Robert Hack – Kota Kinabalu,
28
Analysing slope stability(3)
High quality and quantity of data not only of the
rock mass at the slope face but also in the slope!
Hence:
excavate the side and rebuilt (then it is exactly
known)
or
many large-sized borehole samples required
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Characterizing and future stability of slopes - Robert Hack – Kota Kinabalu,
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Analysing slope stability(4)
High quality and quantity of data of rock mass
inside the slope rock mass are virtually never
available because far too expensive to obtain
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Characterizing and future stability of slopes - Robert Hack – Kota Kinabalu,
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Analysing slope stability(5)
Solution often used:
Use a numerical program and estimate the
input parameters
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Characterizing and future stability of slopes - Robert Hack – Kota Kinabalu,
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Analysing slope stability(6)
How can properties be estimated:
rock mass classification
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Characterizing and future stability of slopes - Robert Hack – Kota Kinabalu,
32
Slope classification systems
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Classification systems are
empirical relations that relate rock
mass properties either directly or
via a rating system to an
engineering application, e.g.
slope, tunnel
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2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Classification systems:
For underground (tunnel):
• Bieniawski (RMR)
• Barton (Q)
• Laubscher (MRMR)
• etcetera
For slopes:
• Selby
• Bieniawski (RMR)
• Vecchia
• Robertson (RMR)
• Romana (SMR)
• Haines
• SSPC
• etcetera
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Development of many rock mass
classification systems
First developed for underground excavations
Most slope systems are based on
underground systems adjusted to be used for
slopes
Therefore a legacy in parameters from
underground (read “tunnel”) systems
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Development of many rock mass
classification systems
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Most systems that are used at present are based
on systems developed some 30 years ago
At that time “state-of-the-art” and new, but this is
no reason not to investigate whether the systems
are still as applicable or that new methodologies
(for example, with the use of computers) allow for
better systems
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
37
Many rock mass classification
systems
Wide variation in rating systems,
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methodologies, parameters, calculation
methods, boundaries, etc.
Wide variation in the influence of
parameters on the final result
In some un-understandable ratings and
relations
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Strange influence parameters in
some systems
For example:
A slope in a rock mass with a high
intact rock strength and one thick
clay filled (gauge type)
discontinuity set that will lead to
sliding failure.
UCS = 150 MPa
35º
clay-filled
discontinuity
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Strange influence parameters in
some systems
In some systems the intact rock strength will
partially determine the stability rating, while the
slope will be unstable due to the presence of the
thick clay filled discontinuity and not at all be
UCS = 150 MPa
influenced by the intact rock strength.
How valid is such a system?
35º
clay-filled
discontinuity
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No clear differentiation between
“as is” and “as will be”
External influences as weathering and
method of excavation will have
influenced the site characterized but
will also (and likely differently)
influence the new slope in the future
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Slope Stability probability
Classification (SSPC)
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SSPC
• three step classification system
• based on probabilities
• independent failure mechanism assessment
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Three step classification system (1)
proposed new road cut
old road
river
1
slightly
weathered
2
fresh
3
Reference
Rock Mass
moderately
weathered
1: natural exposure made by scouring of river, moderately weathered;
2: old road, made by excavator, slightly weathered; 3: new to develop
University
road
cut, made by modern blasting,
moderately
weathered
to fresh.
2011-04-08
- Kota Kinabalu - Recent
SSPC - Robert Hack
Twente.
44
Three step classification system (2)
EXPOSURE ROCK MASS (ERM)
Exposure rock mass parameters significant for slope stability:
• Material properties: strength, susceptibility to weathering
• Discontinuities: orientation and sets (spacing) or single
• Discontinuity properties: roughness, infill, karst
Exposure specific parameters:
• Method of excavation
• Degree of weathering
Factor used to remove the influence of the
method excavation and degree of weathering
REFERENCE ROCK MASS (RRM)
Reference rock mass parameters significant for slope stability:
• Material properties: strength, susceptibility to weathering
• Discontinuities: orientation and sets (spacing) or single
• Discontinuity properties: roughness, infill, karst
Slope specific parameters:
• Method of excavation to be used
• Expected degree of weathering at
end of engineering life-time of slope
SLOPE GEOMETRY
Orientation
Height
Factor used to assess the influence of the
method excavation and future weathering
SLOPE ROCK MASS (SRM)
Slope rock mass parameters significant for slope stability:
• Material properties: strength, susceptibility to weathering
• Discontinuities: orientation and sets (spacing) or single
• Discontinuity properties: roughness, infill, karst
SLOPE STABILITY ASSESSMENT
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Excavation specific parameters for
the excavation which is used to
characterize the rock mass
• Degree of weathering
• Method of excavation
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Rock mass Parameters
• Intact rock strength
• Spacing and persistence discontinuities
• Shear strength along discontinuity:
- Roughness
•
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- large scale
- small scale
- tactile roughness
- Infill
- Karst
Susceptibility to weathering
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
47
Slope specific parameters for the
new slope to be made
• Expected degree of weathering at
•
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end of lifetime of the slope
Method of excavation to be used for
the new slope
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Intact rock strength
By simple means test:
hammer blows, crushing by hand,
etcetera
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Spacing and persistence of
discontinuities
Determine block size and block form by:
• visual assessment, followed by:
• quantification (measurement) of the
characteristic spacing and orientation of each
set
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amplitude roughness:
≈ 5 – 9 cm
wavy
i = 14 - 20°
≈ 5 – 9 cm
slightly wavy
i = 9 - 14°
≈ 3.5 – 7 cm
i = 4 - 8°
Shear
strength
curved
slightly curved
≈ 1.5 – 3.5 cm
i = 2 - 4°
roughness
large scale
straight
≈1m
(i-angles and dimensions only approximate)
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stepped
undulating
amplitude roughness > 2 - 3 mm
amplitude roughness > 2 - 3 mm
Shear
strength
roughness
small scale
planar
≈ 0.20 m
(dimensions only approximate)
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Three classes:
rough
smooth
polished
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Shear
strength
roughness
tactile
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Infill:
-
cemented
-
no infill
-
non-softening (3 grain sizes)
-
softening (3 grain sizes)
-
gauge type (larger or smaller
than roughness amplitude)
-
flowing material
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Shear
strength
Infill
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Shear strength
karst
Options: karst or no karst
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Shear strength - condition factor
Discontinuity condition factor (TC) is a
multiplication of the ratings for:
- small-scale roughness
- large-scale roughness
- infill
- karst
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Orientation dependent stability
Stability depending on relation between
slope and discontinuity orientation
For example:
• Plane and wedge sliding
• Toppling
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Orientation dependent stability
Discontinuity related shear strength failure
Plane sliding(1)
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Orientation dependent stability
Discontinuity related shear strength failure
Plane sliding(2)
Conditions:
- discontinuity must daylight
- downward stress > shear strength
along discontinuity plane
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Orientation dependent stability
Discontinuity related shear strength failure
Wedge sliding
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Orientation dependent stability
Discontinuity related shear strength failure
Wedge sliding
Conditions:
- intersection line must daylight
- downward stress > shear strength along
discontinuity planes
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Orientation dependent stability
TC (= discontinuity condition parameter) (-)
How was it developed
1
0.8
0.6
0.4
TC = 0.0113 * AP (AP in deg)
0.2
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stable
unstable
0
0
20
40
60
AP (= apparent discontinuity dip in direction slope dip) (deg)
80
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Orientation dependent stability
Sliding criterion
sliding occurs if :
TC < 0.0113 * AP
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Orientation dependent stability
Sliding probability
95 %
70 %
50 %
30 %
5%
TC (condition of discontinuity)
1.00
discontinuity stable
with respect to sliding
0.80
0.60
discontinuity unstable
with respect to sliding
0.40
0.20
0.00
0
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10
20
30
40
50
60
70
80
90
AP (deg)
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Orientation dependent stability
Discontinuity related shear strength failure
Toppling
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Orientation dependent stability
Toppling criterion
TC < 0.0087 * (− 90° − AP + dipdiscontinuity )
TC = discontinuity condition factor
AP = apparent discontinuity dip in direction
of slope dip
DIPdiscontinuity = dip of discontinuity
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Orientation dependent stability
Toppling probability
TC (condition of discontinuity) (-)
1.00
95 %
Fig. 9. Toppling criterion.
70 %
50 %
30 %
discontinuity stable
with respect to toppling
0.80
5%
0.60
0.40
discontinuity unstable
with respect to toppling
0.20
0.00
0
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10
20
30
40
50
60
70
80
90
- 90 - AP + slope dip (deg)
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Orientation independent stability
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Orientation independent stability
Slope instability not dependent on the orientation
of discontinuities in relation with the slope
orientation
E.g. in situations:
• No discontinuities
• Too high stress for the soil or rock intact
material strength (e.g. slope too high)
• So many discontinuities in so many directions
that there is always a failure plane (comparable
to a soil mass)
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Orientation independent stability
In SSPC based on:
• Intact rock strength
• Block size and form
• Condition of discontinuities
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Orientation independent stability
1
Overall spacing
of discontinuity
sets
0.8
2 discontinuity sets
minimum spacing
maximum spacing
0.7
factor
Block size
and form
relations from
Taylor
1 discontinuity set
0.9
3 discontinuity sets
minimum spacing
intermediate spacing
maximum spacing
0.6
0.5
factor1
0.4
factor3
factor2
0.3
0.2
bedding1
&
joint3
0.1
0.1
1
joint2
10
100
1000
discontinuity spacing (cm)
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Orientation independent stability
Overall condition of discontinuity
sets
TC1 TC2 TC3
+
+
DS1 DS 2 DS3
CD =
1
1
1
+
+
DS1 DS 2 DS3
TC1, 2,3 are the condition, and DS1, 2,3 are
the spacings of discontinuity sets 1, 2, 3
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Orientation independent stability
Shear plane failure following MohrCoulomb for rock mass
If the dip slope ≤ ϕ ’ mass :
the maximum slope height ( H max ) is infinite
else
-4
=
.
*
1
6
10 * coh’ mass *
H max
sin dip slope * cos (ϕ’ mass )
(
(
)
1 - cos dip slope - ϕ ’ mass
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)
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Probability orientation independent failure
10
Das hed pr obabilit y lines indi c at e that the number of sl opes us ed f or
the devel opment of the SSPC s ys tem f or t hes e s ec tions of the
graph is limited and the pr obability lines may not be as c ert ai n as
the pr obability lines dr awn wit h a conti nuous line.
95 %
H max / Hslope
probability to be stable > 95 %
90 %
70 %
50 %
30 %
1
10 %
5%
(example)
probability to be stable < 5 %
0.1
0.0
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0.2
0.4
0.6
ϕ’mass / slope dip
0.8
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1.0
74
Comparison between SSPC and
other classification systems
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75
80
a: SSPC
60
b: Haines
60
number of slopes (%)
number of slopes (%)
80
visually estimated stability
stable (class 1)
unstable (class 2)
unstable (class 3)
40
20
Haines safety factor: 1.2
40
20
0
0
<5
7.5
15
25
35
45
55
65
75
85
92.5
> 95
-45
SSPC stability probability (%)
stable
80
60
-25
-10
-5
5
15
25
35
45
unstable
stable
Percentages are from total number of slopes
per visually estimated stability class.
visually estimated stability
stable (class 1)
unstable (class 2)
unstable (class 3)
c: SMR
-35
Haines' slope dip - existing slope dip (deg)
unstable
number of slopes (%)
visually estimated stability
stable (class 1)
unstable (class 2)
unstable (class 3)
visually estimated stability:
class 1 : stable; no signs of present or future slope
failures (number of slopes: 109)
class 2 : small problems; the slope presently shows
signs of active small failures and has the potential for
future small failures (number of slopes: 20)
class 3 : large problems; The slope presently shows
signs of active large failures and has the potential for
future large failures (number of slopes: 55)
40
20
0
5
15
completely
unstable
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25
35
45
55
65
75
Romana's SMR (points)
'tentative' describtion of SMR classes:
partially
unstable
stable
stable
85
95
completely
stable
Comparison
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Examples
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Poorly blasted slope
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Poorly blasted slope
New cut (in 1990):
Visual assessed: extremely poor; instable.
(SSPC stability < 8% for slope height 13.8 m high, dip 70°, rock mass
weathering: 'moderately' and 'dislodged blocks' due to blasting).
Forecast in 1996: SSPC final stability: slope dip 45°.
In 2002: Slope dip about 55° (visually assessed unstable).
In 2005: Slope dip about 52°
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Slope Stability probability
Classification (SSPC)
Saba case - Dutch Antilles
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Landslide in harbour
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Geotechnical zoning
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SSPC results
Pyroclastic deposits
Rock mass friction
Rock mass cohesion
Calculated maximum
possible height on the
slope
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Calculated SSPC
35°
39kPa
13m
Laboratory / field
27° (measured)
40kPa (measured)
15m (observed)
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Failing slope in Manila, Philippines
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Failing slope in Manila (2)
• tuff layers with near horizontal weathering horizons
(about every 2-3 m)
• slope height is about 5 m
• SSPC non-orientation dependent stability about 50%
for 7 m slope height
• unfavourable stress configuration due to corner
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Widening
existing road in
Bhutan
(Himalayas)
University
Twente.
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Bhutan
Method of
excavation
University
Twente.
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Widening
existing road in
Bhutan
(Himalayas)
University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Widening existing road in
Bhutan (Himalayas)
Above road level:
• Various units
• Joint systems (sub-) vertical
• Present slope about 21 m high, about 90° or
overhanging (!)
• Present situation above road highly unstable (visual
assessment)
Below road level:
• Inaccessible – seems stable
University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Widening existing road in
Bhutan (Himalayas)
Above road level:
• Following SSPC system about 12 – 27 m for a 75°
slope (depending on unit) (orientation independent
stability 85%)
Below road level:
• Inaccessible – different unit ? – and not disturbed by
excavation method
University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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SSPC extensions:
measuring discontinuities
&
future decay of slope material
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Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Heterogeneity
• even if uncertainty is included this is only up to
•
a certain extend – what extend is to the
discretion of the engineer
can heterogeneity be defined by an automatic
procedure , e.g. for example Lidar
University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Heterogeneity (2)
(modified after Slob et al, 2002)
University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Future degradation of soil or rock
due to weathering, ravelling, etc.
no reliable quantitative relations exist to forecast
the future geotechnical properties of soil or rock
mass
University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Future degradation (2)
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Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Future degradation (3)
3.5
z [m]
3.0
2.5
2.0
1.5
1.0
7.0
7.5
Excavated 1999
8.0
8.5
y [m]
May 2001
9.0
9.5
May 2002
Reduction in slope angle due to weathering, erosion and ravelling (after Huisman)
University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Degradation processes
•
•
•
University
Twente.
Main processes involved in degradation:
Loss of structure due to stress release
Weathering (In-situ change by inside or outside
influences)
Erosion (Material transport with no chemical or
structural changes)
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Significance in engineering
• When rock masses degrade in time, slopes
and other works that are stable at present
may become unstable
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Twente.
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University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Erosion
• Essentially: migration of solid or dissolved material
• Weathering occurs usually before and possibly
•
University
Twente.
during erosion
Transporting agents:
- Water
- Gravity
- Ice
- Wind
- Man!
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Quantify weathering: SSPC
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Twente.
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Weathering in time
• The susceptibility to weathering is a concept that is
•
frequently addressed by “the” weathering rate of a
rock material or mass.
Weathering rates may be expected to decrease with
time, as the state of the rock mass becomes more and
more in equilibrium with its surroundings.
University
Twente.
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Weathering rates
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Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Weathering rates
WE ( t ) =
WEinit − R
app
WE
log (1 + t )
WE(t) = degree of weathering at time t
WEinit = (initial) degree of weathering at time t = 0
RappWE = weathering intensity rate
WE as function of time, initial
weathering and the
weathering intensity rate
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Twente.
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Weathering rates
•Material:
Gypsum layers
Gypsum cemented siltstone layers
Middle Muschelkalk near Vandellos (Spain)
University
Twente.
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Weathering rates
-
Balance between weathering and erosion
(or generally) decay, and
exposure orientation dependent features,
such as: sunlight, wind, and rain.
Middle Muschelkalk near Vandellos (Spain)
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Twente.
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Weathering intensity rate
siltstone
(with gypsum cement)
Weathering intensity rates R(appWE) for Middle Muschelkalk, siltstone
(gypsum cemented), versus slope dip-direction (after Huisman)
University
Twente.
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Weathering intensity rate
gypsum
Weathering intensity rates R(appWE) for Middle Muschelkalk, gypsum,
versus slope dip-direction (after Huisman)
University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Weathering intensity rate
SSPC system with applying weathering
intensity rate:
- original slope cut about 50º (1998)
- in 15 years decrease to 35º
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Twente.
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Conclusions
SSPC system in combination with degradation
forecasts gives:
• reasonable design for slope stability
• with minimum of work and
• in a short time
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Twente.
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Kota Kinabalu, Malaysia
University
Twente.
2011-04-08 - Kota Kinabalu - Recent SSPC - Robert Hack
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Kota Kinabalu, Malaysia
Side road: 5 years old
slightly weathered
SSPC
stability:
Sandstone:
stable
Shale:
unstable
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Twente.
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Kota Kinabalu, Malaysia
Main road: 10 years old
moderately weathered
SSPC
stability:
Sandstone:
stable
Shale:
ravelling
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Twente.
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Kota Kinabalu, Malaysia
SSPC friction & cohesion:
friction (deg)
cohesion (kPa)
shale
slightly (5 years)
moderately (10 years)
4
2
2.4
1.1
sandstone
slightly (5 years)
moderately (10 years)
20
11
10.0
6.3
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Twente.
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Kota Kinabalu, Malaysia
Expected stability when sandstone highly weathered:
Main road: (30 deg slope dip; 6 m high)
10% (i.e. instable)
Side road: (45 deg slope dip; 8 m high)
< 5 % (i.e. instable)
University
Twente.
WHEN ??????
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Literature
Hack HRGK (2002) An evaluation of slope stability classification. Keynote Lecture & article. Proc. ISRM
EUROCK’2002, Portugal, Madeira, Funchal, 25-28 November 2002. Editors: C. Dinis da Gama & L. Ribeira e
Sousa, Publ. Sociedade Portuguesa de Geotecnia, Av. do Brasil, 101, 1700-066 Lisboa, Portugal. pp. 3 – 32.
Hack HRGK, Price, D & Rengers N (2003) A new approach to rock slope stability - a probability classification
(SSPC). Bulletin of Engineering Geology and the Environment. Springer Verlag. Vol. 62: article: DOI
10.1007/s10064-002-0155-4. pp. 167-184 & erratum: DOI 10.1007/s10064-002-0171-4. pp 185-185.
Hack HRGK, Price D & Rengers N (2005) Una nueva aproximación a la clasificación probabilística de estabilidad
de taludes (SSPC). In "Ingeniería del Terreno", IngeoTer 5. chapter 6. publ. U.D. Proyectos, E.T.S.I. Minas Universidad Politécnica de Madrid. ISBN 84-96140-14-8. pp. 418.
Huisman M, Hack HRGK & Nieuwenhuis JD (2006) Predicting rock mass decay in engineering lifetimes: the
influence of slope aspect and climate. Environmental & Engineering Geoscience. Vol XII, no. 1, Feb. 2006, pp.
49-61.
Price, DG (2009) Engineering geology : principles and practice. De Freitas (ed), MH. Berlin, Springer, 2009. 450 p.
ISBN: 978-3-540-29249-4.
Slob S, Hack HRGK, Knapen B van & Kenemy J (2004) Digital outcrop mapping and determination of rock mass
properties using 3D terrestrial laser scanning techniques In: Schubert, W. (ed.): Rock Engineering – Theory
and Practice. Proceedings of the ISRM Regional Symposium Eurock 2004 & 53rd Geomechanics Colloquy.
Verlag Glückauf, Essen, Germany, ISBN 3-7739-5995-8, pp. 449-452.
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