2. SUBMITTED BY SHAH ZEB ALI
SUBMITTED TO SIR YASIR SARFRAZ SB
ROLL NO 261
CLASS EVENING B
SEMESTER 6TH
INSTITUTE OF GEOLOGY
THE UNIVERSITY OF AZAD JAMMU AND KASHMIR
MUZAFFARABAD
4. • SLOPE FAILURES ARE ESSENTIALLY NATURAL
HAZARDS THAT OCCUR IN MANY AREAS
OVER THE WORLD.
• POPULARLY KNOWN AS LANDSLIDES,
SLOPE FAILURES DESCRIBE A WIDE VARIETY
OF MECHANISMS THAT CAUSE THE
OUTWARD OR DOWNWARD MOVEMENT OF
SLOPE-FORMING MATERIALS LIKE ROCK,
SOIL OR LANDFILLS.
• LANDSLIDE CAN RESULT EITHER FROM
ROCK FAILURE OR SOIL FAILURE.
Failure Modes Introduction
5. • Material is constantly moving downslope in response to
gravity.
Movement can be very slow, barely perceptible over many
years. Or, movement can be devastatingly rapid, apparent
within minutes. Whether or not slope movement occurs
depends on slope steepness and slope stability.
Slopes lose strength over time through numerous events and
certain lithologies lend itself more to specific types of failure.
6. Rock Slope Failure
In rock slope failure, the failure plane is
predetermined.
The orientation and spacing of the discontinuities
plane with respect to the slope face are the
determinants of rock slope failure.
Failure could arise from a single discontinuity, a
pair of intersecting discontinuities or a pattern of
multiple discontinuities that form a failure mode.
7. TYPES OF SLOPE FAILURES
There are main four types of failures which are:
1. Plane failure
2. Wedge failure
3. Toppling failure
4. Rotational failure
8. Plane Failure
A rock slope undergoes this mode of failure when
combinations of discontinuities in the rock mass form
blocks or wedges within the rock which are free to
move.
The pattern of the discontinuities may be comprised
of a single discontinuity or a pair of discontinuities
that intersect each other, or a combination of
multiple discontinuities that are linked together to
form a failure mode.
A planar failure of rock slope occurs when a mass of
rock in a slope slides down along a relatively planar
failure surface. The failure surfaces are usually
structural discontinuities such as bedding planes,
faults, joints or the interface between bedrock and
an overlying layer of weathered rock.
10. The favorable conditions of plane failure are as
follows:
The dip direction of the planar discontinuity must
be within ( ±20o
) of the dip direction of the slope
face.
The dip of the planar discontinuity must be less
than the dip of the slope face .
The dip of the planar discontinuity must be greater
than the angle of friction of the surface.
11. Wedge Failure
Wedge failure can occur in rock mass with two or
more sets of discontinuities whose lines of
intersection are approximately perpendicular to
the strike of the slope and dip towards the plane
of the slope.
This mode of failure requires that the dip angle of
at least one joint intersect is greater than the
friction angle of the joint surfaces and that the line
of joint intersection intersects the plane of the
slope.
13. The necessary structural conditions for this failure are
summarized as follows:
The trend of the line of intersection must
approximate the dip direction of the slope face.
The plunge of the line of intersection must be less
than the dip of the slope face. The line of
intersection under this condition is said to daylight on
the slope.
The plunge of the line of intersection must be
greater than the angle of friction of the surface.
14. Toppling Failure
Toppling failures occur when columns of rock,
formed by steeply dipping discontinuities in the
rock rotates about an essentially fixed point at or
near the base of the slope followed by slippage
between the layers.
The center of gravity of the column or slab must
fall outside the dimension of its base in toppling
failure.
Jointed rock mass closely spaced and steeply
dipping discontinuity sets that dip away from the
slope surface are necessary prerequisites for
toppling failure.
15. The removal of overburden and the confining
rock, as is the case in mining excavations, can
result in a partial relief of the constraining stresses
within the rock structure, resulting in a toppling
failure.
This type of slope failure may be further
categorized depend on the mode such as :
1. flexural toppling
2. block toppling and
3. block flexural toppling
17. Rotational Failure
In rotational slips the shape of the failure surface
in section may be a circular arc or a non-circular
curve.
In general, circular slips are associated with
homogeneous soil conditions and non-circular
slips with non-homogeneous conditions.
Translational and compound slips occur where
the form of the failure surface is influenced by the
presence of an adjacent stratum of significantly
different strength.
18. Translational slips tend to occur where the
adjacent stratum is at a relatively shallow depth
below the surface of the slope: the failure surface
tends to be plane and roughly parallel to the
slope.
Compound slips usually occurs where the
adjacent stratum is at greater depth, the failure
surface consisting of curved and plane sections.
The sliding of material along a curved surface
called a rotational slide.
20. Stabilization and Protection Methods
Stabilization of slopes is very important
and hence the expenditure on these
programs is justified as unstable slopes
can be hazardous.
Factor of safety is raised for slopes
near highways, railway tracks and
other important structures through
various stabilization methods.
Selection of suitable method
depends not only the technical
feasibility but on the cost and ease of
installation.
21.
22. There are some methods that reduce the driving force
behind slope failure, like pore water pressure.
Drainage is provided to reduce this pressure and reduce
the likelihood of slope failure. Providing drainage is less
expense than support stabilization techniques when it
comes to covering large slopes.
Excavation or removal of the upper portion of the slope is
another way to provide stability. Stability of all slope types
depends on height of the slope.
There are other methods that use support systems and
reinforcements to provide stability. Lastly, there
are protection techniques, usually employed where there is
high risk of rock falls or landslides and where stabilization is
insufficient or not feasible.
