Volume 6 – Geotechnical Manual, Site Investigation and Engineering ...

Chapter 6 SLOPE STABILITY
6 SLOPE STABILITY
6.1
INTRODUCTION
Slope stability addresses the tendency of soil masses to attain an
equilibrium
state between the
strength of the soil and the force of gravity. In JPS, slope stability problems most often occur in the
construction of embankment over soft soils, and the instability of waterway slope (e.g. river and
pond) due to seepage, drawdown, or erosion by flowing water. Placement of stockpiles, heavy
equipment, or other surcharges may also cause instabilities of
the slope, particularly
during
construction stage. In general,
altered slope, whether man-made or natural need to be analyzed
and checked to ensure that it has adequate factor of safety against slope failure.
The factor of safety
against slope failure is defined as the ratio of the resisting forces to the
driving
forces tending to cause movement for a given failure configuration.
The analysiss of slope stability is
therefore the analytical procedure of determining the most critical, i.e. the lowest factor of safety of
a given
or proposed
slope configuration.
6.2
TYPE OF SLOPE INSTABILITIES
In general, slope stability problems commonly encountered in JPS can be categories into three
types, namely:
6.2.1
Infinite Slope Failure
A slope
that extends for a relatively long distance and has a consistent subsurface profile may be
analyzed as an infinite slope, see Figure 6.1. The failure
plane for this case is parallel to the surface
of the slope and the
limit equilibrium method can be applied readily.
Figure 6.1 Infinite Slope Failure
6.2.2
Sliding Block Failure
Sliding block failure
occurs when the wedgee type of sliding mass that cut through the fill and a thin
layer of
weak soil essentially moves as a block. This concept is as shown in Figure 6.2.
March 2009
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