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

Chapter 6 SLOPE STABILITY
The factor of safety for the wedge can be and computed by:
FOS =
Horizontal Resisting Forces
Horizontal Driving forces
= P p + cL
P a
(6.2)
P a = Active force (driving)
P p = Passive force (resisting)
cL = Resisting force due to cohesive clay
For method of computation of the active force and passive forces reader can refer to the Chapter 7
on retaining wall.
6.7 SLOPE STABILIZATION METHODS
Slope stabilization methods generally aim to reduce driving forces, increase resisting forces, or
both. Driving forces can be reduced by excavation of materials from appropriate part of the
unsuitable ground and drainage of water to reduce the hydrostatic pressures acting on the unstable
zone. Resisting forces can be increased by introducing soil reinforcements, such as soil nails and
geo-synthetic materials, and retaining structures or other supports.
6.7.1 Slope Flattening
Slope flattening is a common method for increasing the stability of a slope by reducing the driving
forces that contribute to movements. Often, it is the first option to be considered when stabilizing a
slope.
Existing Slope Profile
Regrading Slope Profile
6.7.2 Drainage
Figure 6.9 Schematic View of Slope Regrading Work
Surface (berm, toe, interceptor, and cascade drains) and subsurface (horizontal drains and gravel
trenches) drainages are essential for treatment of any slide or potential slide. Proper drainage
system can reduce the destabilizing hydrostatic and seepage forces on a slope as well as the risk of
erosion.
March 2009 6-13