TM 5-818-1 / AFM 88-3, Chap. 7
(1) Slopes in cohesionless materials
this method may be much smaller than values calculated
where the critical failure mechanism is shallow sliding or
by more accurate methods. An example is presented in
figures 8-9 through 8-11. Various trial circles must be
assumed to find the critical one. If φ large and c is small,
(2) Slopes where a relatively thin layer of
soil overlies firmer soil or rock and the critical failure
it may be desirable to replace the circular sliding surface
mechanism is sliding along a plane parallel to the slope,
by plane wedges at the active and passive extremities of
at the top of the firm layer.
the sliding mass.
e. Shear strength increasing with depth and φ
c. The simplified wedge method. This method
= 0. A chart for slopes in soils with shear strength
is a simple and conservative procedure for analyzing
increasing with depth and + = 0 is shown in figure 8-7.
noncircular surfaces. An example is shown in 8-12.
Various trial failure surfaces with different locations for
active and passive wedges must be assumed. The base
Detailed analyses of slope stability.
of the central sliding wedge is generally at the bottom of
If the simple methods given for estimating slope stability
a soft layer.
do not apply and site conditions and shear strengths
have been determined, more detailed stability analyses
may be appropriate. Such methods are described in
Stabilization of slopes. If a slide is being
engineering literature, and simplified versions are
stabilized by flattening the slope or by using a buttress or
retaining structure, the shear strength at time of failure
a. The method of moments for φ = 0. This
corresponding to a factor of safety of 1 should be
calculated. This strength can be used to evaluate the
method is simple but useful for the analysis of circular
slip surfaces in φ = 0 soils, as shown in figure 8-8.
safety factor of the slope after stabilization. Methods for
stabilizing slopes and landslides are summarized in table
b. The ordinary method of slices. This simple
8-1. Often one or more of these schemes may be used
and conservative procedure for circular slip surfaces can
together. Schemes I through V are listed approximately
be used in soils with φ > 0. For flat slopes with high pore
in order of increasing cost.
pressures and φ > 0, the factors of safety calculated by