(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

surface raveling.

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

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

engineering literature, and simplified versions are

stabilized by flattening the slope or by using a buttress or

presented below.

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

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