Stability of Slopes - Elements of Soil Mechanics - page 406

of column (5).
Columns 5 and 6 are now recalculated using F = 1.43 and a revised value of F is
obtained:

295 8
207 9

.
.

F = = 1 42 .

This is approximately equal to the assumed value of 1.43 and is taken as correct. Thus
the factor of safety of the slope is 1.42.
Had the assumed and derived values of F not been approximately equal, the iterative
procedure could have been repeated once again to find an improved value of F, as can
be demonstrated through the Example 13.4. xls spreadsheet.

Example 13.5: Bishop's routine method

Figure 13.21 gives details of the cross-section of an embankment. The soil has the fol-
lowing properties: φ ′ = 35°, c ′ = 10 kPa, γ = 16 kN/m 3 .
For the slip circle shown, determine the factor of safety for the following values of r u :
0.2, 0.4 and 0.6.
Plot the variation of F with r u .

Solution:

The calculations were based on the rigorous method and are shown in Fig. 13.22 and
Fig. 13.23.

Fig. 13.21 Example 13.5( a).