In some circumstances it may be appropriate to include downstream
passive wedge resistance, Pp, as a further component of the total resistance
to sliding which can be mobilized. This is illustrated in Fig. 3.6, and may be
effected by modifying equation (3.22) accordingly:
FSF(SPp)/∑H (3.26)
where
PpWwtan() (3.27)
andWWis the weight of the passive wedge, as shown.
In the presence of a horizon with low shear resistance, e.g. a thin clay
horizon or clay infill in a discontinuity, as illustrated in Fig. 3.6, it may be
advisable to make the assumption S0 in equation (3.26).
With the normal load combination applicable, the shear friction
factor required in the foundation zone is generally FSF 4.0. On planes
within the dam and at the base interface, FSF 3.0 is representative. Values
cAAB
cos(1 tantan)
140 CONCRETE DAM ENGINEERING
Fig. 3.6 Sliding: weak seams and passive wedge resistance
