Engineering Rock Mechanics

Questions and answers: design of surface excavations 335

available friction angle

x-coordinate, m

-15 \lo -5 /$ 5 10 15 20 25 30

-40.0'

Overall, we can conclude that the stability of the dam will be marginal.

Firstly, the negative radial stresses to the left of the dam will not be

sustainable (as the tensile strength of bedding planes can be taken to be

zero). Secondly, slip will take place in the region to the right of the dam

where the frictional strength of the bedding plane is exceeded. Although

a more sophisticated analysis may show that the dam is, theoretically,

stable, we must never forget that the consequences of instability in a

structure such as a dam will usually be catastrophic.

418.10 Using the principle of virtual work, determine the value of P

for limiting equilibrium for the foundation shown below.

A18.10 We start by drawing a free body diagram of the entire found-
ation, and mark vectors representing the virtual displacements taking
place on the various block boundaries.

P

\

W

I

\ B +

E

30" ,,