Page 236 - Rock Mechanics For Underground Mining

EXCAVATION DESIGN IN MASSIVE ELASTIC ROCK

Figure 7.19 Problem geometry for necessary to consider other mechanisms to explain the mode of action of support and
determining the effect of support reinforcement systems.
load on the elastic stress distribution The following example is intended to illustrate the main features of the function
around an elliptical opening.
of surface support on excavation peripheral rock, and is based on an analysis by
Ladanyi (1974). It is not a basis for comprehensive description of the interaction
between installed support and tunnel peripheral rock, which is a more complex,
statically indeterminate problem. The problem geometry is shown in Figure 7.20a,
with a circular opening excavated in a medium subject to hydrostatic stress. The field
stresses and rock mass strength are such that an annulus of failed rock is generated in
the excavation periphery. The main questions are the relation between the radius, r e ,
of the failed zone, the applied support presure, p i , and the stress distribution in the
fractured rock and elastic domains. It is assumed that the strength of the rock mass is
described by a Mohr–Coulomb criterion, i.e.

(1 + sin ) 2c cos
1 = 3 +
(1 − sin ) 1 − sin
or

1 = b 3 + C 0 (7.9)
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