Further examples of rock mechanics interaction matrices 23514.6 Further examples of rock mechanics
interaction matrices
The three modes of fracturing rock to produce a discontinuity are shown
in Figs 2.15-2.17. In these figures, the modes are shown in isolation, although
it may well be that the prevailing stress state at a given location is such that
the mode of failure is a hybrid of one or more of these fundamental modes.
In an attempt to understand the hybrid modes, an interaction matrix can
be drawn in which the fundamental modes are placed on the leading
diagonal. This is shown in Fig. 14.13-in which we have assumed, for the
purposes of illustration, that there is no path-dependency. Also, in the
sketch shown below the matrix, all three modes occur simultaneously.
In Fig. 14.14, there is a related matrix in which the leading diagonal terms
are normal, wrench and thrust faults, as dictated by the relative magnitudes
of the three principal stresses causing the faulting. In this case, the presence
of one type of fault will perturb the local in situ stress field, with the result
that it could be reactivated as a different type of fault: the principal stresses
will have changed and there will have been path-dependency introduced
into the off-diagonal, double-faulting, elements.
Mode1+2+3Mode 1 + 3Mode 2 + 369 Mode 3
Figure 14.13 Unary, binary and ternary combinations of the fundamental modes
of rock fracture.