Page 252 - Rock Mechanics For Underground Mining

EXCAVATION DESIGN IN STRATIFIED ROCK

Figure 8.9 Flow chart for the deter-
mination of stability and deflection of
a voussoir beam (after Diederichs and
Kaiser, 1999a).

value (Martin, 1997). For foliated and many sedimentary rocks, the rock fabric is
characterised by a plane of weakness parallel to the main structural features. The
theory for the strength of a rock mass containing a single set of uniformly oriented
planes of weakness is presented in Chapter 4. It indicates that a small inclination
of the planes of weakness to the direction of the major principal stress results in a
significant reduction in the compressive strength. Thus a prudent evaluation of the
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