This chapter presents the determination of design block for tunnel supports in highly jointed rock mass. For an underground excavation through a competent and discontinuous rock mass, a preferred block failure can be expected with particular boundary joint orientations and half-space combinations. This block can be found analytically by using the rock mass discontinuity distributions, the rock mass spacing distributions, and the procedures and methods of block theory. The three major factors that contribute to the block failure are the frequency of its boundary planes in the rock mass, the shape of its joint pyramid, and the instability of its joint pyramid. Block theory is established as a relevant and powerful tool for assessing the influence of discontinuities and tunnel geometry on design factors. The design block for an opening can be found prior to actual construction on the basis of the geological mapping or exploration data at hand. A great variability in joint orientations can be handled by introducing more joint sets to the system.
|Title of host publication||Analysis and Design Methods|
|Subtitle of host publication||Principles, Practice and Projects|
|Place of Publication||Oxford|
|Number of pages||30|
|State||Published - 1993|