ABSTRACT:

Excavation design, blast design and reinforcement design are interrelated processes. These design processes and the procedures that integrate them are termed Excavation Engineering. Excavation Engineering may be simplified in some circumstances by adopting simple models for the rock mass regime and using simple assessment procedures to study the effect of one process on another. In jointed rock, Block Theory offers a particularly attractive opportunity for studying the interrelationships between the different processes. The amalgamation of Block Theory with Excavation Engineering may be achieved using a diagram called an Isoplethogram. This diagram displays aspects of the block assembly that affect excavation engineering.

1 INTRODUCTION

The design of a mine or civil excavation requires consideration to be given to a multiplicity of interactions between various design constraints. In mining engineering an optimal design seeks to maximise extraction and blast efficiency and to minimise dilution, overbreak and the requirements for reinforcement or support. This usually requires cyclical treatment of the excavation design, the blast design, and the reinforcement design processes in a relatively complicated engineering procedure. These design processes and the procedures that integrate them are termed Excavation Engineering (Windsor et al, 1995). Excavation engineering may be simplified in some circumstances by adopting simple models for the rock mass regime and using simple assessment procedures to study different designs. A particularly tractable approach for jointed and stratified rock is to assume that the rock mass comprises an assembly of fully and partially formed blocks of rock. This has prompted the development of a number of block analysis techniques (e.g. Warburton, 1981, Goodman and Shi, 1995 and Priest, 1985) now generally known as 'Block Theory'. Block theory and some extensions (Windsor, 1992) may be used to study the interrelationships between the different design processes. However, in order to display these relationships a graphic device is required that displays the features of the block assembly. One possible candidate is termed an Isoplethogram.

2 THEISOPLETHOGRAM

An isoplethogram is a diagram that displays the isolines (or contours of the same magnitude) of a functional relationship that is directionally variant. A rock mass isoplethogram is a diagram displaying the isolines for a rock mass condition or feature that is, inter alia, a function of the orientation of a plane in the rock mass. Before exploring some isoplethograms associated with block theory it may be advantageous to briefly review the construction of an isoplethogram and how an excavation surface can be overlayed on the isoplethogram. In a spherical coordinate system, vectorial data may be represented completely using rotation in the horizontal and vertical planes to indicate orientation (representing dip direction and dip respectively) and radial distance to indicate magnitude. The tips of all unit vectors oriented in all possible directions produce the surface of a unit sphere called the reference sphere. Consequently, any plane intersecting the rock mass may be described on the sphere surface by its great circle, the pole of its upper or lower normal, or the point representing its line of maximum declination or inclination.

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