ABSTRACT:

A terminology for reinforcement practice is proposed based on the idea that a reinforcement device, a rock mass and a reinforced rock mass are all systems of components. It follows that the force displacement behaviour of each system is a consequence of the particular physical and mechanical characteristics of the system components and their interactions. Using this terminology a method is proposed for the design of reinforcement for excavations in jointed rock. The design method is based on identifying and stabilising all the blocks of rock that can form at the excavation boundary. It uses the early developments in block theory for identification and stability assessment of the blocks. These developments are supplemented with new reinforcement design and assessment procedures for the unstable blocks.

1 INTRODUCTION

Excavations are central to both mining and many civil engineering projects. For economic and safety reasons reinforcement forms an essential component of these projects. This is demonstrated by an estimated world wide usage of in excess of 500,000,000 reinforcement units per annum. Despite significant advances associated with reinforcement hardware, there is still conflict and confusion concerning the advantages and disadvantages of the different devices and their applicability to various rock engineering problems. This is thought to be due to the lack of a formal terminology in reinforcement practice and the lack of rational design procedures for the reinforcement of jointed rock. The art of rock reinforcement is still developing into a formal engineering discipline and therefore it will take time for the evolution of a formal terminology. However, it is suggested that some of the jargon in current use may be complicating and confusing what are in essence very simple but very important concepts of reinforcement practice. A terminology needs to evolve that includes terms to describe the range of reinforcement hardware, the techniques of applying that hardware to solve rock engineering problems and aspects associated with the installation and performance assessment of reinforcement. The behaviour of jointed rock is characterised by the nature and disposition of discontinuities. The discontinuities close to the excavation define the surface block assembly and influence its stability. Good support and reinforcement experiences are associated with addressing these instabilities local to the excavation boundaries rather than attempting to modify global instability induced by stresses. A rigorous engineering approach to rock reinforcement design for jointed rock is somewhat intractable because many of the parameters involved cannot be properly quantified. The design methods that take into account a basic rather than a detailed description of the rock mass are particularly popular. Two methods that follow this approach are the precedent design rules (e.g. Lang [1]) and rock mass classification methods (e.g. Barton et al. [2] and Bieniawski [3]). However, experience has shown that reinforcement is most effective under the low stress conditions that accompany surface block instability which leads to the belief that reinforcement schemes for excavations in jointed rock can be designed using a number of simple concepts based on the examination of the assemblage of surface blocks.

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