Rock reinforcement design based on control of joint displacement — A new concept : Fuller, P G; Cox, R H T Paper to 3rd Australian Tunnelling Conference, Sydney, 12–15 Sept 1978, 8P

Abstract

This paper presents a design procedure for mechanical reinforcement of a rock mass. It is based on the concept that reinforcement should limit displacements at structurally weak regions of the rock mass (discontinuities) allowing a state of self support and a stable arch to develop in the rock immediately above an opening. In this design, the maximum load in the reinforcement occurs early in the stress relaxation phase. As relaxation progresses and open discontinuities are closed, the reinforcement load actually decreases. By deliberately designing reinforcement to ensure the creation of a stable rock arch, the dangers of large block falls will be minimized. Results of a theoretical approach to reinforcement of rock joints are presented in graphical form, highlighting the variables influencing the degree of joint reinforcement. An example of reinforcement design in a particular geological and stress situation is given to demonstrate the approach. Finally, field measurements from the NBHC mine at Broken Hill show development of a stable arch during stress relaxation and the consequent reduction in reinforcement load as the arch starts to develop.