ABSTRACT: This paper addresses the challenges associated with using fully grouted rock bolts in shallow to moderate depth underground cavern design in laminated ground. Laminations in a rockmass have the capacity of being either an asset or challenge to a cavern design. If supported adequately the rockmass acts as structural beams in the roof which enable a stable large span excavation. Fully-grouted rock bolts can be used to support against layer dissociation due to displacement along the shear plane, where even minor movement can cause instability. The mechanisms affecting the effectiveness of the bolts are complex and understanding the interactions of the three materials (the rockmass, grout and steel bolt) are critical. Preliminary models of a fully grouted rock bolt in shear have previously been used to determine the viability of using three-dimensional Finite Difference Method (FDM) numerical modelling to represent the behaviour of bolts when sheared. In this paper, focus is therefore given to the individual effects of the various parameters influencing the efficiency of a rock bolt to support a beam undergoing shear: confining stresses, joint conditions, installed bolt angle and the thickness of the grout annulus.
1. INTRODUCTION Shallow excavations through layered or laminated ground, including sedimentary rock and jointed rock units, can often pose challenges when designing large span underground spaces. However, if careful attention is given to the natural structure of the rock, the layers can act as a stable structure or beam within the roof of the excavated region. By reducing the dissociation of layers within the rockmass, the inherent stability of excavations through the heterogeneous material is greatly increased. In many such geomechanical applications, rock bolt systems are used to support and reinforce rockmasses. Two primary types of rock bolts exist: active bolts and passive bolts.