Design of fully grouted rock bolts – a reinforcement concept: analytical and numerical calculation

Abstract

Introduction. Among the common support systems in tunnelling and mining, rock bolts have been widely used to reinforce rock mass and also to reduce geological hazards. Furthermore rock bolts can be applied under varying different geological conditions with cost-effectiveness. Although different methods are developed for grouted rock bolts design until now, the interaction mechanism of the rock bolts and rock mass is still very complicated issue. Methods of research. The paper addresses a simple analytical model and numerical simulation for the analysis and design of fully grouted rock bolts based on the reinforcement principle. According to this concept the jointed rock mass reinforced by grouted rock bolts is considered as composite material which includes rock mass, the grout material and the bolt shank. The mechanical properties of this composite material depend on the ratio of the components. The closed-form solution was developed based on the assumption that the rock mass around a circular tunnel remained elastic after installing fully grouted rock bolts. Results. The main parameters of the rock-bolt system (the diameter and length of bolt shank, the space between the bolts) are then easily estimated from the obtained solution. For noncircular tunnel, the numerical simulation is performed to show how the design of rock bolts could be done by using numerical methods.