Effect of pretensioned stress to rock bolting

Based on the analysis on existing problems of rock bolting for complicated and difficulty roadways,the importance of rock bolting stiffness,especialy the pretensioned stress to bolting effects was expounded.The distribution features of the stress fields caused by the pretensioned stresses of bolts and cables,and the effects of steel strip to the bolt pretensioned stress diffusion were analyzed through finite difference numerical modelling.The new concepts,such as the active supporting coefficient,the coefficient of strength utilization,the coefficient of pretensioned bolt length,the effective compressive zone,the coefficient of pretensioned stress diffusion,the framework and mesh structure of the effective compressive zone,and the critical supporting stiffness were put forward.The underground tests show that the deformation and roof delamination of roadway surrounding rock can be effectively reduced by means of great increase of the bolt pretensioned stress,the steel strip plays an important role in the rock bolting system,and there exsits a critical value for pretensioned stress,up to or beyond which the rock bolting can effectively control the deformation and damage of the surrounding rock.