SIMPLIFIED MODEL FOR WEAK ROCK TUNNELS CONSIDERING THE EFFECT OF SUPPORT PRESSURE DUE TO ROCKBOLTING WITH PLATE

The simplified model for weak rock tunnel is developed based on perfectly elasto-plastic concepts considering the effect of support pressure due to rockbolting with bearing plate. The model is verified by model tests in which we adopt axisymmetrical tunnel models with various bolting pattern (bolt length and circumferential and longitudinal bolt spacing) in artificial ground modeled on weak rock. The model proposed in this paper could be estimated the optimum bolt length and bolting pattern based on the allowable displacement of tunnel wall. The results of a series of test indicate that: i) the shear stress along the bolt acted as anchor length if the bearing plate set at the tunnel wall; ii) the support effect increased with the decrease of bolt spacing rather than bolt length within the test cases.