A rock bolt and rock mass interaction model

An analytical model for rock bolts has been developed based on an improved Shear-Lag Model. The development of the model is based on the description of the interaction behavior of the rock bolt, the grout medium and the rock mass. On the basis of the model, the coupling and decoupling behavior of the rock bolt in pullout tests, uniform deformation the rock mass and intersecting joints are analyzed. The pullout test characteristic is described by the proposed model, and a back analysis method is proposed to calculate the shear strength of the interface media. For the rock bolts in a deformed rock mass, the influence of the installation time of the rock bolt has been taken into account, and the theoretical prediction is verified by the measured data. According to the proposed model, the position of the neutral point is not only related to the length of the rock bolt and the radius of a tunnel, but also is strongly influenced by the mechanical properties of the rock mass. Analysis of the joints intersecting the rock bolt shows that there may be more than one neutral point on the rock bolt, and the prediction of the simplified model is consistent with the pullout model. By using this model, a method is proposed to analyze the interaction behavior of the rock bolt and the surrounding rock mass, with a way of evaluating the supporting performance quantitatively. (C) 2004 Elsevier Ltd. All rights reserved.