Study of mechanical model of fully grouted rock bolt's anchorage interface in tunnel surrounding rock

It is of great importance for studying mechanical effect of initial support system in tunnel engineering when analyzing distribution and variation of fully grouted rock bolt's stress in elastoplastic surrounding rock. A bolt's axial displacement differential equation is established according to the stress equilibrium in a small section of a rock bolt and the shear stress transfer mechanism of anchorage body interfacial layer between rock bolt and surrounding rock. Then the axial load distribution function and the shear stress distribution function on the interface of the fully grouted bolt are obtained by solving the differential equation under the interaction between rock bolt and surrounding rock mass. The reaction of the shear stress on interface of the fully grouted bolt on the surrounding rock is assumed to be symmetric radial action. The plastic zone radius of circular tunnel for bolt-shotcrete support can be solved by means of Mohr-Coulomb yield condition. On the basis of the model and function above, the mechanical effect of system for surrounding rock and initial support is analyzed. According to the analysis of example, it is shown that selection of supporting time has great influence on anchoring effect and surrounding rock stability. It is suggested that increasing the thickness of the grouted layer properly can decrease efficiently shear stress concentration at bolt end and also can improve the reinforcement effect of fully grouted rock bolt.