Abstract：By analyzing the effects of initial vertical geostress on plastic zone radius of circular underground tunnel，displacement changes in plastic and elastic zones of surrounding rock and bolt stress distribution mode，it is revealed that the initial vertical geostress is very important for reinforcement effect. The study results show that the stresses in elastic zone are related with the vertical geostress，but the stresses in plastic zone are opposite. With the vertical geostress increasing，the radius of plastic zone increases；and there is a nonlinear relation between the vertical stress and the radius of plastic zone. The radial displacements in plastic zone and the maximum displacement of tunnel wall increase with the increase of the vertical geostress. Based on the interaction between rock mass and rock bolt，the analytical constitutive equations of stress distribution of fully grouted rock bolt in surrounding rock of circular tunnel are built. On the basis of the model，the stress distribution mode of bolt under different vertical geostresses is analyzed. It is shown that the friction resistance and the axial load increase with the increasing vertical geostress，and stress concentration appears at bolt end more obviously. When the friction resistance at bolt end is more than the allowable shear strength of surrounding rock，the cracking failure happens in bolt and surrounding rock，which should be considered in design and construction. Finally，the method for improving the reinforcement effect when the anchor head cracks is put forward. It is suggested that setting plate can improve the reinforcement effect of fully grouted rock bolt.
