Abstract: In this study, the implicit cylindric anchor bar element is adopted to simulate the bonding rock bolt in the large underground caverns. Then an additional stiffness model of the anchor bolt attached to the surrounding rock is established. According to the neutral point theory, the differential equation of load transfer relating to the interaction between the surrounding rock and the bolt is deduced, by assuming the shear slip model on the interface of anchorage bolt body. Based on the discrete displacement of surrounding rock obtained by 3D elastoplastic finite element incremental method, the continuous displacement of surrounding rock which causes the deformation of bolt is acquired by using the interpolation and curve fitting. Furthermore, the distribution functions of the axial load and the shear stress on the interface between the bolt and surrounding rock are obtained by solving the differential equation. The shear stress is transformed into the equivalent additional stress acting on the rock mass, and thus the supporting effect of the bolts can be reflected. This case analysis shows that the new algorithm can be well used to simulate the supporting effect of bolts. It is also found that the anchorage stress distribution obeys the neutral point theory. As a result, the function of shear stress on the interface between the bolt and surrounding rock can be divided into positive part and negative part by the neutral point, and the axial load distribution of bolt is a unimodal curve. In addition, the calculated values by the new method show good agreement with the measured values.

Key words: underground caverns, implicit anchor bar, neutral point theory, deformation of surrounding rock, anchoring effect