# Study on Shear Mechanism of Bolted Jointed Rocks: Experiments and CZM-Based FEM Simulations
## 1 Introduction  
As underground engineering projects are going deeper and deeper, especially in the fields of water conservancy, hydropower engineering, water sealed oil storage caverns, and deep resource exploitation [1; 2; 3; 4; 5], jointed rock is prone to causing instability of engineering structures and threatening the safety of engineering construction. Reinforcement by bolts has become one of the most effective and economical reinforcement technologies for the long-term stability of underground projects. Bolts play an important role in strengthening the surrounding rock, limiting the dislocation or slip between blocks, and effectively improving the stability of rock engineering structures. Among all types, the full-length bonded bolts have been widely used in various underground engineering projects [6; 7]. Significant achievements have been made in the study of bolted jointed rock, from both experimental and theoretical perspectives. [PERSON] [8] carried out an experimental study on full-length cement mortar bolts embedded in granite, and analyzed the impact of bolts on the shear strength of joints. [PERSON] [9] performed an experimental study and a theoretical discussion on the effect of bolts on the shear strength of joints. [PERSON] et al. [10] studied the reinforcement effect of anchor rod in rock mass with different properties through physical experiments, and found that bolts can significantly improve theshear strength of jointed rock mass. [PERSON] et al. [11] investigate the shear behavior of bolted rock joints with different roughness. Direct shear tests on both bolted and unbolted artificial joint specimens were conducted under various normal stresses. [PERSON] et al. [12] proposed the roughness parameters that considered that the anisotropic characteristic of joint roughness can capture the difference of roughness in forward and reverse directions along a single joint profile. The capacity to resist rock deformation is one of the important parameters affecting the shear strength of bolted jointed rock mass. [PERSON] and [PERSON] [13] established a new analytical model to predict the contribution of bolts to the shear strength of a rock joint, then compared the performance of this analytical model with experimental results to show its capability, and to describe the observed phenomena. [PERSON] [14] investigated the influence of bolt type on shear strength of rock mass for different rocks. However, there have been few studies on the influence of bolt elongation, bolt strength, and other factors on the reinforcement effect. Particularly given that a systematic study is lacking in evaluating and optimizing the bolted effect in practical engineering. The objective of this work is to conduct laboratory experiments to explore these influencing factors on the jointed rock, and explore the shear failure mechanism of bolted rock joints. With the advancement of numerical simulation, many scholars have explored the shear failure mechanism of bolted joints using different numerical techniques. [PERSON] and [PERSON] [15] used FLAC three-dimensional (3D) to study the influence of pre-stress on the shear behavior of joints. [PERSON] and [PERSON] [16] adopted the finite element method to simulate the joint direct shear tests, and the simulated results were in good agreement with the experimental results. However, the disadvantage of using the continuous medium theory to predict the deformation and failure mechanism of joints during loading is that it is not able to realistically reflect the breaking and weakening effects of rocks and joints. In order to simulate rock fracture process, some scholars have used the discrete element method, such as the Particle Flow Code (PFC) to perform the simulations. For example, [PERSON] et al. [17] proposed a new shear box genesis approach to overcome the unrealistic increase of shear strength and dilation angle in PFC. [PERSON] et al.