Study on Shear Mechanism of Bolted Jointed Rocks: Experiments and CZM-Based FEM Simulations

Shubo Zhang,Gang Wang,Xianlong Wu,Peng He,Junhong Yu,Genxiao Li,Yujing Jiang,Linlin Sun

doi:10.3390/app10010062

Abstract

Based on the underground jointed rock of the Huangdao water sealed oil depot in China, the shear failure mechanism of bolted jointed rock is studied through laboratory experiments and numerical simulation. Laboratory experiments are performed to explore the shear behavior of bolted jointed rock with different joint roughness. Our results show that using high strength bolts is beneficial to improving the shear strength of the jointed rock, but the high strength of bolts can also lead to the rock fracture, which should be avoided. For this particular project site, experimental results indicate that 15% elongation is the best. In addition, a new numerical simulation method with CZM (cohesive zone model) used for modeling the shearing process of bolted jointed rock is proposed. It can reasonably describe the characteristics of jointed rock as a discontinuous medium, and bolt as a continuous medium, that replicate well the shearing process. The numerical model is then verified by comparing the experiment results, and it can be effectively be applied to the simulation of joint shearing process. Finally, we use this simulation method to explore the shear failure mechanism of bolted joints, and find that the root cause of rock failure is the deformation mismatch between the bolt and the surrounding rock. The tensile stress between them eventually causes the rock to fracture near the bolt hole.

Highlights

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
Considering the discontinuity of the jointed rock and the continuity of the bolt, here we propose a new numerical method to simulate the shear of the bolted joints based on the laboratory experiments on the bolted jointed rock
Inorder ordertoto failure material parameters of theused bolt, it will lead to an increasethe in the contribution rate to the shearInstrength of change the elongation and strength, the plastic criterion is redefined according to the characteristics change the elongation and strength, the plastic criterion is redefined according to the characteristics the bolt, we reduce the yield strength of the material for the purpose of equivalent replacement

Summary

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. 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. Sten [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.

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Methods

Conclusion