Influence of joint roughness on the shear properties of energy-absorbing bolt

Abstract

Many experiments have been performed to study the mechanical behavior of rock bolts in resisting the shear force. However, almost all the tests were conducted on smooth rock joints, which is inconsistent with the field engineering practice. In this paper, the shear behavior of fully encapsulated rock bolts and energy-absorbing rock bolts inserted in the rough joints was investigated with a series of single shear tests under constant normal load (CNL) conditions. For all specimens, when the value of JRC increases gradually, the value of peak shear stress increases gradually. The ultimate shear displacement of an energy-absorbing rock bolt is larger than that of a fully encapsulated rock bolt for the same JRC condition, and they all decrease with the increase of JRC. The sensitivity of the energy-absorbing bolt to JRC change is lower than a fully encapsulated rock bolt. A dimensionless mathematical model was established to predict the ultimate shear displacement of rock bolts inserted in different roughness conditions. The ultimate shear displacement of the rock bolt was evaluated as a linear function of JRC. Two tests with natural rough joints were conducted to verify the applicability of the proposed empirical model for the natural rough joints. The predicted values of the ultimate shear displacement of rock bolts indicated good agreement with the test results. The proposed model is capable of providing an accurate evaluation of the ultimate shear displacement of rock bolts inserted in rough joints. The results of the laboratory test and mathematical model all show that the energy-absorbing bolt can bear a larger shear displacement and adapt to different joint roughness.