In most rock engineering projects, a fully grouted rockbolt system is the primary support for reinforcing unstable rock strata. A better understanding of the characteristics of the load transfer mechanism between rockbolts and rock mass could lead to a significant improvement in the performance of rockbolts. Previous studies have pointed out that the bond-slip relationship between rockbolts and the rock mass is nonlinear and hence the bond-slip model in Fast Lagrangian Analysis of Continua (FLAC2D) could not adequately represent the nonlinear behaviour of rockbolts. In this study we numerically modelled the behaviour of fully grouted rockbolts subjected to tensile loads by implementing a nonlinear bond-slip relationship for the bolt-grout interface into FLAC2D. The proposed numerical model was verified by pull-out tests on rockbolts. The findings show that the modified rockbolt model in FLAC2D is capable of capturing the nonlinear shear bond stress behaviour.

INTRODUCTION

In many engineering projects, especially underground excavations, a fully grouted rockbolt system is the primary support used to reinforce unstable rock strata. A better understanding of the characteristics of the load transfer mechanism between rockbolts and the rock mass could lead to a significant improvement in the performance of rockbolts. Various studies have been conducted to investigate the load transfer mechanism of rockbolts (Benmokrane, Chennouf, and Mitri, 1995; Aziz, 2004; Ren et al., 2010; Ma, Nemcik, and Aziz, 2013; Nie et al., 2014a, 2014b; He, An, and Zhao, 2014; Martin et al., 2011a; Martin, Tijani, and Hadj-Hassen, 2011b; Ivanovic and Neilson, 2009). Benmokrane, Chennouf, and Mitri (1995) carried out a series of bolt pull-out tests and found that the relationship between the interfacial shear bond stress and the relative slip between the bolt and grout is not linear, as schematically shown in Figure 1. The term ‘bond-slip relationship’ is used to represent the relationship between the bond stress and the slip. The bond-slip relationship could significantly impact on the performance of fully grouted rockbolts under axial loading. Ren et al. (2010) and Martin, Tijani, and Hadj-Hassen (2011b) presented their respective analytical models in which a trilinear bond-slip relationship was considered. Ma et al. (2014) proposed an analytical bolt model based on a nonlinear bond-slip relationship. These analytical models are able to predict the mechanism of interfacial bond weakening of rockbolts.

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