Mechanisms of rockbolt support in jointed rock masses

Abstract

Rockbolts are relied on as a key component of underground mining support systems, and have been the subject of ongoing research over several decades. However, in spite of their extensive use and the research, the interaction mechanisms between the rockbolt and the rock mass in jointed rock structures are still not fully understood. In addition, the actual work that rockbolts perform under stress, as well as the way they deform across joints, has not been completely captured nor explained. In an attempt to improve the level of understanding relating to the reinforcement mechanisms of rockbolts in jointed rock masses, physical models of tunnels in simulated rock masses were constructed. The models represented a sedimentary rock mass with continuous bedding planes, and cross joints between the bedding. Different bedding dips were considered. 'Rockbolts' were installed to provide support to the tunnels. The models were subjected to lateral or vertical boundary deformations, or a combination of the two. Careful observations and photographic records of rockbolt behavioural mechanisms, as well as rock mass structural failure modes, were captured. Instability in the model tunnels was a function of the bedding dip, increasing with an increase in the dip angle. Instability was greatest in models in which the bedding orientation was greater than 45°. In these models, rockbolts were effective as support only when block movement or rotation was restricted. However, the rockbolts were found to be very effective in supporting horizontally layered jointed structures. Rockbolts were observed to attract loads due to rock mass movements. In resisting deformation, they were subjected to combinations of shear, bending, compressive and tensile loading. Rockbolt length and spacing were confirmed as important parameters in improving tunnel stability.

Analysis and prediction of brittle failure in rock blocks having a circular tunnel under uniaxial compression using acoustic Emission technique: laboratory testing and numerical simulation

“…The effects of joint on the stability of tunnels have been appreciated by mechanical analysis, numerical simulation [7,8], and physical modelling technique [9,10]. Jia and Tang [8] numerically investigated the influence of joint dip and the lateral pressure coefficient on the stability of tunnel in a jointed rock mass and reported different failure modes in tunnels.…”

“…Wang and Huang [7] also reported that joint sliding failure and shear deformation is mainly responsible for the joint-induced anisotropic deformation surrounding a tunnel. Moyo and Stacey [9] have developed a small scale 2D jointed rockmass tunnel physical model to observe the tunnel boundary deformation process. They reported that, in highly jointed rockmass, there is a significant movement across the joints.…”