Analysis of the Combined Load Behaviour of Rock Bolt Installed Across Discontinuity and Its Modelling Using FLAC3D

Determining the rock bolt response under the typical in situ loading conditions of tension, shear and bending is an important part of the support design process. Calibrated numerical modelling can be an important tool for simulating the rock bolt response under in situ loads. However, currently available structural support models do not accurately model the rock bolt behaviour under shear loads. These models need to be modified to simulate the actual rock bolt response as determined under laboratory testing. Results from double shear laboratory tests by Kostecki (2019) have been used to calibrate the numerical models in ANSYS (ANSYS® Academic Research Mechanical 2019). The calibrated numerical models were used to study the state of stress along the rock bolt under different concrete strength. These numerical models are compared with the analytical model proposed by Pellet and Egger ( 1996 ). The results show that the rock reaction and consequently the shear load on rock bolt in the analytical model is underestimated (by up to 50% in case of high strength concrete). In high strength concrete, the yield and failure behaviour is determined by the shear stress rather than the bending and tensile stress as predicted by the analytical models. The analytical model is modified to better predict the shear forces in high strength concrete. The pile structural element available in FLAC3D (FLAC3D — Fast Lagrangian Analysis of Continua in Three-Dimensions 2017) finite difference method neglects the transverse shear strain in the element. In this paper, the pile structural element is modified to simulate the correct response of rock bolt under shear. The FLAC3D code is also modified to simulate the bolt yielding and failure under combined axial, bending and shear load. The modified model is validated with laboratory results from Mchugh and Signer (McHugh and Signer 1999) and is shown to be better at simulating the shear response and failure of rock bolt under shear compared to the original pile model.