A novel rockbolt formulation for a GPU-accelerated, finite-discrete element method code and its application to underground excavations

Abstract Rockbolting is widely used in civil and mining engineering to increase the inherent strength of the rock mass and reduce deformations around underground excavations. Rockbolt design by means of computer-aided numerical simulations has been playing an increasingly important role in geotechnical engineering. The research work presented herein introduces a novel rockbolt logic for the finite-discrete element method (FDEM), a numerical modelling approach capable of explicitly capturing brittle fracturing in complex geological media. Adoption of a GPU-based implementation was required to achieve substantial simulation speed-ups compared to conventional CPU computing. Rockbolts are discretized by 1D structural elements which are coupled to the solid finite element mesh by dedicated spring-slider connectors representing the bolt anchoring system. The formulation is verified by comparing simulated stress distributions with closed-form solutions for the cases of (i) a pull-out test on a fully-grouted rockbolt and (ii) a circular tunnel excavated in a bolted elastic medium. The effectiveness of the method for practical design applications is demonstrated by simulating the behavior of a bolted underground excavation in a heavily jointed rock mass. The effect of bolt spacing on the fracturing and deformational response of the rock mass is analyzed together with the force distributions in the rockbolts.