Failure response and beam effect of bolt reinforced layer: Numerical modelling using FDM-DEM coupling method

Bolts reinforcing surrounding rock is a common reinforcement method. In this paper, through finite-discrete element coupling numerical simulations and model tests, the beam effect within the bolt reinforcement layer (BRL) is visualized, and the failure response of the overall BRL is investigated. First, a finite-discrete element (FDM-DEM) coupled numerical model is developed to conduct loading failure tests on BRL. Second, model tests are conducted to validate the FDM-DEM numerical model, which exhibits concordance with the failure location, evolution process, failure load (6F), and ultimate load (6U) of experimental results observed in BRL. While BRL without bolt reinforcement (BRLW) presents a "fragmentation" failure, BRL exhibits a comprehensive deformation failure owing to the beam effect, characterized by minor rockfalls of the tunnel crown. Finally, a parameter analysis was conducted to investigate the impact of bolt length (Lb), bolt spacing (Bs), and bolting range (Br) on the failure response and beam effect of BRL. The results suggest that the increase of Lb and Br and the decrease of Bs will each strengthen the beam effect of BRL, consequently enhancing the 6F and 6U.