ABSTRACT
Discrete Element Method (DEM) is considered as one of the best tools to explain the physics behind the experimentally observed facts of granular materials. This numerical technique considers the discrete nature of the granular materials /rock mass and adopts the use of force-displacement law and Newton’s laws of motion alternatively. It adopts an explicit finite difference method, which necessitates the use of extremely small time steps to ensure accuracy and numerical stability. The fundamental unit of DEM is the contact between two adjacent particles. The forces and displacements developed at the contacts help to characterize the micro-mechanical behavior, which is otherwise impossible to capture. The averaging of this behavior over the entire model helps to figure out the macroscopic response of the modeled assembly. By introducing a bonding concept, particles can be bonded together at contacts to reproduce the cementation effect similar to the cohesive strength of the rock masses. The study of the strength and behavior of weak cemented rock is one of the major thrust areas in rock mechanics and engineering. Generally, sedimentary rocks belong to the group of weak rock mass. They consist of rock fragments and minerals held together by natural cementing materials. The low strength and high deformability of these materials result in unexpected material behavior including yielding, squeezing, swelling etc. But, due to the practical difficulty in understanding the mechanical behavior of rock masses through physical experiments, numerical modeling has evolved as an efficient and practical tool in the field of rock mechanics. In this paper, the fundamental principles of DEM and the various micro-parameters associated with it are explained. The various issues related to the modeling of the particulate material are highlighted along with its solutions. Following an outlook into the methodology and numerical modeling steps, an underground weak cemented rock mass is modeled. The behavior of a single underground tunnel subjected to various structural and loading conditions are also added to furnish the utility of this numerical method in understanding and explaining the various mechanical phenomena from the fundamentals. The case study of a vertical cliff modeled adopting bonded systems and is subjected to non-uniform weathering is also presented to understand the application of DEM in cemented systems.
