Assessment of Ground-Support Interaction Using Continuum Grain-Based Models

ABSTRACT: Spalling of pillar ribs is a major hazard in the mining industry. Developing effective support guidelines requires an understanding of pillar damage mechanisms as well as the rock-support interaction. Bonded Block Models (BBMs) represent a convenient tool for this purpose, as they can reproduce the rock fracturing process reasonably well, but it is not known whether all variants of this modeling technique can replicate the impact of reinforcement (bolts) on otherwise unsupported ground. Broadly speaking, BBMs can be sub-divided into two groups: true discontinuum (implemented in DEM software) and pseudo-discontinuum (implemented in FEM software). Previous research by the authors has demonstrated the ability of DEM-based BBMs to reproduce rock-support interaction very well using real mining case studies. The current study is focused on evaluating the capability of FEM-based BBMs to replicate pillar damage mechanisms and rock-support interaction. Specifically, the stress-strain curves from BBMs developed in RS2 for three different width to height (W/H) ratio unsupported pillars (W/H = 1, 2, 3) were calibrated to match the macroscopic behavior of BBMs developed in UDEC, followed by analyzing the influence of rockbolt patterns in these models. Model outputs like stress-strain behavior, block and joint yield, and failure patterns were analyzed. With this, differences and similarities in the behavior of the two model variants have been discussed, considering their applicability in practical support design. 1. INTRODUCTION Pillars are an integral load bearing member in underground mines and play an essential role in upholding the functional integrity of the mine openings. As mining continues to progress deeper, these pillars are subjected to ever higher stresses, which increases the incidence and severity of ground control issues, including, but not limited to spalling, buckling, pillar bursting, etc. (Kaiser et al., 1996; Diederichs, 2007). From a macroscopic failure standpoint, the design of pillars is well-studied (Hedley and Grant, 1972; Krauland and Soder, 1987; Potvin et al., 1989; Lunder and Pakalnis, 1997; Martin and Maybee, 2000). On the contrary, design of surficial supports (e.g. rockbolts, wire meshes etc.) for controlling stress-induced failures at the pillar periphery remains a topic of research, primarily because of the complex interaction between support elements and unsupported ground undergoing stress-induced damage.