Simulating the effect of disc erosion in TBM disc cutters by a semi-infinite DDM

Underground excavation in rocks can be accomplished in several steps. The cutting action of mechanical tools such as disc cutters used in tunnel boring machines (TBM) is one of the most basic steps. Indentation of TBM disc cutters into the rock can produce rock chips in different scales. This phenomenon involves the production of micro cracks, their propagating, and coalescing process to form macro cracks. The present research focuses on the concepts of linear elastic fracture mechanics (LEFM) and maximum tangential stress criterion to investigate the micro crack propagation and its direction of growth in rocks underneath the TBM disc cutters. A modified higher order semi-infinite displacement discontinuity method (HSDDM) with third order displacement discontinuity elements (cubic elements) is used to estimate the stress intensity factor in the fractured rocks underneath a single disc cutter. To reduce the errors caused by stress and displacement singularities near the crack tip, three special crack tip elements have been implemented in the HSDDM2D computer code. TBM disc cutters will be eroded after a period of working. Therefore, the numerical simulation of eroded and not eroded discs has been proposed in this study. To simulate the eroded disc, four small elements have been modeled to generate the curvature of the cutter tip, which in turn reduces the cutting efficiency and increases required specific energy for a typical disc cutter.