نوع مقاله : مقاله پژوهشی
1 دانشکده مهندسی معدن و متالورژی-دانشگاه یزد
2 دانشگاه آزاد
3 دانشگاه صنعتی امیرکبیر
عنوان مقاله [English]
Undoubtedly, one of the main accesses to the underground is indentation process. Indentation of TBM disc cutters into the rock are producing rock chips of small and big sizes and introducing the internal cracks in the rock. The present study focuses on the linear elastic fracture mechanics of rock and maximum shear stress criterion to investigate of crack propagation and its direction under disc cutters. Therefore displacement discontinuity method, which is a subset of the boundary element method, was used to model the crack propagation under blunted TBM disc cutters. In order to improve the accuracy and reduce errors in calculating displacement discontinuity in the Model, the higher-order elements (quadratic elements) to all boundary elements have been considered and also to prevent errors caused by stress and displacement singularity near the crack tip, three special crack tip elements, have been used. This method was used to determine the stress intensity factors (SIFs) in the rocks under single disc and twin discs of tunnel boring machine (TBM), whereas, disc cutters in the TBM will be eroded after a period of time. Therefore, the effect of blunting obtained numerically is compared with the values obtained from the laboratory results (linear cutting machine (LCM)) to verify the model. To simulate the bluntness model, we considered 4 small elements to generate the curvature of the cutter tip which reduces the computing efficiency and increases the required speciﬁc energy. To resolve this, we modeled a V-shaped cutter (constant cross section (CCS) - rigid disc cutters) of 432 mm in diameter and 80 mm in thickness.