Simulating the effect of disc erosion in TBM disc cutters by a semi-infinite DDM
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ORIGINAL PAPER
Simulating the effect of disc erosion in TBM disc cutters by a semi-infinite DDM Hadi Haeri & Mohammad Fatehi Marji & Kourosh Shahriar
Received: 20 March 2014 / Accepted: 23 May 2014 # Saudi Society for Geosciences 2014
Abstract 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
H. Haeri (*) Department of Mining Engineering, Bafgh Branch, Islamic Azad University, Bafgh, Iran e-mail: [email protected] H. Haeri e-mail: [email protected] M. F. Marji Mine exploitation Engineering Department, Faculty of Mining and Metallurgy, Institution of Engineering, Yazd University, Yazd, Iran K. Shahriar Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran, Iran
generate the curvature of the cutter tip, which in turn reduces the cutting efficiency and increases required specific energy for a typical disc cutter. Keywords TBM disc cutters . Non-eroded and eroded models . Crack coalescence . HSDDM2D
Introduction One of the most complex rock excavation problems is the indentation and cutting actions of the mechanical tools such as disc cutters of tunnel boring machines (TBM). A widespread application of rock fracture mechanics in studying the mechanism of cracks propagation and cracks coalescence associated with the rock cutting of mechanical tools in mining and civil engineering projects have been reported which indicates the significance of the chip formation process in rocks underneath the TBM disc cutters (Rostami and Ozdemir 1993; Gong et al. 2006; Zhao et al. 2007; Acaroglu et al. 2008; Gong and Zhao 2009; Cho et al. 2010; Bilgin et al. 2012). The key parameters in TBM head design are head diameter, number of cutters, thrust force, rolling force, RPM, penetration depth, and cutter spacing (Rostami and Ozdemir 1993; Acaroglu et al
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