Use of indentation tests to study the influence of confining stress on rock fragmentation by a TBM cutter

This paper explores the influence of the confining stress on rock fragmentation under the cutter of tunnel boring machine (TBM) by indentation test. Acoustic emission (AE) system was employed for real-time monitoring the rock fragmentation process during the indentation test. Granite and marble samples were used in the indentation test. The rock fragmentation processes with the different confining stress levels was studied based on the characteristics of force-penetration depth curve and the AE parameters, including AE energy rare, hit counts, amplitude and location of AE events. After the indentation test, the rock samples were cut along the centerline of rock samples and subsequently the crack distribution and the size of crushed zone were measured. The test results showed that the force for crack initiation and crushed zone size increased with increasing confining stress. The cracks tend to propagate to the free surface as the confining stress increases. But for the marble samples, there exists a critical confining stress condition, such that if the confining stress is more than the critical value, the force for crack initiation and crushed zone size decrease dramatically. Moreover, it was found that rock slabbing induced by confining stress had occurred before TBM cutter indentation. Such confining stress condition promotes rock fragmentation. (C) 2014 Elsevier Ltd. All rights reserved.

[1]  Emmanuel M Detournay,et al.  Intrinsic Length Scales in Tool-Rock Interaction , 2008 .

[2]  J. Labuz,et al.  Indentation of rock by wedge-shaped tools , 2006 .

[3]  Hongyuan Liu,et al.  Numerical simulation of the rock fragmentation process induced by indenters , 2002 .

[4]  Bernardino Chiaia,et al.  Fracture mechanisms induced in a brittle material by a hard cutting indenter , 2001 .

[5]  Leon Mishnaevsky,et al.  PHYSICAL MECHANISMS OF HARD ROCK FRAGMENTATION UNDER MECHANICAL LOADING: A REVIEW , 1995 .

[6]  B. Stimpson,et al.  Identifying crack initiation and propagation thresholds in brittle rock , 1998 .

[7]  Emmanuel M Detournay,et al.  Discrete element modeling of tool‐rock interaction II: rock indentation , 2013 .

[8]  Emmanuel M Detournay,et al.  An Analytical Model for the Indentation of Rocks by Blunt Tools , 2000 .

[9]  A. Boniface,et al.  Tunnel Boring Machine performance in basalts of the Lesotho Formation , 2000 .

[10]  M. Hood,et al.  Observations of crack growth in hard rock loaded by an indenter , 1984 .

[11]  A. Markus.  The Lotschberg Base Tunnel Connecting Europe , 2002 .

[12]  Jian Zhao,et al.  Development of a rock mass characteristics model for TBM penetration rate prediction , 2009 .

[13]  Claudio Oggeri,et al.  Laboratory tests to study the influence of rock stress confinement on the performances of TBM discs in tunnels , 2011 .

[14]  Jian Zhao,et al.  Numerical modelling of the effects of joint spacing on rock fragmentation by TBM cutters , 2005 .

[15]  E. Detournay,et al.  Normal Wedge Indentation in Rocks with Lateral Confinement , 1998 .

[16]  Claudio Oggeri,et al.  Experimental and Numerical Studies on Rock Breaking with TBM Tools under High Stress Confinement , 2007 .

[17]  Hongsu Ma,et al.  Numerical study of the effect of confining stress on rock fragmentation by TBM cutters , 2011 .

[18]  Jian Zhao,et al.  Rock burst and slabbing failure and its influence on TBM excavation at headrace tunnels in Jinping II hydropower station , 2012 .

[19]  Soo-Ho Chang,et al.  Estimation of cracking and damage mechanisms in rock under triaxial compression by moment tensor analysis of acoustic emission , 2004 .

[20]  N. A. Chandler,et al.  The progressive fracture of Lac du Bonnet granite , 1994 .

[21]  P. Kaiser.  ROCK MECHANICS CONSIDERATIONS FOR CONSTRUCTION OF DEEP TUNNELS IN BRITTLE ROCK , 2006 .