Jian Zhao, Professor of Rock Mechanics and Tunnelling at Ecole Polytechnique Federale de Lausanne (EPFL), discusses some of the issues facing the use of hard rock TBMs to drive increasingly long tunnels through complex geology. Since the 1950's, developments in rock TBMs have been significant. New machine and material technology has greatly improved the capacity of cutters, as well as thrust and torque, permitting a TBM to deal with hard and abrasive rocks. Different TBM types, gripper, EPB, slurry, double shield, mixed shield and convertible shield, have been designed to suit different ground conditions. The TBM has technically reached a stage where a tunnel can be bored in almost any type of rock and ground, with reliability and performance comparable to that of other tunnelling methods.
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