Evaluation of TBM disc cutter wear issue in hard rock tunneling; a case study

The research project in this study is a part of a 36 kilometer tunnel with 6.32 m in diameter for conveyance of water from the western of Zagros to the Uromia Lake that is under construction through hard rock by using of two tunnel boring machines. Lithology of the tunnel alignment including of granite, granodiorite, hornfels, schist, limestone, dolomite, shale, slate and phyllite. The wear of cutting tools is one of the main challenges of the studied tunnel, which impact significant cost and serious delays on schedule. Wear can be defined as the continuous and unwanted loss and removal of material from the surface of a solid object, as e result of mechanical actions, such as contact and relative motion between two objects. Abrasive wear and impact wear are one of the most important type of wear occurs on the TBM disc cutters. In this paper field actual cutter wear data belong to 9.5 Km of the bored tunnel, geotechnical properties and laboratory information are used to study the wear phenomena. Field data show that abnormal wear of disc cutters with 51 percent is more than normal wear. Also the study of disc cutter consumption rate in relation the geological characteristics and TBM parameters show that the Cerchar abrasivity index (CAI) and uniaxial compressive strength (UCS) are in agreement with disc cutter consumption rate. The obtained results indicate that thrust, torque and penetration rate have a relatively good relation with disc cutter consumption rate. It was not found any relation between rock mass quality index, geological strength index and disc cutter wear rate. In general the relative cutter life in the studied tunnel is in accordance with the relation proposed after Bruland (1998).