Electromagnetic-thermo-mechanical coupled modelling of microwave-assisted TBM disc cutting

Microwave irradiation is regarded as a promising technology to assist mechanical rock breaking for its substantial advantages in reducing cutter wear and enhancing rock fracture. Due to the high cost of laboratory experiments and field tests, numerical simulation has become the primary method to investigate key issues of microwave-assisted tunnel boring machine (TBM) cutting. In this work, an electromagnetic-thermo-mechanical coupled approach is developed to implement the numerical modelling of microwave-assisted TBM disc cutting. Different numerical methods are coupled in our model to exert their respective advantages, including the electromagnetic-thermal solution of COMSOL, thermo-mechanical fracture simulation of the lattice spring model (LSM), and rock-cutter contact treatment of discontinuous deformation analysis (DDA). The conversion from the Euler to Lagrange domain is adopted to address the motion of the electromagnetic-thermal field in the disc cutting process. The proposed coupled numerical approach is first verified by the corresponding modelling of the microwave-irradiated rock experiment, in which the coupled approach can also provide the evolution process of three-dimensional spatial rock fracturing that is hard to obtain in the experiment. Implemented into the numerical full-scale rock linear cutting experiment, our coupled approach is further applied to simulate rock disc cutting assisted by microwave irradiation. Through the numerical results, it is concluded that a moving microwave irradiation is better for reducing the cutter normal force as a whole in the disc cutting process. For the moving microwave irradiation, the cutter normal force will decrease with the increasing microwave power or decreasing moving speed, in which the microwave power plays a more significant role when the total microwave energy input remains the same. Finally, the curve of average normal force reduction with the microwave energy input at the engineering scale is analysed based on the numerical results of our coupled model, which provides some insights and suggestions for the future practical application of microwave-assisted TBM tunnelling.