Experimental investigation on the influence of microwave exposure on the cutting performance of TBM disc cutter cutting of hard rocks

Microwave energy has been demonstrated to be able to assist mechanical rock breaking in geotechnical and mining engineering. The aim of this research is to study the influences of the interaction between microwave energy and rocks on the performance of disc cutters on a TBM (tunnel boring machine). By applying an open-type microwave-induced fracturing apparatus of hard rocks, cuboidal basalt samples were subjected to microwave irradiation for different times. Full-scale linear cutting tests were conducted on specimens subjected to microwave treatment on condition of having same penetration depth and cutting spacing. The results showed that high temperatures were mainly measured at the zone directly facing the microwave applicator and the surface temperature of the samples approximately increased in a quasi-linear manner with the duration of exposure to microwave irradiation. On condition of having a fixed penetration depth and cutting spacing, the amount of rock breaking by the TBM disc cutter increased with increasing exposure: the longer the exposure duration was, the more significant the fracturing effect of the samples. During cutting, the average normal and rolling forces applied to the disc cutter both linearly reduced with exposure time while the specific energy of the disc cutter for breaking rocks exhibited an exponential reduction relationship with exposure time. It can be seen that microwave irradiation can increase the amount of rock breaking by the disc cutter and reduce the cutting forces required by the cutter, thus further improving the efficiency of rock breaking with a TBM.