Effect of microwave-induced fracturing of Chifeng basalt by a multi-mode cavity

The microwave-induced fracturing of rock as a promising microwave-assisted mechanical rock breakage technology and can release the stress on a rock mass in deep underground projects. It is of significance to the construction efficiency and safety of underground projects. In a relatively short period of time (tens of seconds or minutes), microwave irradiation can cause rocks to be fractured or even melted. Two cylindrical basalt samples are irradiated by microwave at different powers using a frequency 2.45 GHz multi-mode resonator. The temperature distribution on the surface of the samples at different time is measured by an infrared thermal imager to obtain their heating characteristics during microwave irradiation. The microwave-induced fracturing effect of rock samples is evaluated by rock strength and wave velocity, the mechanism of microwave fracturing rock is expounded by dielectric properties and microscopic characteristics, and the influence of microwave irradiation on the Protodyakonov coefficient and rock crushing work ratio of rock is studied. The results show that the surface temperature of the samples is distributed in a regional non-uniform way, and the temperature at a certain point on the sample increases linearly with the irradiation time. The rock strength and wave velocity decrease linearly with the microwave irradiation time. Pyroxene (a mineral with strong microwave absorption) produces a large amount of heat after absorbing microwave, and olivine (a mineral with strong thermal expansion) produces a strong thermal expansion under the action of high temperature, resulting in great microwave fracturing effect of Chifeng basalt. After microwave irradiation, the Protodyakonov coefficient and rock crushing work ratio decrease to a certain extent. The higher the microwave power and the longer the irradiation time, the greater the degree of reduction of the Protodyakonov coefficient and the crushing work ratio of the rock.