Method for predicting the microwave heating sensitivity of hard rocks: Application to microwave-mechanical excavation and microwave stress release in tunnels

Abstract

Accurate evaluation of the microwave heating sensitivity of hard rock in deep engineering, and its correlation with dielectric properties is crucial for predicting the microwave-mechanical rock breaking efficiency and assessing microwave-induced stress release effectiveness. Based on coaxial line transmission/reflection dielectric property test equipment, the dielectric properties of synthetic rocks made from different rock powders are tested, and the reliability of this method is verified. The dielectric properties and the microwave average heating rate of different rock minerals are tested, which provides the basis for the preparation of synthetic rocks. Taking engineering granite as an example, three main rock mineral powders are mixed thoroughly in different proportions, compressed into synthetic granite under 400 MPa to test their complex dielectric constant. A prediction model method for the dielectric properties of synthetic granite based on the mineral content is established. The research results indicate that the preparation pressure is positively correlated with the loss tangent of the sample and negatively correlated with the microwave penetration depth (D_p). The greater the D_p is, the smaller the loss tangent and the lower the microwave average heating rate of rocks. The classification standards for rock microwave heating sensitivity are discussed (microwave frequency of 2.45 GHz): strong sensitivity (D_p < 4 cm), moderate sensitivity (4 cm ≤ D_p ≤ 8 cm), and weak sensitivity (D_p > 8 cm). In engineering applications, the method for predicting rock microwave heating sensitivity provides a basis for selecting microwave parameters in different hard rock excavation areas or stress release areas.