Permittivity and EM wave field of the stochastic broken rock and its applications

As a nondestructive method, GPR is widely used in detection the distribution of the broken rock zone surrounding laneways. For deep coal mining engineering, the rock surround laneways would experience several damages. The broken rock is a special composite medium by rock, fracture which is filled with water or air. Although, a lot of researches about the electromagnetism of rock have been done, mostly is about intact rock. And the EM wave field propagating in the stochastic broken medium was not clearly mastered too. Generally, it depends on empirical judgments to identify the boundary and determine the range of the broken rock zone. So, the authors try to establish a theoretical permittivity formula of the stochastic broken rock by analytical analyses, and the bulking factor of Rock Mechanics is introduced into the formula. Then, orthogonal numerical simulations, considering of fracture length, aperture, volume fracture number and moisture, are carried out to modify the theoretical permittivity formula. Furthermore, a numerical model of a laneway surround by a stochastic Broken Rock Zone(BRZ) is established, and the GPR profile along the inner surface of the laneway is calculated, which could be of help to identify the BRZ boundary in GPR profile. Engineering example of GPR exploration and borehole imaging are also given to illustrate the feasibility of GPR utilized on the BRZ detection in deep coal mining engineering.