Quantification analysis of geometric characteristics of micro crack network on fault rock surface

Abstract

Fault is a common water conduit in coal mine, and the cracks of fault rock will greatly affect its permeability. In this study, three fault samples obtained in the mining area in Southwest Shandong of China was tested and observed by SEM, XRD and plane-polarized light microscope. The geometric characteristics, including crack density, fractal dimension and crack connectivity, of the crack network on the sample surface were calculated. Combined with the mineral content obtained by XRD, the nonuniformity coe cient of mineral composition in rock is de ned. The results show that the crack geometric characteristics of the three samples are quite different and the above geometric parameters of crack network on three fault rock samples are correlated. The optical photomicrographs and SEM images show that the crack network is developed most in the fault rock samples with the least clay content. The study suggests that the nonuniformity coe cient of rock samples is positively correlated with the geometric characteristic of crack network. The difference in the crack network of fault rock samples is related to the coe cient of friction of clay.Optical photomicrographs of fault samples: (a) one main crack (b) micro cracks which are circled in red