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

Abstract

Faults are common water conduits in coal mines, with variable permeability based upon the extent of cracks along the fault plane. In this study, three samples from a fault were obtained from a mining area in Southwest Shandong, China to determine the geometric characteristics, including crack density, fractal dimension, and crack connectivity. For microstructural analysis of fault rock specimens, scanning electron microscopy (SEM), x-ray diffraction (XRD), and plane-polarized light microscopy tests were used, and the geometric characteristics were calculated. A nonuniformity coefficient that considers the mineral composition is proposed to describe the micro-crack network of fault rocks. The results show that there is a significant positive correlation among three geometric characteristic parameters, and the nonuniformity coefficient is positively correlated with those parameters of the crack network. The crack extension forms of the three fault rock samples are different, which is related to the different fracture toughness of the mineral particles. The optical photomicrographs and SEM images show that crack networks are most developed in the samples with the least clay content. There is a negative correlation between clay content and the geometric parameters of the crack network, which may be related to the friction coefficient of clay.