Effects of sandstone mineral composition heterogeneity on crack initiation and propagation through a microscopic analysis technique

Abstract

Crack initiation and propagation are key scientific questions influencing rock failure. To study crack initiation and propagation during rock failure, CT scanning tests were performed on the sandstone samples. The initiation and propagation stages of sandstone cracks were analysed based on a reconstructed three-dimensional crack structure model. The types of crack initiation and propagation in minerals and the effects of mineral composition heterogeneity on crack initiation and propagation were studied using microscopic analytical techniques. The effect of mineral granularity on crack initiation and propagation was analysed using statistical methods. The results show that crack initiation and propagation can be divided into four stages: microcrack inoculation, mesocrack initiation, mesocrack evolution to macrocrack, and macrocrack penetration. Four cracks are formed at different locations, extending along the mineral edge, deflecting at the mineral edge, bifurcating at the mineral edge, and penetrating through the mineral. The poikilitic texture formed by quartz debris and cement makes it easy for cracks to extend along the mineral edges. In quartz debris with high crystallinity, the crack tends to deflect and bifurcate at the edge of quartz debris. The symbiotic structure of altered quartz and clay minerals easily causes cracks to propagate through the minerals. Furthermore, the distribution of mineral granularity affects crack initiation and propagation. The inhomogeneity of mineral granularity can easily cause the initiation and propagation of cracks. The size of the mineral granularity affects the width of the secondary crack. These research results can provide a basis and reference for predicting and evaluating the stability of rock masses.