Micro-CT experimental study of crack evolution of lignite under different temperatures

The crack evolution of lignite from 20°C to 600°C is studied by using micro-CT system intuitively. The extension and evolution of original cracks and new microcracks are discussed in detail. The study results show as follows: (1) From 20°C to 100°C, thermal cracking degree of lignite is moderate and just a few new microcracks initiate. (2) From 100°C to 300°C, thermal cracking is acute; many new microcracks initiate and original cracks extend quickly. The original and new cracks spread, overlap and connect with each other and finally form a crack network. (3) From 300°C to 500°C, the extension of microcrack is very slowly. (4) From 500°C to 600°C, some microcracks have trend of closure. With the increase in temperature, the microcracks initiate in soft coal along the bedding of coal seam and are arrested to hard coal; some cracks perpendicular to bedding direction will split on the edge of hard coal layer and then extend along the bedding of coal seam. The extension rate of cracks parallel to bedding direction is greater than that perpendicular to bedding direction.