Experimental study on mechanical properties and damage mechanism of self-stress grouted crushed coal of different grain sizes

Abstract

The reinforcement mechanism of self-stress grouted crushed coal of different grain sizes is not clear. In this study, crushed coal of 5∼10, 10–20 and 20∼30 mm grain was selected. It obtained that the grain size was proportional to the width of sedimentary fissure among coal blocks and inversely proportional to its distribution range. As coal grain size increases, the uniaxial compression strength (UCS) of grouted specimens decrease and the AE parameters increase, respectively. The slurry forms a mesh skeleton structure in the 5∼10 mm specimen, significantly increasing its bearing capacity. However, in the 20∼30 mm specimen, the porous coal block is the main carrier, reducing the bearing capacity. Swelling needle-like Aft crystals produced closely occludes the coal, increasing the binding ability and overall compactness; almost none of the coal-slurry intersections are damaged during uniaxial compression. The main damage areas of 10∼20 mm and 20∼30 mm grouted specimens are inside coal by SEM, and the cracks increase with the rise of coal grain size. The trends of damage variable and cumulative energy counts curves are approximately the same, further confirming the reliability of the analysis of the AE experimental results. This paper can lay the foundation for theoretical research and field practice of self-stress grouting reinforcement.