Experimental study on confined compression deformation and breakage characteristics for different types of coal particles

Dynamic disasters such as coal and gas outburst seriously restrict the safety of mine production. Different types of coal particles reflect the coal structure, mechanical characteristics and energy storage behavior under load, which is of great significance to the study of coal and gas outburst disasters. However, there is little research on the coal particles breakage characteristics at present. In this study, raw coal and tectonic coal particles were selected to carry out confined compression experiments under different particle size distributions and stress conditions. The results show that the loading process is divided into slip stage, breakage stage and consolidation stage in turn. The deformation resistance of tectonic coal is weaker than that of raw coal in slip stage and breakage stage, but its strain hardening tendency is obviously stronger in compression stage than that of raw coal. Although the stress has a great influence on the relative breakage rate of coal particles, it has a weak influence at the consolidation stage. Due to the unstable structure of some coal particles in the middle particle size during loading, obvious particle size loss occurs after loading. At the same time, particle size distribution also affects the coal particle breakage. The relative breakage rate of large-size sample in single-graded sample group is higher and that of mixed-graded sample group is lower than that of single-graded sample group as a whole. Compared with the raw coal, the absolute breakage rate of large and medium size coal particles of tectonic coal is higher, and tends to break into smaller size coal particles during breakage process. The breakage degree of tectonic coal particles is always higher than that of raw coal. In general, strain hardening of tectonic coal particles is obvious, breakage degree is high, and even presents rheological characteristics in the experiment, which is the basic reason for low porosity and low permeability of tectonic coal. Moreover, most of the energy input to tectonic coal particles from outside is dissipated by friction, breakage and plastic deformation of coal particles, so the elastic energy stored in them is low.