Numerical Simulation of Particle Size Influence on the Breakage Mechanism of Broken Coal

The goaf is generally consisted of broken coal and rock mass. During the process of overburden strata subsidence and compaction, the broken characteristics directly affect the mechanism and pore characteristics of the caving coal and rock mass. In order to study the influence of particle size on the breakage mechanism of broken coal in the compaction process, the bonded particle model of broken coal sample was carried out to study the breakage characteristics during the compaction with different particle sizes. The stress-strain model of the broken particle model (BPM) during compaction was given. The particle size affects the maximum vertical strain,epsilon(m), and the stress-strain curve at the beginning of loading. But the particle size has no effect on the slope of the stress-strain curve in linear stage. During the compaction process, the porosity of the BPM can be divided into three stages: slow decrease stage, accelerated decrease stage and slow decrease stage with the increase in strain. Particle size also affects the change in porosity during compaction. The larger the particle size is, the smaller the porosity is at the same strain, but the particle size has no effect on the porosity-stress curve. The breakage rate of BPM increases in S-shape with the increase in strain. When the strain of BPM is over the maximum vertical strain, the particle is basically no longer broken. The larger the particle size is, the larger the residual particle cluster size will be when the breakage rate is stable. The particle sizes' influence on the evolution characteristics of BPM mechanical properties, porosity and breakage rate was demonstrated. The numerical simulation results in this paper can be used for analyzing the compaction characteristics of caving zone at the engineering scale.