The caving zone in goaf can be regarded as a porous medium consisting of broken coal and a rock mass. During the compaction process of broken coal and a rock mass in a caving zone, the re-breakage of the rock and coal affects the compaction stress and pore characteristics of the caving zone. In this study, a discrete element numerical simulation of a broken coal sample based on the bonded particle model (BPM) was carried out to study the evolution characteristics of stress, strain, and breakage during its compaction. The grading equation of the minimum particle size during the simulation process is given based on a laboratory test. This equation can reduce the effect of the sub-particles, which cannot be further broken through the BPM. The stress–strain curve of the BPM during compaction can be divided into two stages using maximum vertical strain, ε_m, and the stress calculation model of these two stages is given. In first stage, there was no effect of the particle strength on ε_m. Here, ε_m of the BPM was equal to the porosity of the BPM minus the initial porosity of the broken particles. The average slope of a straight-line section after ε_m was proportional to the elastic modulus of the coal samples with a ratio of 1.0892. In addition, the particle breakage rate, B_s, and its calculation model were proposed to describe the breakage of the BPM during the compaction process. The evolution characteristics of particle breakage and its correlation with the stress, strain, and particle location are illustrated. The breakage rate of the model increased with increase in strain in an S-shape function. When strain was greater than ε_m, the particles had difficulty breaking again, and the breakage rates of soft coal, medium coal, and hard coal were 96.05%, 87.21%, and 87.78%, respectively. Under the same stress conditions, the breakage rate of soft coal was clearly higher than that of hard coal. The breakage rate increased the fastest when stress was equal to the tensile strength of the coal sample during the compaction process of the BPM.

中文翻译：

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破碎煤强度对采空区压实特性影响的数值模拟

采空区的崩落带可视为由碎煤和岩体组成的多孔介质。在崩落区破碎煤和岩体的压实过程中，岩石和煤的再破碎会影响崩落区的压实应力和孔隙特征。在这项研究中，基于键合颗粒模型（BPM）对破碎煤样品进行了离散元数值模拟，以研究压实过程中应力，应变和破裂的演化特征。根据实验室测试，给出了模拟过程中最小粒度的分级方程。该方程式可以减少子粒子的影响，而后者无法通过BPM进一步打破。利用最大垂直应变，压实过程中BPM的应力-应变曲线可分为两个阶段，ε_米，和这两个阶段的应力计算模型中给出。在第一阶段中，没有对粒子强度效果ε_米。在这里，ε_米的BPM的是等于BPM的孔隙率减去破碎颗粒的初始孔隙率。后的直线部的平均斜率ε_米是正比于煤样品与1.0892的比率的弹性模量。另外，颗粒破碎率B _s提出了其计算模型来描述压实过程中BPM的破坏。说明了颗粒破裂的演变特征及其与应力，应变和颗粒位置的关系。模型的破损率随着S形函数中应变的增加而增加。当应变比是大于ε_米，颗粒有困难再次打破，和烟煤，介质煤和硬煤的破损率分别为96.05％，87.21％，87.78和％。在相同的应力条件下，软煤的破碎率明显高于硬煤。在BPM压实过程中，当应力等于煤样品的拉伸强度时，破损率增加最快。