颗粒粒径对采空区破碎煤体压实破碎特征影响机制

Influence mechanism of particle size on the compaction and breakage characteristics of broken coal mass in goaf

煤矿采空区垮落带一般由破碎煤岩体组成,在垮落带压实过程中,破碎煤岩体的破碎特征直接影响着垮落带的物理力学性质及孔隙渗流特征。为了研究不同粒径破碎煤样压实过程中的破碎特征及其影响机制,构建了基于曲率半径与接触应力的颗粒材料屈服准则,进行了不同粒径破碎煤样的实验室压实试验与三维数值模拟研究。颗粒破碎准则表明影响颗粒破碎的主要参数为接触颗粒尺寸和接触颗粒的材料参数。得出垮落带相同压实应力条件下,破碎煤岩体尺寸越大,破碎煤岩体之间的接触应力越小。在实验颗粒粒径范围内,加载至相同应力状态下,颗粒粒径越大越不容易破碎,根据加载前后的级配数计算获得的破碎率越小。进而提出颗粒配位数(颗粒接触数)是加载过程中粒径对破碎率影响的主要原因。拥有较少配位数的小颗粒在传递相同应力的时候具有更大的偏应力进而导致相对于多配位数颗粒更容易破碎。加载过程中的量化模拟结果表明在初始粒径颗粒全部破碎时,3种粒径颗粒(10,15以及20 mm)中数量大于100子颗粒的占比分别为6.7%,24.6%,31.5%。随着破碎煤样的加载,不同粒径煤样最大颗粒对应的配位数不断增加,使得破碎煤样能够承受的应力远超过其自身强度。在颗粒配位数达到一定程度时,破碎煤样基本不再破碎,颗粒配位数基本保持不变。综合理论分析、实验室测试与数值模拟结果最终得出破碎煤样颗粒尺寸对破碎特征影响的主要决定因素是接触应力与配位数。在加载初期,破碎煤样配位数相差较小,破碎煤样尺寸越大,模型相同加载应力状态下的颗粒接触应力越小。在加载后期,大颗粒粒径的配位数要大于小粒径颗粒,使其更不容易破碎。

Caving zone is generally composed of broken coal and rock mass in coal mine goaf.During the compaction process of a caving zone,the breakage characteristics of broken coal and rock mass directly affect the physical and mechanical properties and pore and flow characteristics of the caving zone.The yield criterion of granular materials based on curvature radius and contact stress is constructed,and then the laboratory tests and three-dimensional numerical simulation are further carried out to study the breakage characteristics and the influencing mechanism of broken coal samples with different particle sizes during its compaction.According to the particle breakage criterion,the main parameters that affect particle breakage are the contact curvature radius and material parameters of contact particles.It is concluded that the larger the size of the broken coal and rock mass is,the smaller the contact stress between the broken coal and rock mass is.The experimental results show that within the range of experimental particle size,under the same stress state,the larger the particle size,the less likely it is to be broken,and the smaller the breakage rate calculated according to the gradation number before and after loading.Furthermore,particle coordination number(particle contact number)is proposed and is the main reason that determines the impact of particle size on breakage rate.Small particles with less coordination number have larger deviatoric stress when transmitting the same stress,which leads to easier breakage compared with particles with multiple coordination numbers.The quantitative simulation results also show that when the original large particles are completely broken,the proportion of sub-particles larger than 100 in the three kinds of particles(10,15 and 20 mm)is 6.7%,24.6%and 31.5%respectively.With the loading of broken coal samples,the coordination number corresponding to the largest particle of coal samples with different particle sizes increases continuously,which makes the stress that the broken coal samples can bear far exceed their own strength.When the coordination number reaches a certain value,the broken coal sample is basically not broken,the coordination number of the coal sample particles remains basically unchanged.Based on the results of theoretical analysis,laboratory test and numerical simulation,it is concluded that the main mechanism of the influence of particle size on the breakage characteristics is the difference between contact stress and coordination number.In the early stage of loading,the difference of coordination number is smaller,the larger the size of the broken coal sample is,the smaller the contact stress of particles under the same loading stress state of the model is.In the later loading process,the coordination number of large particle size is larger than that of small particle size,which makes it more difficult to break.