The size distribution of the broken top coal blocks is an important factor, affecting the recovery ratio and the efficiency of drawing top coal in longwall top coal caving (LTCC) mining panel. The standard deviation of top coal block size (δ_t) is one of the main parameters to reflect the size distribution of top coal. To find the effect of δ_t on the caving mechanism, this study simulates experiments with 9 different δ_t by using discrete element software PFC. The δ_t is divided into two stages: uniform distribution stage (UDS) whose δ_t is less than 0.1 (Schemes 1–5), and nonuniform distribution stage (NDS) whose δ_t is more than 0.1 (Schemes 6–9). This research mainly investigates the variation of recovery ratio, drawing body shape, boundary of top coal, and contact force between particles in the two stages, respectively. The results showed that with the increasing δ_t, the recovery ratio of the panel increases first and then decreases in UDS. It is the largest in Scheme 3, which mainly increases the drawing volume at the side of starting drawing end. However, the recovery ratio decreases first and then increases quickly in NDS, and it is the largest in Scheme 9, where the drawing volume at the side of finishing drawing end are relatively higher. In UDS, the major size of top coal is basically medium, while in NDS, the size varies from medium to small, and then to large, with a distinct difference in shape and volume of the drawing body. When the major size of top coal is medium and small, the cross-section width of the initial boundary of top coal at each height is relatively small. Conversely, when the top coal size is large, the initial boundary of top coal has a larger opening range, the rotating angle of lower boundary is relatively small in the normal drawing stage, which is conducive to the development of drawing body and reduces the residual top coal, and the maximum particle velocity and the particles movement angle are both larger. This study lays a foundation for the prediction of recovery ratio, and suggests that the uniform top coal is more manageable and has a larger recovery ratio.

破碎顶煤块的尺寸分布是一个重要因素，影响长壁顶放煤开采面板的顶采率和抽采效率。顶煤块大小（的标准偏差δ_吨）是主要的参数，以反映顶煤的粒度分布中的一个。为了找到的效果δ_吨上放机构，这项研究会模拟实验与9个不同的δ_吨通过使用分立元件软件PFC。该δ_吨被分为两个阶段：均匀分布级（UDS），其δ_吨小于0.1（方案1-5），和非均匀分布级（NDS），其δ_吨大于0.1（方案6–9）。本研究主要研究了两个阶段的采收率，拉拔体形，顶煤边界和颗粒间接触力的变化。结果表明，随着越来越δ _ŧ，面板的回收率在UDS中会先增加然后降低。这是方案3中最大的方案，主要增加了图纸起始端一侧的图纸量。但是，在NDS中，回收率先下降，然后迅速增加，在方案9中是最大的，在方案9中，精加工拉丝端侧的拉丝量相对较高。在UDS中，表层煤的主要尺寸基本为中等，而在NDS中，其尺寸从中到小，然后再到大，并且拉丝体的形状和体积存在明显差异。当顶煤的主要尺寸为中小尺寸时，每个高度的顶煤初始边界的横截面宽度相对较小。相反，当顶煤尺寸较大时，顶煤的初始边界具有较大的开孔范围，在正常拉拔阶段下边界旋转角较小，有利于拉拔体的发展，减少了残余顶煤，最大颗粒速度和颗粒运动角均较大。该研究为预测​​采收率奠定了基础，并表明均匀顶煤更易于管理，采收率更大。