In the reuse stage of a gob-side entry retaining, failure of the structure and stability of the main roof have a significant effect on the safety of the advanced support and ventilation space at the working face. In this study, field investigation, theoretical analysis, and industrial experimentation were performed to analyse the fracture characteristics and formation process of the gob-side entry retaining roof during the reuse period. A dynamic-equilibrium mechanical model of the main roof structure is presented and the formation mechanisms of different types of short cantilever rock beam structures are clarified. The following major conclusions are drawn: (1) Three types of short cantilever rock beam structures occur in the main roof of a gob-side entry retaining during the reuse period, namely, the “short cantilever-articulated rock beam” structure, “short cantilever step rock beam (type I)” structure, and “short cantilever step rock beam (type II)” structure. (2) The stability criterion for these three short cantilever rock beam structures was also determined; that is, when the sliding instability coefficient K ≥ 1, the short cantilever-articulated rock beam structure will form, and when the sliding instability coefficient K < 1, the short cantilever step rock beam (type I or II) will form. (3) The governing law for the thicknesses of the main roof, immediate roof, and coal seam of the short cantilever rock beam structure was clarified; namely, the K-value gradually increases with increases in the thickness of the coal seam, drops sharply and then decreases gradually with increases in the thickness of the main roof, and decreases slowly with increases in the thickness of the immediate roof. The research results were validated at the gob-side entry retaining project in the Huainan mining area and have theoretical significance and reference value for roadway support projects with similar conditions.

中文翻译：

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再利用期短悬臂岩梁结构及采空区留存顶板机理

在采空区入口保持的再利用阶段，结构的破坏和主顶板的稳定性对工作面高级支撑和通风空间的安全性具有重大影响。在这项研究中，进行了现场调查，理论分析和工业实验，以分析回采期间采空区侧进水挡土墙的断裂特征和形成过程。提出了主屋盖结构的动力平衡力学模型，阐明了不同类型的短臂悬臂梁结构的形成机理。得出以下主要结论：（1）在再利用期间，采空区入口留存的主顶出现三种类型的短悬臂岩梁结构，即：“短悬臂铰接式岩石梁”结构，“短悬臂阶梯式岩石梁（I型）”结构和“短悬臂阶梯式岩石梁（II型）”结构。（2）确定了这三种短悬臂岩梁结构的稳定性准则；也就是说，当滑动不稳定性系数K≥1时 ，将形成短悬臂铰接的梁结构，而当滑动不稳定性系数K  <  1时，将形成短悬臂阶梯式岩石梁（类型I或II）。（3）明确了短悬臂梁结构主顶，直顶，煤层厚度的控制规律；即，K-煤层厚度随煤层厚度的增加而逐渐增加，急剧下降，然后随主煤层厚度的增加而逐渐减小，而随近煤层厚度的增加而缓慢减小。该研究结果在淮南矿区采空区留巷工程中得到了验证，对于条件相似的巷道支护工程具有理论意义和参考价值。