Abstract

The N00 mining method, as a novel coal mining technology, differs greatly in both the mining process and key technologies from traditional coal mining methods. To maintain entry stability under such new mining conditions, the stress and deformation process of the rocks surrounding the entry were analyzed based on the Mohr–Coulomb theory in this paper. The following results are concluded: the surrounding rocks of the entry formed with the N00 mining method usually experience eight different stress states. Consequently, the entry deformation also goes through eight development stages. In these eight stages, under the primary stress state (stage I), the entry deformation is negligible. After coal seam excavation is started (stage II), the surrounding rocks of the entry will immediately show a trend of large deformation. Next, after roof support (stage III) and roof cutting (stage IV) are implemented, the entry deformation velocity will decline obviously. However, the entry will continue to deform for a long time when the roof rock stratum at the back of the working face begins to move (stage V). The entry deformation tends to be stable until the roof stratum stops moving (stage VI). When the adjacent working face is mined (stage VII), the entry at a certain distance in front of the working face will once again demonstrate prominent deformation. After the adjacent working face is extracted, the entry will be in the goaf (stage VIII) and become damaged. Furthermore, numerical modeling and engineering measurements are adopted to analyze the deformation and stress evolution process of the surrounding rock. The same results as provided by the theoretical analysis are obtained. The above research results show that there are three potential critical stages for the entry formed by the N00 mining method. To ensure entry stability, the clarification of these three critical stages, timely support and roof cutting are vital measures that can be taken. At the same time, roof temporary support and advance support are essential in the process of roof movement and during the mining of the adjacent working faces.

Article Highlights

1. 1.

   Mohr circle models for stress evolution of N00 mining method were established.

2. 2.

   Stress evolution characteristics were revealed and divided into 8 states.

3. 3.

   Potential dangerous and control measures during N00 mining process are pointed out.

中文翻译：

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N00采留留空沿空巷应力变形演化特征

摘要

N00采煤法作为一种新型采煤技术，在开采工艺和关键技术上都与传统采煤方式有很大不同。为了在这种新的开采条件下保持入口稳定性，本文基于Mohr-Coulomb理论分析了入口周围岩石的应力和变形过程。得出以下结论：采用N00开采方法形成的入口围岩通常经历8种不同的应力状态。因此，入口变形也经历了八个发展阶段。在这八个阶段中，在初级应力状态（阶段 I）下，入口变形可以忽略不计。煤层开挖后（二期），入口围岩立即呈现大变形趋势。下一个，实施顶板支护（Ⅲ期）和顶板切割（Ⅳ期）后，入口变形速度明显下降。但是，当工作面背面顶板岩层开始移动时（阶段V），入口将继续变形很长时间。入口变形趋于稳定，直到顶板停止移动（阶段 VI）。当相邻工作面开采时（第七阶段），工作面前方一定距离的入口将再次表现出明显的变形。相邻工作面开采后，入口将进入采空区（VIII 期）并损坏。此外，通过数值模拟和工程测量，分析了围岩的变形和应力演化过程。获得了与理论分析所提供的结果相同的结果。上述研究结果表明，N00开采法形成的入口存在三个潜在的临界阶段。为了保证入口的稳定性，明确这三个关键阶段，及时支护和切顶是可以采取的重要措施。同时，顶板临时支护和超前支护在顶板移动过程中和相邻工作面开采过程中必不可少。

文章亮点

1. 1.

   建立了N00开采法应力演化的莫尔圆模型。

2. 2.

   应力演化特征被揭示并分为8种状态。

3. 3.

   指出了N00开采过程中的潜在危险和控制措施。