A Mechanical Analysis of Support Instability Risk along the Strike of Coalface in Thick Coal Seam with Large Dip Angle: A Case Study

To ensure safe and high-efficiency mining in the coalface with large dip angle (LDA) and large mining height (LMH), it is important to study the support stability of the coalface under the corresponding conditions. This study is based on the #3up509 coalface of the Gaozhuang Coal Mine (GCM) affiliated with the Zaozhuang Mining Area (ZMA), for which the mechanical characteristics of support in the coalface with LDA and LMH are analyzed. On this basis, the mechanical models for support tilting and sliding in the coalface are developed. Then support stability along the strike of the coalface during the normal mining period (NMP) and special mining period (SMP) is analyzed. The results show that the critical support tilting resistance during the NMP is 52.2 kN, and the critical support sliding resistance is 183.75 kN, and for the SMP, the values are 2679 kN and 4425 kN, respectively. The use of a two-leg shield support, known as ZY6600-25.5/55 (its rated working resistance is 6600 kN), is investigated, which is proved reasonable for the coalface. The influencing factors of support stability along the strike include technical parameters of the support, mining geological conditions of the coalface and specific conditions during mining. Technical measures, such as installing interlock set to fasten support and adjustable lifting jack, increasing the setting load of the support, and optimizing the support displacement method, are taken to increase the overall support stability in the coalface. The initial aim for a safe and high-efficiency mining at the #3up509 coalface has been achieved through the aforementioned measures.