## 2 Introduction to Working Face with a Super-Large Mining Height and Difficulty in Roof Control  
### Overview of Working Face  
Taking the 12,404 fully-mechanized mining face with a super-large mining height of 8.8 m in the Shendong Shangwan Coal Mine as an example, Shangwan Coal mine is located in Wulan Mulun Town, Yijin Horo Banner, Ordos City, Inner Mongolia Autonomous Region. The width of the 12,404 fully-mechanized mining face is 280.6 m, the coal seam inclination is 1-5\({}^{\circ}\), the advance length is 5309 m, and the designed mining height is 8.6 m; the ground elevation of this fully-mechanized mining face is 1154-1318 m, and the floor elevation of the coal seam is 1044.61-1073.81 m. There is a lime ditch diagonally crossing the connecting surface of working faces 10-21. The thickness of the overlying bedrock in the ditch is 95-124 m. This ditch is a seasonal ditch flow and a large flood discharge channel in this area, with a normal flow rate of 60 m\({}^{3}\)/h. In the mining area of the 12,404 working face, there are 18 ponds, with a water accumulation of about 61,500 m\({}^{3}\) and good water yield. The characteristics of the roof and floor in the 12,404 fully-mechanized coal face are shown in Table 1. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Roof and Floor** & **Rock Name** & **Thickness (m)** & **Lithological Characteristics** \\ \hline Main roof & Fine-grained sandstone & 5.68–20.34 16.89 & Grey-white, gray-black stratification plane, fine-grained sandy texture, argillaceous cement, with horizontal bedding, wavy bedding, and cross-bedding \\ Immediate roof & Sandy mudstone & 0.8–13.49 7.48 & Grey-white, sandy peilite texture, ragged, flat, dense and hard fracture, containing pyrite nodules, with cross-bedding and wavy bedding \\ False roof & Carbon mudstone & 0.3–0.10 0.2 & Black, argillaceous cement, massive structure \\ Immediate floor & Mudstone & 1.15–5.75 2.19 & Black gray, peilite texture, flat and dense fracture, massive structure, containing phytolith \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Characteristics of roof and floor in 12,404 fully-mechanized coal face. The main roof is fine-grained sandstone, with a natural compressive strength of about 17.62-23.68 MPa and a Protodyakonov coefficient of about 2.16-2.37. The immediate roof is sandy mudstone, with a natural compressive strength of about 19.58-40.16 MPa and a Protodyakonov coefficient of about 2.18-3.74. The false roof is carbon mudstone, with a natural compressive strength of about 23.26-29.00 MPa and a Protodyakonov coefficient of about 2.33-2.9. The immediate floor is mudstone, with a natural compressive strength of about 19.23-21.83 MPa and a Protodyakonov coefficient of about 2.18. The positive side of the rubber transport roadway for the 12,404 fully-mechanized mining face with a super-large mining height is equipped with \(\Phi\) 27 \(\times\) 2400 mm fiberglass anchor rods at a row spacing of 1 m, 5 rods per row at a spacing of 1-1.1 m. The positive side of the air-return roadway is equipped with \(\Phi\) 32 \(\times\) 2400 mm fiberglass anchor rods at a row spacing of 1 m, 5 rods per row at a spacing of 1-1.1 m.  
A total of 120 supports are arranged in the 12,404 fully-mechanized mining face with a super-large mining height, including 5 face-end supports (3 in the nose and 2 in the tail), and 4 transition supports (2 in the nose and 2 in the tail). The setting load of the support is 25.2 MPa. The supports are closely arranged, and the top beam between the supports cannot exceed 100 mm. The support spacing is controlled by the side pushing jacks during the moving process. When the pressure is large, coal cutting measures are taken after the roof is protected by pre-support. Three cylinders that have a rated resistance of 9000 kN are used for advanced supporting of the gate road for the rubber conveyor belt.