## 2 Introduction to Working Face with a Super-Large Mining Height and Difficulty in Roof Control
### Introduction to Difficulty in Roof Control in a Working Face with a Super-Large Mining Height  
The great change in burial depth of the coal seam in the 12,404 fully-mechanized mining face with a super-large mining height and the differences in roof lithology and depth of stratum makes it difficult to predict the mine pressure behavior of the fully-mechanized mining face. Due to the large mining height and the fluctuation of the coal seam, the thickness of bedrock in shallow buried working face varies greatly, and the bedrock ratio also varies widely, so that the mine pressure behavior in the working face shows great differences at different burial depths. Through the engineering analogy method, the mine pressure behavior and roof damage conditions of the 12,403 working face adjacent to the 12,404 fully-mechanized mining face are analyzed to take corresponding countermeasures for the 12,404 fully-mechanized mining face under similar engineering conditions. 1. Mine pressure behavior after the first weighting  
After the first weighting, the periodic weighting conditions of the working face are shown in Table 2 and Figure 1. The weighting step is 17.75 m, the average weighting is 8.9 m, and the non-pressure persistence length is 8.8 m, with little difference. The reason for the long weighting step is that the working face shows continuous weighting, which is manifested as local weighting after weighting, and there is intermittent pressure in the nose, middle, and tail areas. Until the first periodic weighting after first weighting, the working face shows a serious spalling phenomenon. The coal seam is gradually laminated into a concave shape. The spalling depth is large in the 121-125\(\mu\) support area of the tail. The three-level face guard is not connected after it is driven. During the weighting period, the coal seam in the working face shows serious spalling that reaches 3 m at the deepest part. The beam end spacing is large. Generally, there are still two paces after the advanced support is pulled and there is a large cargo capacity when the face guard is taken back. The spalling of 121-124\(\mu\) supports in the tail is the deepest. The three-level face guard has not been connected after it is driven, which is the same during the non-pressure period. Because of the slow advance speed of the working face, burial depth exceeding 240-250 m, large mining height, and large advanced abutment pressure of the working face, the coal wall has been crushed in advance at 3-5 m. With the advance of stoping, the crushed coal wall shows spalling. When the working face advances to 300 m, the advanced pressure increases, the mine pressure behavior of the return air gate road is serious and the upper anchor cable is continuously broken. During the later stoping period, the 121-124# supports show bulk gangue leakage phenomenon (Figure 2). Mine pressure behavior during normal mining period  
The periodic weighting law for burial depth greater than 200 m is as follows: The periodic pressure step is about 16.4 m, showing a \"two large and one small\" law. The large and small periodic weightings alternate, with a maximum pressure of 51-55 MPa (Figure 3). The weightings are strong, generally 30-100\(\#\), as shown in Figure 3. The coal wall spalling at the working face is severe, showing a \"crescent\" shape. Furthermore, due to the prolonged duration of the weightings, the impact range gradually expands in the working face. The subsidence of the support live column is 30-200 mm, and the opening rate of the support safety valve is 5-26%. The periodic weighting law for burial depth less than 200 m is as follows: The periodic weighting step is about 12.58 m. The mine pressure behavior is not obvious compared with that when the burial depth exceeds 180 m. The pressure, generally 35-40 MPa, is not intense and is localized.