## 1 Introduction
Classification basis: according to the combination of direct roof lithology (homogeneous/non-homogeneous) and the number of key layers (single/double), four types of roof structures are classified. 3. Derivation of mechanical equations of support resistance: the static equations of equilibrium are set up by taking the roof support-coal wall system as the object, and the impacts of the depth of sheet-help on the direct roof load and the additional load of the step rock beams are emphasized. 4. Parameter calibration: based on the measured data in the mining area of western China (e.g., the working face of Bulianta 32206), we determine the empirical parameters, such as the rock layer capacity, the crushing expansion coefficient, etc., and validate the range of values by quoting the industry standard (MT/T 592-2011). 5. Equation integration: we combine the bracket efficiency with the load transfer factor and derive the generalized equation of the four types of structural models for support resistance. Top Plate Structure Under Coal Wall Sheet Ganging in Large Height Working Faces of Shallow Buried Coal Seams  
The main reason for the strong pressure in the shallow coal seam is related to the composition of its key strata. The roof bedrock of the ordinary slope is thick, and there are multiple sets of key strata. The lower key strata closest to the stop are protected by the upper multiple sets of key strata, and they are in the decompression zone, so the stope pressure is not large. However, there are only one to two groups of key strata in the shallow coal seam, and the upper part of the key strata is a weak load layer until the surface. The roof's structure is not easy to stabilize, resulting in rapid weighting. Therefore, according to the characteristics of key strata, shallow coal seams can be divided into two categories: typical shallow coal seams and near-shallow coal seams [22]. (1) Typical shallow coal seam. For shallow coal seams with thin bedrock and a thick, loose load layer, the roof breaking movement is manifested in the form of overall cutting, which is prone to roof step subsidence. This kind of shallow buried coal seam with a thick loose layer and thin bedrock is called a typical shallow buried coal seam, which can be summarized as a coal seam with a shallow buried depth and a single key layer structure of the main roof. (2) Near-shallow coal seam. For the shallow coal seam with relatively thick bedrock and a relatively thin loose load layer, the law of mine pressure behavior is between the ordinary working face and the shallow coal seam working face. The roof structure presents two groups of key layers, and there is a step sinking phenomenon, which can be called a near-shallow coal seam. Based on the roof structure model of single and double key strata [23], this paper refers to the direct roof structure model [24] to establish the calculation model of key strata-direct roof combined support resistance in shallow coal seams. Analysis of Direct Roof Structure Under Coal Wall Sheet Ganging in Large Height Working Faces of Shallow Buried Coal Seams  
Field observation, simulation experiments, and theoretical derivation have consistently pointed out that [25] with the increase of mining height, the balanced structural rock strata in the large mining height area will move up, and the hinged balanced structure can be formed under the condition of conventional mining height, while in the case of large mining height, fractures will occur, and then collapse to the goat. In this study, the strata that cannot form a balanced structure are defined as \"immediate roof\". It can be seen that the thickness of the immediate roof in a large mining height stope is usually greater than that of conventional mining heights. In general, the immediate roof thickness of large mining heights is 2.0 to 4.0 times its mining height [26], which indicates that it includes not only the rock strata that easily fall with mining but also the rock strata that are considered the basic roof in conventional mining heights.