## 1 Introduction  
To reduce the amount of roadway excavation and improve the resource recovery rate [1] in recent decades, a pillarless longwall mining method called gob-side entry retaining (GER) has been studied and applied under different geological conditions in China [2]. Gob-side entry retaining technology not only reduces the waste of coal resources, but also makes the ventilation form with a \"Y\" layout, which can eliminate the risk of gas accumulation in the upper T-junction of the longwall [3]. At present, some types of gob-side entry retaining technology have been successfully applied in coal mines with a shallow buried depth, thin coal seams, and simple roof structures [4, 5]. With the average mining depth of coal seams increasing, geological conditions are more complex, causing too many difficulties in the application of gob-side entry retaining under the condition of a large buried depth coal seam [6]. In this case, [PERSON], etc. [7, 8, 9], proposed the means of gob-side entry retaining by using directional blasting to cut off the overhanging roof on the side of the gob and set large deformation constant resistance anchor cables in the roof of the roadway to reinforce the roof, make the severed, overhanging roof fall down, and form a roadway subsequently. This technology opens up new ideas and directions for pillarless mining in large-depth coal seams and achieves a good application effect in Yu-Lin mining areas in northern Shaanxi province [10]. The application effect of'self-forming roadway by roof cutting' is good in thin coal seams and medium-thick coal seams with a thickness of less than 4.5 m, and most studies are also mainly focused on the application of'self-forming roadway by roof cutting' in the conditions of thin coal seams and medium-thick coal seams [11]. However, for coal seam thicknesses greater than 4.5 m, due to the complex spatial relationship between the hydraulic supports in front of the working longwall, the top-coal mass, and the overlying rock strata, there is a great risk of hydraulic supports being crushed during the process of top-coal falling after the pre-splitting blasting cuts off the main roof [12]. Moreover, the problems of residual coal and gas accumulation pose a great safety risk through use of delayed blasting cutting roof. Therefore, it is difficult to realize a'self-forming roadway by roof cutting' under the condition of top-coal exiting; the applicability of the'self-forming roadway by roof cutting' is not good in thick coal seams with top-coal exiting; thus, gob-side entry retaining with side support still is an effective safety method in thick coal seams of fully mechanized working longwall [13]. Past research has shown that the deformation of the immediate roof, side wall, and immediate floor of the gob-side retained roadway are closely related [14]. The deformation of the immediate roof directly above the roadside support body determines the rotation of the main roof; excessive rotary deformation of the roof directly above the roadside support body will cause a series of chain reactions, such as failure and bulge of the solid coal wall, separation and breakage of the roof, the anchor cable sheared off, etc. Moreover, since the conversion of unloading-supporting determines a certain given deformation of the roof, strictly controlling the unmanageable deformation of the roof will cause a sharp increase in costs, instability of roadside support, and roof punching failure [15]. Thus, the key to surrounding rock control of gob-side entry retaining in the top caving longwall is to ensure that the deformation of the roof above the side support is within a reasonable range. This requires that the roadside support body not only has great support resistance in the early stage to ensure that the contact surfaces of the top-coal, immediate roof, and main roof are not separate, but also have the good post-peak bearing characteristic of 'cracked but not broken' and ensures the support body will not become invalid suddenly under a load of the overburden rock mass.