## 1 Introduction  
In recent years, the intensity of coal mining has been increasing, and a single mining area may form one or even multiple isolated working faces. At the same time, in order to reduce resource waste, coal pillar-free mining technology and the layout of ultra-long working faces have been widely applied [1,2]. Therefore, the number of ultra-long fully mechanized mining island working faces without coal pillars is increasing. The main problem with the ultra-long fully mechanized mining island working face without coal pillars is that the surrounding rock deformation and damage of the roadway in the advanced area of the reused goat retaining roadway working face are severe [3, 4, 5, 6], especially the bottom bulge can reach 1-2 m [7,8]. The reason for the above on-site problems is due to the unreasonable surrounding rock control technology under these conditions. Therefore, it is of great significance to study the surrounding rock control technology for retaining roadway in ultra-long fully mechanized mining island working face without coal pillars. [PERSON], [PERSON], and others [9,10] used FLAC3D software to study the distribution law of advance support pressure and the distribution characteristics of coal pillar support pressure in the advanced area of the ultra-long fully mechanized caving island working face and the movement of overlying strata. They believed that the pressure increased within the influence range of the coal pillar support pressure peak to the front of the coal wall. [PERSON], [PERSON], and others [11] studied the characteristics of the collapse structure of the overlying rock and the corresponding mining pressure manifestation law of the deep ultra-long island working face in order to solve the problem of controlling the rock strata of the working face after increasing the mining depth and working face length. They believed that as the length of the working face increased, the middle roof of the working face did not break at once; instead, it broke in different areas in the direction of inclination, and there were multiple pressure peaks in the working face. Academicians [PERSON] and [PERSON] [12] studied the breaking characteristics and pressure situation of the overlying key layer, the activity law of the upper coal (rock) layer, and the impact of the main key layer breaking on the mining pressure manifestation of the 4326 fully mechanized top coal caving ultra-long working face in Wangzhuang Mine through similar simulation and on-site observation. They believed that as the length of the fully mechanized top coal caving working face increases, the breaking block size of the overlying key layer in the mining face will correspondingly decrease. Therefore, the mining pressure in the mining face will be uniform, which is conducive to the top coal breaking and releasing, but the main key layer pressure phenomenon will occur. In terms of the technology of retaining roadway along flexible formwork concrete walls, [PERSON] [13] analyzed the stress of the surrounding rock of shallow buried coal seam retaining roadway along the roadway and conducted on-site measurements of the retaining roadway along the roadway. It was found that the support strength of the flexible formwork concrete wall retaining roadway along the working face meets the requirements, the top and bottom plate movement is 8% of the roadway height, and there is almost no deformation on both sides. The lag peak pressure is 60 m-90 m away from the working face, and the retaining roadway is stable. [PERSON] [14] analyzed the stress evolution law and plastic zone distribution of the surrounding rock of the roadway during the process of retaining the roadway in response to the problems of large deformation and slow construction speed of the flexible formwork wall along the roadway. He developed a scientific technique for resetting and moving the retaining bracket and temporary support along the roadway, which can enhance the support effect of the roadway along the roadway.