## 1 Introduction
This puts forward higher requirements for the roadside support body: a faster rate of resistance increase, higher terminal support strength, better post-peak load-bearing characteristics, and deformation adaptability. Based on this, [PERSON], [PERSON], etc. [16; 17; 18], proposed using a concrete- or high-water-material-filled flexible formwork as the roadside support body in gob-side entry retaining and applied this technology in the Zhang-Cun Coal Mine and Gao-He Coal Mine of the Lu'an Chemical Group successfully. Although the concrete- or high-water-material-filled flexible formwork wall has a great bearing capacity and deformation applicability, this kind of roadside support body has high requirements for its coal mine transportation capacity, which limits the use of this technology. [PERSON], [PERSON], et al. [19; 20] put forward using concrete-filled steel tubes combined with gangue bags as the roadside support in gob-side entry retaining and applied this in the Lu'xi coal area successfully. Concrete-filled steel tubes have high support strength and require less transportation, but the use of gangue bags has greatly increased labor intensity [21]. In this case, this study put forward the technology of gob-side entry retaining in a fully mechanized top-coal exiting longwall with a large-diameter, core sleeve structure, concrete-filled steel tube as the roadside supports. Concrete-filled steel tubular columns with sleeve structures have several advantages: higher support resistance, better post-peak bearing characteristics, a larger cross-sectional of the retained roadway, lower transportation capacity requirements, lower labor intensity, a simpler process flow, etc. Since this technology eliminates the auxiliary support, gangue bags, wood pillars, etc., between the concrete-filled steel tubes, the stability control of the roof between the concrete-filled steel tubes becomes a critical issue. Therefore, further research and discussion are needed on the problems of the stress distribution characteristics of roofs between columns and the optimization of roadway side support parameters. Taking 91-101 working faces (the thickness of top coal is about 2.95 m, and the top coal is induced to cave through a tail boom device behind the hydraulic support in a working face) in the Wang-Zhuang Coal Mine of Shanxi Lu'an Chemical Group as the background, the focus was on the problem of the high pressure of the surrounding rock and the poor stability of the roadside support in the gob-side entry retaining in a fully mechanized top-coal caving longwall; a mechanical analysis model of a roof structure of gob-side entry retaining in a fully mechanized top-coal caving longwall was built, the calculation formula of the roadside support parameters was derived, and the evolution analysis model of the conical tensile stress zone between the columns was established. Combined with the numerical simulation, the stress evolution law and deformation characteristics of the surrounding rock of the gob-side retained roadway with a large-diameter, sleeve structure, concrete-filled steel tube roadside support in a fully mechanized top-coal working face were studied [22; 23]. Meanwhile, a safe and efficient construction process of gob-side entry retaining with a large-diameter, concrete-filled steel tube roadside support in fully mechanized caving face is proposed, with the key point of advance roadway roof reinforcement, large diameter core sleeve structure concrete filled steel tube discontinuous roadside support, cross bracing I-steel roof protection between columns and rapid prototyping roof contacting. Filed practice was carried out and the actual length of the gob-side entry retained roadway reached 2500 m, field data monitoring showed that the deformation of roadway roof and floor reached stability after about 100-120 m lagging behind the working longwall. This study can provide a reference for similar condition coal mines.