## 6 Conclusions  
This paper, taking the 91-101 ventilation roadway of Wang-Zhuang Coal Mine as the engineering background, studied the deformation characteristics of the surrounding rock mass of gob-side entry retaining with large-diameter, concrete-filled steel tube roadside support in a fully mechanical top caving working panel. The following conclusions were drawn:  
1. Considering the high strength an adaptability requirements of the roadside supports for roof deformation in gob-side entry retaining in a top caving longwall, large-diameter, sleeve-structured, concrete-filled steel tubes have been proposed as a roadside support body. According to the surrounding rock large-structure characteristics of  
Figure 14: Screenshots taken from video obtained down boreholes at different depths. Figure 15: Realistic view of gob-side entry retaining in 91–101 working longwall. (**a**) CFST construction area; (**b**) T-junction of working longwall; (**c**) retained roadway. gob-side entry retaining in a fully mechanized top caving working panel, a mechanical model was established, and a calculation method for roof subsidence was obtained. 2. A mechanical analysis model of roof rock mass between columns was established to clarify the distribution form of the tensile stress zone, and the Prandtl foundation failure criterion was introduced to determine the critical condition of shear-slip instability in the contact surface between the concrete-filled steel tubes and the roof, which provided a design basis for the stability control and support scheme for the roof between columns. 3. Aiming at the difficulty of surrounding rock control of gob-side entry retaining in a top caving longwall, the process and parameters of gob-side entry retaining with large-diameter, concrete-filled steel tube roadside support were put forward, which effectively guarantee the safe and efficient construction of gob-side entry retaining. 4. Field tests were carried out in the 91-101 ventilation roadway. The roadside support of gob-side entry retaining in the 91-101 ventilation roadway consists of concrete-filled steel tubes with a core sleeve structure; the outer tube is made of a hot-rolled seamless steel pipe with a diameter of 1220 mm and thickness of 10 mm, and the inner tube is made of a waste gas drainage pipe with a diameter of 425 mm and thickness of 3.5 mm, respectively. The deformations of the roof and floor of the roadway were monitored and the results showed that the deformations of the retained roadway roof and floor could be divided into three stages: slow deformation stage, dynamic pressure influence stage, and gradual stability stage. The maximum subsidence of the retained roof reached about 430 mm, and the floor heave of the retained roadway reached 80 mm. The roof probe results showed that the main roof above the roadway was relatively intact, and the basic roadway support system was still in a stable state. The area of the retained roadway section reached 12.9 m\({}^{2}\). In summary, this technology is an important breakthrough in the technical field of non-pillar mining and can be used to reduce the waste of coal pillars and improve the recovery rate of coal resources. Conceptualization, Z.-L.L. and Z.-G.M. ; methodology, Z.-L.L. and O.I.K. ; software, Y.L. ; formal analysis, P.G. ; investigation, Z.-L.L. and P.G. ; writing--original draft preparation, Z.-L.L. ; writing--review and editing, Z.-G.M. and X.-Y.N. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Key Research and Development Projects of China, under Grant Nos. 2019 YEE0118500 and 2019 YFC1904304; Natural Science Foundation of Jiangsu Province, under Grant No. BK20200634; The Natural Science Foundation of the Jiangsu Higher Education Institutions of China, under Grant Nos. 21 KJB130004; National Natural Science Foundation of China, under Grant Nos. 52104107 and 51734009. Not applicable. The data used to support the finding of this study are included within the article.