# Study of the Constraint Pillar Test and the Application in Gob-Side Entry Retaining
## 5 Conclusions  
1. By carrying out the bearing capacity test of 1:1 equal-ratio pillars, the conversion error of the bearing capacity caused by the size effect of high-water materials and concrete pillars is overcome. The results show that the bearing capacity of the 0.8 m \(\times\) 3.4 m C30 concrete pillar is 2608 kN, 360 kN, 4980 kN, 7200 kN, 9460 kN, and 11,500 kN, respectively, under the conditions of unconstrained, diamond mesh, polyester-fiber mesh, hooked iron-sheet flat-hoop sleeve, corrugated pipe, and spiral iron pipe constraints, and the bearing capacity of the pillar is 2608 kN, 3360 kN, 4980 kN, 7200 kN, 9460 kN, and 11,500 kN, respectively. It can be seen that the external constraint capacity is enhanced, and the bearing capacity of the corrugated pipe pillar and spiral iron pipe pillar is 3.6 times and 4.4 times that of unconstrained concrete pillar, respectively. 2. This paper analyzes the movement characteristics of the surrounding rock structure in a gob-side entry retaining and the action law of roadway side support and puts forward the requirements for roadway side support. Through the experimental study of the pillars mentioned above, it can be seen that the bellows and spiral iron-pipe/concrete pillars have a strong bearing capacity and certain yield performance, and these two kinds of restrained pillars are feasible as supporting structures beside gob-side entry retaining. 3. The industrial test of gob-side entry retaining in the 50108 working face of Hejiata Coal Mine was carried out, and the supporting scheme of a \(\varphi\) 0.8 m \(\times\) 3.2 m and C30 concrete pillar with corrugated pipe constraint was adopted in the project. Through the test of the retaining roadway and retaining roadway reuse stage, we can see that the surrounding rock of roadway is stable; the deformation is small; the mechani  
Figure 16: Deformation curve of roadway surrounding rock in reuse stage of gob-side entry retaining.  
cal properties of the corrugated-pipe-confined concrete pillar are verified; and the pillar has a large bearing capacity, fast resistance increase speed, high construction efficiency, good stability, certain deformation ability to adapt to roof subsidence, and low comprehensive cost, and it is suitable for the technical requirements of supporting beside gob-side entry retaining roadway in fast advancing working face.  
Conceptualization, J.T., H.K. and D.Z.; data curation, J.T. and G.F.; investigation, J.T. and X.Z.; methodology, H.K., D.Z., G.F. and X.Z.; software, X.Z.; validation, G.F.; writing--original draft, J.T., G.F. and X.Z.; writing--review and editing, J.T., H.K. and D.Z. All authors have read and agreed to the published version of the manuscript.  
Supported by the National Natural Science Foundation of China (52274123); General Project of Science and Technology Innovation Fund of Mining Research Institute of middling coal Technology and Industry Group (KCYJY-2022-MS-01); and key fund project of CCTEG coal mining research institute--research and development of key technologies and equipment for mechanized pillar gob-side entry retaining at high mining height and fast advancing working face in Inner Mongolia and Shaanxi Mining Area.  
Not applicable.  
Data Availability Statement: Data are contained within the article.  
Authors [PERSON] and [PERSON] were employed by the company CCTEG Coal Mining Research Institute. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.