concrete‐filled steel tubular columns, gob‐side entry retaining, supporting system along gob‐side, thick and hard roof stratum, Technology, Science

Abstract The successful retaining of the gob‐side entry under a thick and hard roof stratum is difficult because of the high pressure present and complex construction technology commonly used. To solve this problem, a new type of gob‐side entry supporting system is proposed in this paper. This system is mainly composed of concrete‐filled steel tubular columns (CSTCs), flexible cushion, and gob isolation structures. This new supporting system combines the high‐strength support of CSTCs with the flexible support of cushion bodies and is simple to construct, enabling fast and efficient gob‐side entry retaining under a thick and hard roof stratum. The range of the roof strata controlled by gob‐side support structures is determined for a case study, and a calculation formula for the gob‐side support resistance is established. Through theoretical and experimental research, a reasonable calculation formula for the choice of CSTC is also established. The CSTC structure ultimately selects Φ194 × 8 mm hollow steel tubes and C40 grade concrete for use in a field application, which can provide 4814 kN of supporting force. A simple on‐site construction process is designed for the field application, and the time required for entry retaining per meter is only approximately 40‐45 minutes. This application shows that the new technology controls the deformation of the retained entry very well; the final deformation stabilizes at 412 mm, which meets the engineering requirements.