Application of concrete-filled steel tubular columns in gob-side entry retaining under thick and hard roof stratum: A case study

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 phi 194 x 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.