Study on large deformation mechanism and concrete-filled steel tubular support technology for ventilation shaft roadway

The large deformation of deep soft rock roadways and the corresponding support technology are important to the coal mining industry. This study investigated the large deformation mechanism and the concrete-filled steel tubular support technology of a ventilation shaft roadway (VSR) on the basis of a well-documented engineering case. The mechanical parameters of the rock surrounding the VSR were evaluated in accordance with the geological strength index, and the failure modes of the VSR were summarized and analyzed on the basis of geological background and field survey results. The VSR exhibited asymmetrical deformation and the fracture of the 29U-shaped steel support at the side and vault. The deformation, stress, and plastic zone of the VSR without support and with the original support scheme were investigated using the Three-Dimensional Distinct Element Code, and the depth of the plastic zone was verified in accordance with the equivalent radius theory. Dramatic and multiple disturbances, the low strength of the surrounding rock, and the insufficient strength of the support caused the deformation of the VSR. The bottom of the two side walls of the original roadway was prone to inward deformation. Thus, the shape of the original roadway section was optimized by converting it from a straight wall with a semi-circular arch into an inclined wall with a semi-circular arch. A composite concrete-filled steel tubular support scheme is proposed and can be divided into active and passive support. The composite support scheme was verified through numerical simulation and a field application. The monitoring results obtained from the numerical simulation and on-site analysis reveal that the composite support scheme can control the large deformation of the VSR.