Bearing mechanism and stability monitoring of cemented gangue-fly ash backfill column with stirrups in partial backfill engineering

To increase the bearing capacity of an unconfined backfill column (UBC) in partial backfill engineering, stirrups reinforcement is used. To study the bearing mechanism of UBC with stirrups, the stress-strain curves of two UBCs (800 x 800 x 1600 mm(3)) were obtained using a uniaxial compression test. The columns were made of cemented gangue-fly ash backfill material (CGFBM), and only one column has stirrups. The failure characteristics of the CGFBM columns were monitored by photography and ultrasonic testing (UT) techniques. The internal stress and deformations of the CGFBM columns were monitored by the embedded sensors at different positions (50 mm, 200 mm and 400 mm from the surface). It was found that stirrups can prevent the sudden instability of a CGFBM column under uniaxial compression load. The existence of the rectangular efficient bearing core improves the compression bearing capacity and ductility of the CGFBM column with stirrups. The stability of the UBC in the partial backfill engineering can be monitored based on the change of internal stress and deformations. The experimental findings could be used to guide the design, stability monitoring and control of UBC in partial backfill mining engineering.