Abstract: It is significant to investigate the evolution laws of pore structure during the process of backfill body damage in the surface subsidence zone. In this study, the medical X-Ray CT and small loading devices were employed to conduct real-time uniaxial compression scanning test on the backfill body with a mixture of waste rock and tailings. The multi-component structure models were reconstructed for the backfill body under different stress states. The results show that the backfilling porosity increased, as the stress value grew. When the stress value exceeded 80% of peak stress, the porosity increased sharply. Furthermore, pores were mainly distributed along the X-type conjugate surface. The backfilling porosity increased with the percentage of rock. The backfilling meso-structure evolution can be divided into six stages, including continuous compaction of pores, pore expansion after compaction, continuous expansion of pores, integration and expansion of pore groups, coalescence of adjacent micro-cracks, and pore expansion in heterogeneous areas. When the stress of the backfilling was less than 80% of the peak stress, both the CT number and porosity varied within small ranges. Although no significant penetrating cracks were observed in the backfilling, there were two main states, including the compression and expansion of the primary pores and the initiation and propagation of secondary pores. As the stress exceeded 80% of the peak stress, the CT number reduced drastically, while the porosity increased sharply. Meanwhile, the primary and secondary pore structures gradually connected in the backfilling and then formed penetrating cracks, resulting in the damage of the backfilling body.

Key words: subsidence area, backfill body, X-Ray CT, 3D reconstructed, pore structures