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.