Abstract: The backfill pillar is inevitably disturbed by the blasting vibration in two-step mining. Investigation on its dynamic characteristics has important theoretical significance and engineering value for realizing safe and efficient mining of two-step pillars. Taking tailings cemented backfill as research object， SHPB dynamic uniaxial impact tests with different strain rates were carried out at different axial compression levels. The dynamic and static combined loading strength， deformation characteristics， energy transfer law and failure mode of backfill under one-dimensional dynamic and static combined loading were analyzed. The results showed that: （1） The dynamic strength of the backfill will first increase and then decrease with the the axial load in the case of approximately the same strain rate. The dynamic strength of the backfill sample will increase with the increase of the strain rate in the case of the same axial load， and both of them have a strong correlation relationship. （2） The stress-strain curve of the backfill is mainly divided into three stages: the elastic stage， the yield stage and the failure stage， and the compaction stage is not clearly appeared in impact tests. What’s more， the backfill is not sensitive under low strain rate. （3） The absorption energy slightly increases with the increase of incident energy. The absorption energy per unit volume increases with the increase of strain rate， and the increment of transmission energy decreases with the increase of incident energy. （4） In the case of conventional SHPB tests， the failure mode of the backfill is tensile failure. The failure mode of the backfill is mainly compression-shear failure in the case of the coupled static and dynamic loads.

Key words: Backfill, Coupled static and dynamic loads, Dynamic strength, Deformation feature, Energy transfer law, Failure mode