The strain softening behavior of the rock-encased-backfill (RB) structure decides the stability of the underground backfilling stope during cyclic excavation and blasting. To investigate the cyclic failure behavior of the RB specimen, a series of triaxial cyclic loading experiments were conducted in different volume fractions of rock, confining pressures, and cyclic loading rates. Results show the strain hysteresis curve increases from sparse to dense with the increase of the confining pressure, showing a significant strain-softening characteristic. The elastic strain energy increases linearly and the dissipation energy increases exponentially with the number of cycles. The percentage of shear microcracks during each circle increased quadratically, which was very similar to the trend of dissipation energy. When VF=0.73 and the loading and unloading rate was 400 N/s, the percentage of shear microcracks in RB specimens was higher than that in other cases, especially higher under 9 MPa. This finding indicates that RB specimens are more prone to meso damage and elastic-plastic transformation under a specific condition, and the importance to conduct more studies on the coupling mechanism of the bi-geological-materials structure.
Backfill is one kind of artificial and green material reserved in the underground, which is made with waste tailings after mining excavation. Its mechanical properties are similar to soil and cement, which is far away from that rock mass nearby. After the backfill is consolidated, the field stress will be redistributed in the rock-encased-backfill structure (RB).