| Summary: | To eliminate the massive accumulation of tailings and promote the recycling of mine solid waste to develop green mining, a two-layered cemented paste backfill (CPB) with layering angles of 5°, 10°, 15°, 20° and 25° and complete CPB were prepared to conduct direct shear experiments; thus, the effect of the layering angle on their shear mechanical properties can be investigated. Meanwhile, the particle flow analysis program PFC 2D was used to simulate the micro-crack propagation law and reveal the damage mechanism. The results showed that the layered structure weakens the integrity of CPB and significantly reduces its shear strength, cohesion and internal friction angle. When the layered angle increased from 20° to 25°, the shear strength under normal stress of 100 kPa was decreased by 35.13% and cohesion by 43.43%. As the layered angle increased from 5° to 25°, the internal friction angle decreased first and then increased and reached the minimum when the layered angle was 15°. With the increase in the layered angle, the layered CPB gradually generated tension cracks along the layered surface, and the number of cracks gradually increased. The failure mode of each specimen is mainly a shear crack through the shear surface failure, crack expansion in the middle of shear surface on the upper and lower sides of the spindle-shaped failure and an inverted Z-shaped conjugate shear failure. This research can provide a substantial reference in the design and application of layered CPB in underground mines.
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