An experimental investigation of effects of block shape on the mechanical properties of bimrocks

The shape of rock blocks significantly influences the mechanical properties of bimrocks. To address this gap in research, a new laboratory-based method was proposed to study the effects of block shape, with detailed production techniques for creating rock blocks of various shapes. Uniaxial compression and direct shear test results revealed that block shape markedly affects the stress-strain behavior under uniaxial compression. The elongation index (EI) and flatness index (FI) were found to effectively characterize the influence of block shape on uniaxial compressive strength (UCS), cohesion, and internal friction angle. Interestingly, when the block proportion was 30% versus 60%, the direction of UCS variation on the EI-FI chart reversed, with EI having a greater influence on UCS than FI. Cohesion increased in a counterclockwise direction on the chart, with the minimum cohesion observed in samples with oblate blocks. In contrast, the internal friction angle increased in a clockwise direction, with its minimum value found in samples with blade-shaped blocks. In terms of shear failure, rock cutting along the shear failure surface decreased with decreasing shape factor (SF), with failure more often manifesting as rock bypassing rather than direct cutting.