Influence of Weak Interlayer Angle on Slope Pre-split Blasting

Weak interlayers can easily lead to problems such as over-excavation, under-excavation and low semi-porosity in slope pre-split blasting, and it is critical to clarify the influence of its angle on the blasting effect to optimize the blasting parameters. In this paper, the numerical simulation method is employed to systematically investigate the mechanism of multiple weak interlayer angles on the pre-split blasting effect, utilizing the ANSYS/LS-DYNA finite element program as the technical platform. Based on the physical properties of rock, joints, air and explosives, four types of material models were selected:the HJC concrete model simulated the rock, the PK bilinear follow-up hardening model represented the joints (weak interlayer), the ALE model represented the air, and the HEB model described the explosives. The non-reflection boundary condition is introduced to reduce the reflection interference of boundary stress waves, and the study is parameterized for quantitative analysis. A three-dimensional numerical model was constructed, including eight blast holes. The height of the bottom and upper benches was 200 cm and 1200 cm, respectively, and the slope angle was 80. When the grid is divided, the blast hole and the surrounding area are encrypted, and the global grid is 50cm long to balance the calculation efficiency and accuracy. The simulated conditions include a complete slope and some weak interlayer slopes with angles of 45° and 90° to the blast holes. The stress changes are tracked through the monitoring points (located at the middle and bottom of the model), and the stress wave propagation, pre-split formation process, and overbreak characteristics are analyzed. The final results show that the weak interlayer exacerbates stress concentration, and the overbreak is more severe at a 45° angle. Additionally, the pre-split flatness is poor, and the semi-porosity is low. At an angle of 90°, the degree of overbreak is relatively light. The barrier and energy absorption effects of the weak interlayer decrease with an increase in the angle and increase with an increase in the number.