Study on Rock Fragmentation under Condition of Delayed Initiation between Holes in an Open-pit Mine

To optimize the initiation delay time of an open-pit mine and enhance blasting efficiency, a three-dimensional bench blasting model is developed using ANSYS/LS-DYNA software. The model consists of 2 blast holes in the front row and 1 blast hole in the back row arranged in a triangular pattern. The bottom initiation was employed, and 5 stress monitoring points were placed within the hole placement area. Simulated tests were conducted to evaluate rock fragmentation under different delay times between rows(42 ms) and between holes(11, 13, 15, 17, 19, 21, and 23 ms), while monitoring their effective stress levels. Additionally, a delayed detonation profile model for the two front row boreholes was established to observe the propagation characteristics of explosion stress waves. The results indicate that when the delay time between rows is set at 42 ms and between holes at 17 ms, it leads to peak values of maximum effective stress at each monitoring point which facilitates overall rock fragmentation. The advantage of time-delay blasting lies in its ability to enhance rock damage by utilizing the pre-blast hole as a foundation, while the front-row hole acts on the post-blast hole through pre-detonation effects, creating a new free surface. Through field testing and demonstration, we analyzed the distribution of rock fragmentation in blasting pile photos using split-desktop software. The findings indicate that with an inter-row delay time of 42 ms and an inter-hole delay time of 17 ms, approximately 77.24% of rocks are below 20 cm in size, while only a negligible proportion(0.31%) exceeds 50 cm. Overall, the crushing effect is satisfactory and meets both production and operational requirements for open-pit mining operations.