Millisecond-delay Intervals in Horizontal Layering Bench Blasting Based on the Evaluation Model of the Entropy Weight Method

Millisecond-delay blasting in an open pit is difficult because the development of rock mass horizontal layering and mechanical properties vary widely among rocks. An unreasonable delay time for varied holes and rows often causes poor blasting effects. In this study, the multi-layer rock blasting model in the ANSYS/LS-DYNA software is used to optimize the delay time between holes and rows, improve the blasting effect, and reduce the vibration produced by blasting. The delay time for varied holes and rows is simulated. In line with the evaluation model of the entropy weight method, the maximum effective stress in the three sections is analyzed. The weight coefficient of each index is determined with entropy information theory, and a rock damage model is established. The ratio between the maximum tangential stress of the surrounding rock and the uniaxial compressive strength of the rock and the ratio of the uniaxial compressive strength of the rock to its tensile strength are selected as evaluation indicators. The maximum effective stress in the three sections at different positions between holes and rows is determined and analyzed. The test indicates that the delay time combination of 28 and 100 ms is effective and can avoid the interference of various geological conditions on the blasting effect. In accordance with the evaluation results, this delay time combination is used for field tests. Results demonstrate that the blasting effect of the selected delay time combination is remarkably enhanced, the boulder frequency is low, and the vibration caused by blasting is reduced by 30%. In special geological conditions where the mechanical properties of rocks differ greatly, the evaluation model of the entropy weight method presents crucial advantages in the precise selection of millisecond-delay intervals for horizontal layering bench blasting.