An Approach to Determine the Hoek–Brown Rock Mass Disturbance Factor in Open-Pit Mining Through Near-Field Peak Particle Velocity

The Hoek–Brown disturbance factor (D) is a critical parameter for quantifying the degree of rock mass degradation induced by blasting or excavation in open-pit mining. However, accurately defining D in open pit coal-mine slopes is particularly challenging due to the toe crushing of weak coal seams, joint dilation or opening, bedding-parallel shearing, and tensile fracturing of intact blocks. Such interacting processes complicate the assessment of overall disturbance, yet a reliable evaluation of D is essential for improving the accuracy of slope stability analyses. In this work, a framework for determining the post-blast D factor extent was developed by integrating controlled blasting experimental data with damage analysis. Peak particle velocity (PPV) and post-blast crack density data from NIOSH tests were analysed to establish quantitative correlations, which were then used to develop a generalized model for assigning post-blast D values from PPV. This model enabled the conversion of field-measurable parameters into spatially distributed damage indices, thereby improving the practicality and repeatability of D determination. Based on these findings, a set of guidelines has also been proposed for defining D in field-scale high wall assessments in surface coal mining environments, and the Heelan-Blair vibration model is used to demonstrate the practical application of the proposed approach. Overall, the developed approach provides a convenient, robust, and reliable method for estimating blast-induced rock mass damage and determining appropriate D values, offering valuable support for blasting design optimization, post-blast damage evaluation, and subsequent slope stability analysis.