Modeling Rock Blasting
The physical processes occurring in rock blasting span six orders of magnitude in length-scale, time-scale, and pressure. The interactive-physical processes involved are time-dependent, non-linear, difficult to quantify experimentally, and occur in a discontinuous, heterogeneous medium. These factors present a significant challenge to the modeler. Just as blasting is a broad topic, there is no single numerical modeling approach that can address all aspects of rock blasting. Figure 1 shows a vertical logarithmic timescale with with images and time ranges for rock blasting processes.
Figure 1: Rock blasting processes organized along a vertical log scale of time.
This section describes several approaches to modeling rock blasting sub-problems with Itasca Software. From version 9.5 onward, the Jones-Wilkins-Lee (JWL) constitutive model is available to model explosive reaction products, although not all examples in this section use the JWL model directly.
A simple bench blasting design rapid tool is provided to demonstrate widely used empirical models for blast fragmentation and vibration. This tool is available from the i Workspace content selector (choose ). This tool is calibrated for some generic rock types — these are provided to illustrate the general principals and trends. These empirical models should always be calibrated with site-specific data when forward predictions are made.
Moving beyond empirical analysis into a numerical modeling of blasting generally starts with an understanding of the explosive-rock interaction. The FLAC2D 1D explosive-rock interaction example is a starting point. This model takes rock properties, hole diameter, and an explosive and predicts the distribution of the explosive energy. This 1D model is used by subsequent examples as it predicts larger scale vibration magnitudes and burden throw velocities. The explosive rock interaction rapid tool (access via the i Workspace content selector, ) is based on this one-dimensional model.
The axisymmetric 3D (FLAC2D) programmed burn example can be used for detailed study of a single hole detonating at a pre-determined velocity of detonation (VoD) and for study of stemming-blast interaction. Moving to a larger scale, the FLAC3D mine-scale blast vibrations example can be used to explicitly represent blast wave propagation from a multi-hole blast at a mine-scale. Moving to a discrete representation of the rock with PFC3D, the blasting throw example tracks the movement of a rock in a complex blast from the initial position in the bench to the muckpile. This model can be used to optimize muckpiles to avoid rehandling and to track grade during blast movement.
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