Approximate models of blast vibration in non-isotropic rock masses

It is well known that variations in the local geology of rock masses will influence the transmission of blast vibration. For example, the vibration within a jointed rock mass will depend upon the number and spacing of joints as well as the joint orientations. As another example, the vibration within any rock that exhibits a seismic velocity anisotropy will depend upon the degree of velocity variation in given directions. The present work describes approximate models for the transmission of blast vibration in such rock masses. These models consist of two components. The first component is a Dynamic Finite Element Model (DFEM) to describe the radiation of a single blasthole in the particular geology of interest. The second component is a Monte Carlo waveform superposition model (MCWSM) to account for a delayed sequence of such blastholes within a rock mass. This combined DFEM-MCWSM approach predicts that the vibration depends upon the direction of blast hole initiation with respect to the strike direction of geological features. If the angle between these two directions is chosen carefully, then the vibration can be reduced. This allows for the selection of appropriate delay sequences to minimise blast vibrations within the local geology, and is thus clearly relevant to wall control blasting.