Seismic pulse assessment of the changing rock mass conditions induced by mining

Abstract

Cross-hole, high-frequency seismic pulse transmission experiments were performed in three underground metalliferous mine sites and one surface quarry at Mount Isa Mines, Australia. The change in the attenuation of the seismic waves is interpreted as a change in the rock mass conditions at the particular site studied. For the large in situ rock masses at such sites, the pulse rise time method is the only reliable method of assessing seismic wave attenuation. The rise time is a measure of the time taken (usually tens of microseconds) for the seismic pulse onset to reach maximum amplitude; the larger the rise time the greater the attenuation. At each site, a series of high frequency seismic pulse transmission experiments were conducted over the period when conditions in the assessed volume of rock were changing. The alteration in the rock mass conditions was induced by the general mining process (underground sites) or by controlled blasting (surface site). Each seismic pulse experiment involved a low energy source which does not itself contribute to the change in the rock mass conditions being measured. The present results clearly show that for all sites studied, progression of either the production mining or controlled blasting resulted in a significant change in the rock mass condition as assessed by a change in both rise time and travel time of the seismic waves transmitted through the rock mass in question. The results also show that the sensitivity of the pulse rise time to changes in rock mass conditions is at least an order of magnitude greater than the sensitivity of the pulse velocity.