Seismic Analysis For Open Pit Mines

Open pit mines are of a dramatically different scale and nature to most civil works, so seismic analysis techniques required for open pit mines are also very different to those for civil works. This paper demonstrates two important aspects of the seismic behaviour of open pit mines; site response effects resulting from large scale man-made and natural topographical features, and the effect of earthquake ground motion on seismic stability assessments for steep and high slopes. An understanding of the first aspect is a prerequisite for understanding the second aspect.

The effect of topographical features is generally to amplify ground motion at the crests of pit slopes and ridges, and up through spoil piles. These effects will alter response spectra for infrastructure design. Slip mass scale effects mean that, during an earthquake, the maximum average acceleration within a slip mass is less than the maximum surface acceleration. The combination of these two effects means that the appropriate value of acceleration for use in slope stability calculations is highly dependent on topography, and the size and location of the potential slip mass under consideration.

Seismic analysis techniques for open pit mines are not well established. Two case studies, one of an open pit slope, and one of a large ore spoil pile on a ridge, demonstrate that meaningful insights, based on sound engineering principles and consistent with the literature, can be obtained with the use of appropriate and thorough seismic analysis techniques. It is suggested that dynamic analysis is required to assess seismic behaviour at open pit mines.