A search for distribution of competent layers under tailings by Multi-channel Analysis of Surface Wave (MASW) ? A case history

Abstract

The Multi-channel Analysis of Surface Wave (MASW) method is a shallow seismic method which may complement the traditional seismic refraction method used in engineering applications. Introducing this newly-developed method, this paper presents a case history of an MASW survey in a tailings dam, where the original topography has been covered with tailings (red mud) from an aluminium refinery over the years. An eight-line 3.6 kilometre MASW survey was carried out in the tailings dam of Queensland Alumina Limited in Boyne Island near Gladstone, Queensland to estimate the depth of the competent layer for construction of a new tailings dam wall. The field procedure used was similar to the off-end shooting method used for seismic reflection surveys. This was further simplified by the use of a purpose-built 24-channel land streamer. The seismic source was a weight dropping system mounted on a vehicle, which drops a 50kg steel weight from a height of 0.8 metres. The recording system used was a Seistronix RAS-24 seismograph. The data were analysed and inverted using the SurfSeis software by Kansas Geological Survey. The depths of the original surface and underlying clay are profiled in terms of their S-wave velocities. The result shows the effectiveness of the MASW method even where velocity reversals are present.