Monitoring of tailings dams with geophysical methods

Several dam failure accidents have occurred during the last years and mine tailings dam failures are occurring at relatively high rates. Studies of past earth dam failures show embankment dam problems and failures are often related to internal erosion in one way or another. Geophysical methods have the potential of detecting internal erosion processes and anomalous seepage at an early stage of their development. The methods have been tested to monitor and investigate earth dams; however the methods have not been used very much in mine tailings dam. The present study has been conducted to test the applicability of geophysical methods, mainly electrical resistivity and self-potential (SP), for detecting anomalous seepage through mine tailing dams and monitoring the physical condition of the dam. Field measurements of resistivity and self-potential have been performed in the Kiruna, Aitik and Kristineberg tailings dams to look for streaming potentials, inhomogeneities and time variations of electrical properties and self-potentials. SP and resistivity measurements have also been carried out with fixed electrodes in the Kiruna and Kristineberg dam at a roughly monthly interval during one year starting in November 2003 and ending in October 2004. Laboratory measurements of resistivity have been carried out on different soil samples from the tailings dams to look for eventual changes in electrical properties with change in grain size and water content. The electric resistivity survey in the Kristineberg provides a good image of the subsurface resistivity distribution associated with filling materials and water table in the dam. The results of the electrical resistivity survey from 2004 on the Kristineberg tailings dam are fairly similar to those obtained from in 2003. The SP distribution in the dam also reveals that there are no significant changes in SP values from 2003 to 2004. The resistivity from the fixed electrodes indicates a seasonal variation in the apparent resistivity representing the freezing and thawing effect within in the dam. The SP measurements from the fixed electrode at the Kristineberg dam, shows fairly stable values during summer and more unstable during the winter probably due to change in contact resistance. The result from the 2002 SP measurements in the Kiruna dam reveals a general pattern of positive SP values at the downstream side, which is in agreement with the expected result of streaming potentials developed over the dam core. The