Analysis of Water Flow under Non-Saturated Conditions in Waste Piles

Symposium Rouyn-Noranda 2002
Omar Fala, Vincent Martin, Bruno Bussière, Robert Chapuis,
Abstract Waste piles containing reactive sulphide minerals constitute a favourable environment for the production of acid mine drainage (AMD). Within the waste piles, the physical, geochemical and biological processes leading to AMD are numerous and complex. Water distribution and movement in the piles are some of the critical aspects affecting AMD generation. Through digital modelling, we can understand, and eventually control, the movement of water (and thus reduce AMD production) in the waste piles during mining and at mine closure.

Several digital simulations of non-saturated flow in the waste piles were carried out. In these simulations, we considered various types of materials, atmospheric conditions and geometric configurations. The software used is based on finite-element analyses to solve the non-saturated flow equations. The simulations carried out show that we can control the movement of water by introducing layers of fine material within the coarse material of the waste piles. Horizontal layers are however not appropriate since they can, in certain cases, favour the creation of humid zones that could amplify the AMD effects. Layers of material with a slight slope towards the exterior alleviate this problem. Inclined layers favour drainage of the waste piles towards the periphery.

In this presentation, we will describe the physical phenomena that control flow in the waste piles, and we will present several case histories that show the effect of the factors influencing the movement of water. Implications for AMD control are also discussed.
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