Finite difference modelling of the variation in piezometric head within a rockfill embankment

The subject of flow through rockfill is of increasing interest in Canada. Rockfill drains are presently used by mining companies in order to permit existing creeks to flow through the base of mine waste dumps. There is potential for the use of flow through rockfill dams for mini-hydro schemes because the adoption of a costly concrete spillway may be unnecessary in some cases. An important issue in the design of flow through rockfill structures is the pore pressure distribution and the associated hydraulic gradients, neither of which are associated with Darcy's law. For such determinations the finite difference scheme of Curtis and Lawson, which is based on the partial differential equation presented by Parkin et al., was investigated. However, expressions for edge nodes under this non-Darcy finite difference scheme do no exist. This paper presents the effect on the results of using more direct expressions for the edge nodes. Analytical results are compared with observed piezometric heads in the case of two model flow through rockfill dams. Further, it is shown that through the use of a standard electronic spreadsheet, piezometric heads for non-Darcy flow in porous media and the associated hydraulic gradients can be modelled directly without the need of complex computer programming. Key words: flow through rockfill embankment, piezometric head, finite difference method, non-Darcy flow.