Considerations on the design of flowthrough rockfill drains Garga, Vinod K.; Hansen, D. (David); Townsend, R. D.
Up to the present time the main tool used in the hydraulic design of flowthrough rockfill drains appears to have been Wilkins' (1956) equation. In this Paper the assumptions associated with this equation are discussed in detail. The authors note that piezometers are sometimes installed in rockfill drains to permit mine operators to ensure that a drain is functioning as expected, yet little effort seems to have been expended in verifying whether the observed water levels are in agreement with levels which could be estimated using theoretical considerations. Such modelling can indicate whether the values of parameters assumed in Wilkins' equation were correct and may therefore also indicate whether appreciable clogging of the drain has occurred. This Paper discusses an adaptation of the theory of gradually varied flow for computing the phreatic surface within a rock drain. Wilkins' (1956) equation for non-Darcy flow through porous media utilizes the parameter known as the hydraulic mean radius. In this Paper a rationale is presented for estimating this important parameter. The effect of subzero temperatures on the hydraulic capacity of rockfill drains has been examined for the first time. The possibility of ice build-up within a flowthrough rockfill drain is discussed, including the main modes of heat loss and the role of the viscous dissipation of hydraulic energy.
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