Seepage Flow along Outlet Conduit in Reservoir Embankment

Restraint of piping failure with flexible conduit

Abstract

An outlet conduit is installed underneath a reservoir embankment. The overage reservoir embankment has often deteriorated contact pressure between the outlet conduit and the fill, and involved latent flow path. When a heavy rain or an earthquake damages embankment by piping failure, it is inferred that these weak points around outlet conduit is a main factor.
In this paper, model tests and numerical analyses were conducted, focusing a seepage condition and a making process of flow path around outlet conduit, to confirm the effective outlet conduit structure to restrain from piping.
Results are summarized as follows:(1) Numerical analyses agree well with the experiments when a coefficient of permeability around outlet conduit area is assigned higher than the other area.(2) Cut-off collar takes effect to raise a critical hydraulic gradient around a conduit and it is inferred that the movement of soil particles along a conduit rather than the length of seepage path influences piping behavior.(3) The outlet conduit having flexible joints fits to the gap caused by making flow path or local settlement of ground, therefore it is more resistant to piping failure than the rigid conduit without flexible joints.