Effect of horizontal drain size on the stability of an embankment dam in steady and transient seepage conditions

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Application of a horizontal drain in an embankment dam has been a prevalent method to lower the phreatic line and dissipate the excessive pore water pressure. The efficiency of this type of drain is often attributed to its length, while the effect of thickness is ignored. In this research, a series of tests were accomplished and different drain sizes including different thicknesses and lengths were applied to a physical model of an embankment dam. During the tests, the pore pressures were measured both in the steady and transient conditions using a number of peizometers and pressure sensors. In steady state, the increased thickness prevented the occurrence of piping and in transient state guaranteed the stability of the upstream slope. However, the thickest drain used in this research showed different efficiencies depending upon the applied length. For the maximum effective length derived from the equations, the increase in thickness could efficiently prevent the undesirable consequences of excessive pore water pressure.


Embankment dam, horizontal drain, pore water pressure, factor of safety, transient seepage

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