The high pore pressures within embankment dams: an unsaturated soil approach

Abstract

Pore pressures substantially higher than expected are frequently measured within the cores of large dams. Typical observations are presented, and various hypotheses proposed to explain this phenomenon are summarized and briefly discussed. The hypothesis suggested herein is that the pore pressures are influenced by the free gases trapped during the submergence. These gases are compressed at the ambient pore pressure, which is decreasing in the flow direction. The degree of saturation and, therefore, the permeability decrease in the same direction. The pore pressures are thus higher than predicted in a uniform permeability condition. Free gases are dissolved in the water due to the increase of the pore pressures. They are carried in the seepage flow and come out of solution in the core or finally in the downstream filter after some decrease of the pore-water pressures. The increase of pore pressure with respect to the steady-state conditions is a function of many factors and is necessarily transient. Key words : pore pressure, embankment dam, unsaturated soil, permeability, seepage.