A column study of static nonequilibrium fluid pressures in sand during prolonged drainage

Abstract

In the design of layered soil systems, such as the design of liners or covers over unsaturated soil, a key design concern is the magnitude of negative fluid pressure that will develop along the base of the liner or cover. In the absence of evaporation or vapour migration, the maximum negative fluid pressures will develop near the cessation of drainage. Previous theoretical analyses and numerical modelling of these systems have indicated that this pressure will be the pressure at which an underlying sand reaches its residual water content. The hydraulic conductivity of the sand at these pressures is so small that "static" nonequilibrium pressures are sustained over long periods of time. In this note, laboratory verification is provided for the magnitude of these pressures based on drainage of a fine and coarse sand column. Key words : covers, liners, air-entry value, residual saturation, layering, drainage.