A COLUMN STUDY OF STATIC NONEQUILIBRIUM FLUID PRESSURES IN SAND DURING PROLONGED DRAINAGE

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 o f negative fluid pressure that will develop along the base of the line r or cover. In the absence of evaporation or vapour migration, the max imum negative fluid pressures will develop near the cessation of drain age. Previous theoretical analyses and numerical modelling of these sy stems have indicated that this pressure will be the pressure at which an underlying sand reaches its residual water content. The hydraulic c onductivity 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 th ese pressures based on drainage of a fine and coarse sand column.