Laboratory tests for permeability of sand during liquefaction

The permeability is a very important property affecting drainage, pore pressure buildup and dissipation, and ground settlement for saturated sand during and after seismically induced liquefaction. A laboratory experiment was developed to conduct tests for evaluating the water movements and permeability in a sand column before, during and after liquefaction. The excess pore water pressures at various depths within the sand specimen, hydraulic gradients, and water flow rates were recorded continuously throughout the tests. The permeability of the sand specimen during the process of liquefaction was calculated from these measurements. Results showed that the permeability of fine Vietnam sand during liquefaction was about 4-5 times the initial value before liquefaction, while it reduced to 0.9-0.97 times the initial value after complete dissipation of the excess pore pressures depending on the density of sand. The permeability of sand during excess pore pressure dissipation after liquefaction was also evaluated.