Assessment of the use of the vapour equilibrium technique in controlled-suction tests

Abstract

This paper presents a study on suction control methodology using the vapour equilibrium technique. To reduce the time needed to reach equilibrium, humid air is forced to flow through the sample boundaries. An analysis of the physical process that occurs in the tested soil samples using a numerical approach is included. The test is numerically simulated and the key parameters of the process calibrated. A sensivity analysis of the unmeasured and variables is performed. It could be observed that forcing humid air to flow through the sample reduces the equalization time, but the results from the numerical simulations highlight that this flow must be carefully applied to avoid reaching, under steady-state conditions, a different suction than that whished for. When the circulation of air along the boundaries is slow, an increase in air velocity tends to increase the rate of suction changes in the sample. However, if the circulation of air increases over some limit, the flow conditions inside the soil control the development of process.