Dynamics of water movements with reversals in unsaturated soils

The Soil Water Characteristic Curve (SWCC) is the most important information needed to analyse, describe and compute the hydraulic and mechanic behavior of unsaturated soils. Using conventional laboratory testing methods, usually the SWCC is measured for equilibrium conditions by controlling either the pressure in the air or water phase. Already since several years it is well known that during transient processes dynamic effects are existing leading to an overshoot of the SWCC during drainage and an undershoot during imbibition. Against this background, the validity of the conventionally measured SWCC for describing transient processes is at least to be questioned. Measurements conducted during transient multi-step-inflow- And -outflow-experiments have revealed another manifestation of dynamic effects in form of accumulation of water with repeating imbibition and drainage cycles. These observations were possible only by simultaneous measurements of water content profiles using a novel measurement method based on Time Domain Reflectometry and local pore water pressure measurements using micro tensiometers. Calculations with a Lattice Boltzmann Method based code confirms the existence of this new kind of dynamic effects for unsaturated soils.