Modelling Water Flow and Ion Transport in Clay Soils: The Case of KCl Wells in the Head of an Earthflow

This paper shows the results of the numerical modelling of water flow and ion propagation occurring in a test field of KCl wells installed in a landslide of the southern Italian Apennines. Preliminarily, oedometer and direct shear tests on specimens exposed to KCl were carried out in laboratory; ion diffusion and related time-dependent increase in residual shear strength were modelled by a commercial FEM code. Then, the processes occurring in the test field were analysed. The specific discharge profile q(z) along the well height in steady-state conditions and the transient water level restoring h(t) after a rapid drawdown were observed, monitored and modelled. For an axisymmetric domain, a permeability distribution interpreting both q(z) and h(t) in each borehole was determined. Thus, a 3D model of the entire test field was calibrated in MODFLOW-3D FDM code. The results of the experimental/numerical analysis show that, under natural hydraulic potentials, ion propagation from the wells is governed by water flow along a narrow band surrounding the slip surface, much more permeable than the soil above and beneath. Two years after the beginning of the experimentation, the increase in pore ion concentration is noticeable in the monitoring verticals, 5m far from the KCl wells.