Evaluation of hydraulic conductivity in the slip zone of an earthflow in clay shales

Discontinuities and inhomogeneities can significantly influence soil permeability. The study of such influence is very important for landslides, in which permeability controls distribution and response of pore water pressures to rain. In order to evaluate if the slip surface affects permeability distribution in clayey earthflows, field tests were carried out in the head zone of an earthflow of the Italian Apennines. In a number of boreholes, the water level was lowered and the inflowing discharge was evaluated locally, by an ad hoc apparatus, along the whole height of the boreholes. The results of the experimentation show that in a narrow band around the slip surface the specific discharge is much higher than elsewhere. The permeability along the shear band was evaluated by interpreting experimental data by a commercial FEM code (SEEP/W). The model was used to simulate both the localized tests and standard tests of rapid water table lowering followed by spontaneous rising. The results provide permeability values kb for the shear band one-two orders of magnitude higher than in the landslide body kl. The high values of permeability in the shear band are supposed to influence significantly the kinematic response of the earthflow to variations in the hydraulic boundary conditions.