Rainfall infiltration in a landslide soil deposit: Importance of inverse particle segregation

• Particle segregation in the landslide process is a mechanism for soil heterogeneity.
• Field investigations were performed to characterize particle segregation in two slopes.
• The particle size and permeability are quantified as non-stationary random fields.
• Particle segregation affects the infiltration in the upper part of the slope significantly.

Coarse particles move towards the front and surface of the deposit, while fine particles stay in the rear and bottom. Accordingly the coefficient of permeability of the soil statistically tends to decrease from the surface to the bottom and from the toe to the apex of the deposit. This feature can be described by trend functions that describe the changes in particle size and permeability inside the soil deposit. In this paper, attempts are made to include the physical background in the characterization of geotechnical uncertainties. The objectives of this paper are to simulate non-stationary fields of particle size and coefficient of permeability in a landslide soil deposit, and to analyse rainfall infiltration in the non-stationary random fields. The soil deposit is assumed to consist of inter-layers parallel to the slope surface. The soil deposit is also assumed to be axisymmetric; therefore, any vertical section of the deposit can be selected to generate two dimensional non-stationary random fields. Each of the non-stationary random fields is formulated by adding a trend surface to a residual stationary random field with orthogonal major and minor scales of fluctuation. The produced random fields follow an exponential correlation structure. Subsequently, steady-state rainfall infiltration in the anisotropic non-stationary heterogeneous random fields is analysed. The effects of variations of saturated permeability and scale of fluctuation on the pore-water pressure regime are also investigated.