Large palaeo-landslides with considerable movements have sometimes caused the burial of permeable formations by the landslide mass. The pore pressure regime established in the landslide material where it overlies these permeable formations is strongly non-linear with depth. A close to hydrostatic pore pressure may be maintained down to a considerable depth, followed by a sharp drop upon approaching the base of the landslide material, to reach the pore pressure of the underlying permeable strata. This pore pressure profile is known as underdrainage profile. The paper presents the results of numerical analyses investigating the effect of inhomogeneity and anisotropy of the coefficient of permeability and infiltration from the ground surface. In order for such a non-linear pore pressure profile to exist in landslide materials there must be considerable infiltration from the ground surface and the coefficient of permeability of the landslide material must decrease with depth. This decrease is often due to the increase in vertical stress in the landslide material and also due to the orientation of clay particles along the slip surface, which may be located immediately above the upper boundary of the buried permeable formation.