Numerical simulation of pore water pressure effects on landslides - case study of Nanka in southeastern Nigeria

Rainfall-induced landslides remain a major geohazard in Nigeria, particularly in the southeastern region. These landslides typically occur at the beginning and end of the rainy seasons each year, as well as during periods of high-intensity rainfall. This study focuses on the Nanka gully erosion site, where the rate of gully expansion exceeds that of other gullies within Anambra State in the southeastern region. A simplified finite element analysis of the site was conducted using PLAXIS 2D to examine the influence of climate and subsoil profile on slope stability. The effect of climate was simulated by applying net inflow/outflow, which is the difference between precipitation and potential evapotranspiration for the reported period, at the ground surface in a coupled flow-deformation analysis. The safety factor, a crucial indicator of slope stability, was calculated at selected time instances and examined in relation to the beginning and end of the rainy seasons, as well as varying rainfall intensity and duration. This preliminary study utilised a Mohr-Coulomb failure criterion, with an emphasis on the unsaturated hydraulic behaviour of the soil. The findings of the studies are discussed in this paper to reflect the impact of these variables on the susceptibility of Nanka slopes to landslides.