The impact of soil-vegetation-atmosphere interaction on a landslide initiation under torrential storms: a case study

Vegetation has long been used in geotechnical engineering to protect slopes from surface instability phenomena. However, its effects remain difficult to quantify, given the diversity of plants in situ, the variability of their morpho-mechanical characteristics and their impact on soil hydraulic states. For this purpose, the case of a landslide that occurred following torrential rains in Costa Rica was analysed. After the geotechnical characterisation of the soils affected by the movement, the plant species and their main morpho-mechanical characteristics were identified. These characteristics were used to evaluate the changes in the hydromechanical parameters of the soil due to the presence of the roots, and the transpiration rates generated by the plants themselves. In the FE model, a “continuum material” approach was adopted to simulate the vegetated soil numerically, jointly with a failure criterion for partially saturated soils. Using available meteorological data, the evolution of the hydraulic state of the slope in the weeks before and during the storm that caused the landslide was simulated, comparing the cases of vegetated and hypothetically not vegetated slopes. Results validated the observations carried out on the site and confirmed the hydromechanical effects of plants in delaying in time the triggering of the landslide.