From grain to specimen scale laboratory soil testing towards sustainable mitigation works against flow-like landslides

Soil deformation and failure have been extensively investigated in the last decades, while the specific topic of liquefaction and fluidization (in saturated or unsaturated soils) was marginally analysed due to the complexity of the topic and because of the lack of proper experimental devices and techniques. It is remarkable that liquefaction and fluidization are the key processes to transform a soil-slip into a flow-like landslide, and to produce huge damage and threat.

The scientific literature highlights that rainfall increases the pore water pressures, which are positive when the soil is fully saturated and negative when the soil is unsaturated (i.e. a mixture of solid particles, voids filled with water and voids filled with air). The increase of pore water pressures reduces the effective normal stresses in the solid skeleton of the soil and thus, the soil deformability is increased and the soil cohesion is lowered. This means that a soil may deform and slide along a slope during a rainstorm. Even more, soil may undergo liquefaction (effective stresses into the solid skeleton become null) and fluidization (the soil starts to behave as a viscous-like fluid), if the micro-structure of the soil is collapsible. This is the case of air-fall deposits (like volcanic pyroclastic soils or wind-transported loess deposits). Currently, when an area is assessed as unstable or marginally stable, this area is necessarily considered as susceptible to flow. It means that the mitigation works can be heavily overestimated and unsustainable, with huge damage to the environment and landscape. This poor evaluation of natural hazards is certainly unacceptable to date, and deserves huge scientific efforts.

The research programme will contribute to combine the experimental X-ray tomography technique (Grenoble) with advanced testing devices (Salerno). This can lead to a general improvement of the seepage analysis and stress-strain modelling of soil behaviour.

The main impact of the project is to merge the experimental, theoretical and practical capabilities of the two groups to improve the analysis of peculiar soil mechanical behaviour leading to catastrophic landslides and related phenomena. Damage to the environment and landscape can be reduced if the assessment of the soil mechanical behaviour is improved, through a proper analysis of the behaviour at micro-scale and also an adequate analysis of liquefaction and fluidization of soil.