Creep failure of landslides in partially saturated soil

Large slow-moving landslides occur worldwide in mechanically weak stratum and are sensitive to hydrological forcing, especially in climate change scenarios. They may creep slowly with slide masses slipping a few centimetres to a few metres each year and can accelerate to fail catastrophically, resulting in destruction and casualties. However, the mechanisms regulating the slow-to-fast transition toward their catastrophic collapse in the in-situ scale remain elusive. As a result, the prediction of the long-term motion of creeping landslides and transient response to hydrologic triggers relies largely on simplified models based on in-situ monitoring observations and on viscous rheology, while the dynamic coupling of time effects and matric suction in variably saturated soil under time-variable hydrologic boundary conditions is often omitted. Two slow-moving landslides instrumented with advanced monitoring networks will be collected in a case history to study the effects of external forcing, e.g. rainfall, underground water table change, water level fluctuation at the toe etc, on its slow motion; Both laboratory and in-situ creep tests will be employed to study timedependent and precursory acceleration behaviours of shear-zone soils; A numerical model with an advanced constitutive model, incorporating the effects of time and suction, will be developed to predict the slow-motion under time-dependent hydrologic conditions. An important innovation is the constitutive model, considering the effects of time and suction, for landslide materials. The evolution equation for suction links to saturation degree under time-variable hydrologic conditions during slow deformation. Moreover, the total stress is decomposed into non-Newtonian-like viscous stress and Coulomb-like friction stress. The viscous part contains a high order to capture the precursory acceleration behaviour of the soil. In this way, the transition between slowmoving behaviour (Coulomb stress dominance) and fast-moving behaviour (nonNewtonian stress dominance) can be described. Dr. Shun Wang, working as an assistant at the University of Natural Resources and Life Sciences Vienna, is the PI for this project. His research involves laboratory tests, constitutive modelling and numerical simulation. He has published around 30 peer- reviewed papers dedicated to hypoplastic constitutive models, creep behaviour of soils, and numerical modelling of natural hazards.