Distributed quantitative risk Analysis for Rapid Flow-like Landslides induced by high Intensity Storm

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Goal

Develop a reliable strategy to quantitatively assess the hazard associated with rainfall-induced rapid landslides

Research

Landslide impact on man-made works

Lombardia region is characterized by a landslide-prone topography: mountain and hilly territories represent more than 50% of the total area. Rapid flow-like landslides, defined in the scientific literature as flow slides, fast soil movements and debris flows are the most frequent types of landslides occurring in Lombardia region (about 41%). These landslides are triggered by heavy rainfall where water plays an important role both in the inception  and the propagation phase. As well known, these kind of landslides are particularly destructive natural events. Those consequences are due to the fragile response of the material when the process initiates, to the limited or no premonitory signs, and to the enormous potential damage associated with:

  • the large volumes of soil involved,
  • the high velocity reached by the fluidized materials
  • the long travelling distances (up to several kilometers).

These events can cause serious social, environmental and economic consequences. In Lombardia they have been among the major cause of casualties and the same in other regions as suggested by the 1998 Sarno and 2009 Messina events with 160 and 37 casualties, respectively.

Hence, the risk assessment related to these landslides is of primary importance both in the development of land use policies, in the prevention of damages at structure and infrastructures and loss of lives.
Unfortunately, despite the significant progress made in the last two decades in the understanding of the triggering processes and of the hydro-mechanical processes governing the mechanics of free surface gravitational flows of granular materials, there is still much work to do in the quantitative evaluation of the hazard and risk assessment associated with this kind of natural phenomena and reduction of the mitigation countermeasures costs.

The project will provide a methodological path to define the potential unstable volume, the propagation, the arrest and the possible interaction with existing structures, infrastructures or protective works. This could sign a major step forward with respect to common rainfall thresholding by differentiating sources according to the triggering probability and the expected evolution (sliding or flowing). Guidelines for the optimization of the design of mitigation measures will be also provided.

It is apparent that, due to the high complexity and catastrophic relevance of the problem, a multidisciplinary approach must be followed. Thus the project is conceived as interdisciplinary research bridging geology, engineering geology, hydrology and climate change modelling, soil mechanics, mathematics, physics, fluid dynamics and computational mechanics.

The research units of Politecnico di Milano and Università di Milano Bicocca, leaded by Prof. Claudio di Prisco and Prof. Paolo Frattini, respectively, will cooperate to reach this goal. The two teams are complementary since they approach the same physical problems by using different and fully combinable techniques.

Action lines

Data collection and geodatabase: Mapping of past landslide events and description of triggering mechanisms, return period, and intensity. Study of rainfall patterns in Lombardia and creation of probability maps of extreme rainfall. Identification and characterization of a homogeneous area of potential triggering of rapid flow-like landslides, in the framework of a GIS environment.

Analysis of the inception: Development of a probabilistic geotechnical model to estimate the probability of occurrence of rainfall-induced rapid flow-like landslides. This model will account for the hydrogeological response of the system, the variation of the Safety Factor (SF) as a function of rainfall infiltration, water content and soil suction, and the evolution mode (sliding or flowing).

Analysis of the propagation: Quantitative parametric analysis of the propagation processes by employing advanced numerical models, such as MPM, SPH and PFEM and suitable material rheologies. Simulation of future possible scenarios in Regione Lombardia.

Interaction with structures: Definition of an approach for evaluating the impact forces on structures and optimization of the design of risk mitigation measures, such as sheltering structures/embankments.

The entire project will be structured in full agreement with Lombardia Region and Civil Protection authorities.