Landslide triggering

The Hydromechanical Landslide Triggering Model


The landslide triggering model computes for each simulated time step the average water content in each soil column by partitioning rainfall into infiltration, surface runoff, matrix flow and fast flow along the soil-bedrock interface. The water content, in turn, affects the soil mechanical strength (and the mass of wet soil) and accordingly the force balance for each soil column. Assuming that a soil column behaves as a rigid block and the potential slip plane is located at the soil-bedrock interface, the driving force for a single column is calculated as the sum of the downslope component of the weight of the soil column and the force exerted by neighboring columns. The resisting forces include friction and cohesion at the soil-bedrock interface. When the driving force at the base exceeds the resisting force, the soil column fails at the base (reducing the soil strength at the base to the residual value). The excess load (difference between the driving force and the residual soil strength) is then assigned to the upslope neighboring columns through interconnecting mechanical bonds with bond strength equal to soil tensile strength τt (reinforced by root cohesion croot in forested area). The tensile strength is defined by the following equation based on the Mohr-Coulomb failure criterion [Goodman, 1980]:      
                                                          

with friction angle φ, water density ρw, gravitational acceleration g, capillary pressure h and soil cohesion csoil . The coefficient χ defines the ratio between capillary strength and capillary pressure, approximated by the degree of effective saturation according to the model of Lu et al. [2010].

A redistributed load that exceeds bond strength results in failure of the lateral bonds. When all the lateral mechanical bonds connecting a column to its upslope neighbors fail, the excess load is transferred to the downslope columns as a compressive load. When the compressive load exerted on the downslope column exceeds their intrinsic compressive strength τc, the load bearing soil column fails and is released as a landslide (typically cascading to neighboring column failures). Following Goodman [1980] the compressive strength is defined as:

More details of the model procedure are described as a flow chart as shown below.

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