Thermal pressurization effect on landslide motion. Analysis with material point method.

Landslide motion can be affected by the thermal effects resulting from the dissipation in heat of the frictional work generated in shearing bands. This problem was initially addressed for simple landslide geometries which have to be defined a priori. In this context, these analyses assume the motion of a rigid block and the thermal-hydro-mechanical phenomena were solved at basal shearing bands and their vicinity.

Later on, in order to generalize the analysis and to face more complex geometries and features, governing equations were implemented in the material point framework. This numerical method (MPM) is able to model large strains and displacements thanks to the double discretization of the domain by means of a Eulerian computational mesh and Lagrangian material points. A new approach was proposed to deal with the pathological dependence of the frictional work generation and the computational mesh element size. The methodology consists in the definition of computational embedded joints whose thickness is defined as a material parameter. 

The presentation will show the formulation of the thermal pressurization phenomena in MPM. First, the methodology will be evaluated under triaxial conditions and simple landslide geometries using different mesh sizes.

Real cases are later analyzed and modelled in MPM. The first case refers to an incipient landslide induced by a drawdown. The potential risk of acceleration induced by thermal pressurization is analyzed. The non-accelerated behavior observed in the field is explained combining the frictional heating induced weakening with non-linear velocity dependent frictional hardening. The results show that increments of a few degrees of the frictional angle with slide velocity can counteract the heating induced acceleration. 

The second case discussed is a coseismic landslide whose acceleration and large run-out cannot be justified by means of simple strength law unless imposing an extremely and probably unrealistic strain softening.