Modelling Phase Transition in Saturated Granular Materials in MPM

Describing solid to fluid and viceversa granular material phase transition is crucial when simulating many natural phenomena involving soils and characterized by large displacements, such as landslides or soil liquefaction. Despite the large number of available numerical codes developed to deal with large displacements, such as those based on MPM, PFEM or SPH formulations, evident in the literature is the lack of constitutive approaches capable of simulating phase transition. This work focuses on the implementation of a constitutive model, recently conceived by the authors, in the open source MPM code ANURA3D, modified to account the hydro-mechanical coupling for. Phase transition occurrence is ruled by both void ratio and granular temperature, being this latter a state variable measuring granular agitation. The evolution of granular temperature is governed by the energy balance equation. Under saturated conditions coupling terms are added to account for water damping effects on granular agitation. The implementation is tested by simulating two undrained triaxial tests, performed on an ideal monodisperse granular specimen by changing the imposed strain rate.