MPM-based relationships to assess soil shear strength, velocity and runout distance of liquefaction-induced flow-type slope failures

Undrained residual shear strength (Sur) is a fundamental parameter for assessing the response of slopes consisting of liquefiable soils. Specifically, when this strength is not sufficient to ensure slope stability under static conditions, liquefaction may cause a flow-type landslide with dramatic effects on the physical environment and existing structures. The value of Sur is generally estimated using empirical relationships available in the literature, as a function of field tests data (SPT, CPT). These relationships were obtained through back-analyses conducted on numerous flow-type slope failures using simplified methodologies, such as the classical limit equilibrium method or a kinematic approach based on a sliding block model. In the present study, Sur is instead back-calculated by examining the post-failure phase of documented flow failure case studies triggered by soil liquefaction. The back-analysis is performed by means of the Material Point Method (MPM), a computational framework particularly suitable for modelling large-deformation processes in geotechnical engineering. On the basis of the results of the performed analyses, a novel equation relating Sur to the penetration resistance of the soil is presented for a more realistic evaluation of Sur than the existing relationships. Original equations are also proposed for a preliminary prediction of some parameters characterizing the evolution of the post-failure stage of flow-type slope failures, such as the velocity and runout distance, which could be useful for defining the most suitable mitigation measures.