Constitutive modelling approach for evaluating the triggering of flow slides

The paper presents a methodology to evaluate flow slide susceptibility in potentially liquefiable sandy slopes. The proposed approach accounts for both contractive and dilative volumetric behaviour during shearing using the MIT-S1 constitutive model. As a result, it is possible to distinguish among different types of undrained response induced by a rapid shear perturbation. The first part of the paper describes the general methodology for infinite slopes, providing an index of stability for incipient static liquefaction in shallow deposits. The methodology accounts for the anisotropy due to the initial stress state and uses simple shear simulations to assess instability conditions as a function of slope angle, stress state, and density of the soil. The resulting stability charts define the margin of safety against static liquefaction and the depths likely to be affected by the propagation of an instability. The second part of the paper applies the methodology to the well-known series of flow failures in a berm at the Nerlerk site. The MIT-S1 model is calibrated using published data on Nerlerk sands and in situ cone penetration test (CPT) data. The analyses show that in situ slope angles α = 10°-13° are less than the critical slope angle needed for incipient instability. Liquefaction and flow failures were therefore promoted by small perturbations in shear stresses that could be generated by rapid deposition of hydraulic fill.