The material point method, which combines features of finite-element and particle discretisation methods, has been extended to solve coupled flow-deformation problems in granular media. The method is applied to simulate the construction and failure of the Aznalcóllar dam. The brittle foundation clay is characterised by means of a strain-softening Mohr–Coulomb elasto-plastic model. The rupture process of the foundation is associated with a progressive failure mechanism. The model predicts the development of a localised shearing band that initiates at the toe of the dam at some intermediate stage of construction, and propagates downstream and upstream. The shape and position of the failure surface reproduce actual field observations.
The paper describes a thermo-hydro-mechanical formulation to model thermally induced effects due to the irreversible work input generated during soil deformation. The model was implemented into a material point calculation procedure. The method is applied to the analysis of landslides. A simple slope stability is first analysed. Mechanical work essentially dissipates in shearing bands, which develop excess pore water pressures. The marked effect of soil permeability to control the slide motion after failure is described. Shear band thickness is also a relevant control variable. The problem posed by the non-realistic thickness of shear bands in numerical calculation is addressed by means of a numerical procedure that includes consideration of embedded shear bands where the strains are assumed to be localised. Balance equations describing local flow and thermal interactions between shear bands and the remaining material are formulated. The method is applied to model the instability and subsequent rapid motion of Vajont landslide. Calculated run-out and sliding velocity reproduce, in a satisfactory manner, field observations.
Abstract. Seismic safety of earth or rockfill dams and embankments is strongly conditioned by permanent displacements caused by earthquakes. For a severe earthquake, the permanent displacement pattern results from the combination of displacements generated by volumetric and shear plastic strains distributed within the structure, and those caused by sliding of the soil mass along one or more failure surfaces. Numerical procedures commonly used in practice do not consider the strain localization phenomena at failure surfaces and the associated mesh dependence of the solution. Typically, nonlinear finite element or finite difference codes yield an estimate of distributed deformations and dynamic response, without accounting for the plastic strain localization problem. In addition, some of the numerical approaches used in practice do not consider the change of configuration caused by large displacements. The material point method or MPM is a lagrangian "particle-mesh" numerical method. It has been previously used in modeling dynamic problems with large displacements and strain localization. With MPM, a body is discretized into a collection of lagrangian particles, which carry all the data needed to define the body's state. Interaction between particles takes place in a background fixed mesh, similar to those used in the finite element method. The MPM is applied in this paper to model the three dimensional dynamic response of Punta Negra dam, a concrete faced gravel dam which is being built in San Juan Province, Argentina..
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