A Nonlocal Elasto-Plastic Model for Structured Soils at Large Strains for the Particle Finite Element Method

This work presents a robust and mesh-independent implementation of an elasto-plastic constitutive model at large strains, appropriate for structured soils, into a Particle Finite Element code specially developed for geotechnical simulations. The constitutive response of structured soils is characterized by softening and, thus, leading to strain localization. Strain localization poses two numerical challenges: mesh dependence of the solution and computability of the solution. The former is mitigated by employing a non-local integral type regularization whereas an Implicit-Explicit integration scheme is used to enhance the computability. The good performance of these techniques is highlighted in the simulation of the cone penetration test in undrained conditions.Peer ReviewedPostprint (published version

Chemo-mechanical Modelling in Bonded Geomaterials from the Micro- to the Macro-scale

Chemo-mechanical effects are known to influence the behavior of bonded geomaterials in a number of applications in civil, environmental and energy engineering. In this work, a two-scale constitutive model is concisely presented, in which macroscopic chemo-mechanical properties are set to mainly depend on the reactive surface area and on the cross-sectional area of cementation bonds, via two key macroscopic \u2018cross-scale\u2019 functions. The model is focused on materials with nonreactive grains and reactive bonds, such as carbonate cemented sandstones or microbially cemented silica sands. An example validation is provided, by reproducing triaxial compression tests on both loose and bio-cemented sandy soil

Plasticity with generalized hardening:Constitutive modeling and computational aspects

© Springer-Verlag Berlin Heidelberg 2016.In this work, an extended theory of plasticity with generalized hardening is proposed to describe the response of geomaterials under both mechanical and environmental processes, which include as special cases several elastoplastic constitutive equations proposed in the literature to model such processes as desaturation or suction hardening, thermal softening, chemo-mechanical coupling effects in fine-grained soils, as well as weathering of soft rocks. In the formulation of the theory, the coupling between mechanical and environmental processes takes place at two levels: first, as an additional direct contribution to the constitutive stress changes, taking place in both elastic and elastoplastic processes; and second, as a result of the evolution of the internal state variables induced by changes in the environmental process variables. This last effect is incorporated through a set of generalized hardening rules. As an example of application, the general formulation is specialized to the particular case of weak calcarenite rocks undergoing degradation processes due to plastic deformations, changes in degree of saturation (short-term debonding) and chemical dissolution of the bond material and the solid grains (long-term debonding). The resulting model is implemented in a FE code by means of an implicit generalized backward Euler algorithm, suitably modified to incorporate the full formalism of plasticity with generalized hardening. Results of numerical simulations carried out at the element level show the accuracy and efficiency properties of the proposed stresspoint algorithm. The simulation of a representative initialboundary value problem demonstrates the practical relevance of environmental degradation effects in practical applications, over periods of time comparable with the life cycle of most geotechnical structures