Fully coupled elastoplastic hydro-mechanical analysis of unsaturated porous media using a meshfree method

This paper presents the first application of an advanced meshfree method, ie, the edge-based smoothed point interpolation method (ESPIM), in simulation of the coupled hydro-mechanical behaviour of unsaturated porous media. In the proposed technique, the problem domain is spatially discretised using a triangular background mesh, and the polynomial point interpolation method combined with a simple node selection scheme is adopted for creating nodal shape functions. Smoothing domains are formed on top of the background mesh, and a constant smoothed strain, created by applying the smoothing operation over the smoothing domains, is assigned to each smoothing domain. The deformation and flow models are developed based on the equilibrium equation of the mixture, and linear momentum and mass balance equations of the fluid phases, respectively. The effective stress approach is followed to account for the coupling between the flow and deformation models. Further coupling among the phases is captured through a hysteretic soil water retention model that evolves with changes in void ratio. An advanced elastoplastic constitutive model within the context of the bounding surface plasticity theory is employed for predicting the nonlinear behaviour of soil skeleton. Time discretisation is performed by adopting a three-point discretisation method with growing time steps to avoid temporal instabilities. A modified Newton-Raphson framework is designed for dealing with nonlinearities of the discretised system of equations. The performance of the numerical model is examined through a number of numerical examples. The state-of-the-art computational scheme developed is useful for simulation of geotechnical engineering problems involving unsaturated soils.     

Self-repair of cracks and defects in clay: a review of evidence,mechanisms, theories and nomenclature

Clay minerals and clayey soils have been extensively researched over the last century leading to a rich and still evolving corpus of knowledge on clay chemistry, microstructure and macroscopic behaviour. Clay has the ability, under certain conditions, to spontaneously repair its cracks. However, despite ample evidence, clay self-repair remains understudied and under-theorised. For example, the majority of experimental studies discussing clay self-repair infer its existence from changes to macroscopic properties assumed to be caused by self-repair, and only a small number of studies have attempted to observe self-repair directly. This paper reviews the literature on clay self-repair. First, it situates clay self-repair within the broader context of self-repairing material. Next, autogenous self-repair of clay, under wet-dry cycles, freeze–thaw cycles and deep-ground consolidation, is presented focusing on evidence, driving mechanisms and key variables of influence. Next, theories of clay self-repair proposed in the literature are discussed, highlighting their scope and limitations, as well as the extent to which they have been validated by experimental observations. Key gaps in current knowledge of clay self-repair are highlighted and ways in which they can be addressed in future research are proposed. Finally, a nomenclature distinguishing between different kinds of clay self-repair is proposed based on eight different attributes.