Search for: All records

The mechanical behavior of unsaturated porous media under non-isothermal conditions plays a vital role in geo-hazards and geo-energy engineering (e.g., landslides triggered by fire and geothermal energy harvest and foundations). Temperature increase can trigger localized failure and cracking in unsaturated porous media. This article investigates the shear banding and cracking in unsaturated porous media under non-isothermal conditions through a thermo–hydro–mechanical (THM) periporomechanics (PPM) paradigm. PPM is a nonlocal formulation of classical poromechanics using integral equations, which is robust in simulating continuous and discontinuous deformation in porous media. As a new contribution, we formulate a nonlocal THM constitutive model for unsaturated porous media in the PPM paradigm in this study. The THM meshfree paradigm is implemented through an explicit Lagrangian meshfree algorithm. The return mapping algorithm is used to implement the nonlocal THM constitutive model numerically. Numerical examples are presented to assess the capability of the proposed THM mesh-free paradigm for modeling shear banding and cracking in unsaturated porous media under non-isothermal conditions. The numerical results are examined to study the effect of temperature variations on the formation of shear banding and cracking in unsaturated porous media. 

Abstract Dynamic shearing banding and fracturing in unsaturated porous media are significant problems in engineering and science. This article proposes a multiphase micro‐periporomechanics (PPM) paradigm for modeling dynamic shear banding and fracturing in unsaturated porous media. Periporomechanics (PPM) is a nonlocal reformulation of classical poromechanics to model continuous and discontinuous deformation/fracture and fluid flow in porous media through a single framework. In PPM, a multiphase porous material is postulated as a collection of a finite number of mixed material points. The length scale in PPM that dictates the nonlocal interaction between material points is a mathematical object that lacks a direct physical meaning. As a novelty, in the coupled PPM, a microstructure‐based material length scale is incorporated by considering micro‐rotations of the solid skeleton following the Cosserat continuum theory for solids. As a new contribution, we reformulate the second‐order work for detecting material instability and the energy‐based crack criterion and J‐integral for modeling fracturing in the PPM paradigm. The stabilized Cosserat PPM correspondence principle that mitigates the multiphase zero‐energy mode instability is augmented to include unsaturated fluid flow. We have numerically implemented the novel PPM paradigm through a dual‐way fractional‐step algorithm in time and a hybrid Lagrangian–Eulerian meshfree method in space. Numerical examples are presented to demonstrate the robustness and efficacy of the proposed PPM paradigm for modeling shear banding and fracturing in unsaturated porous media. 

ABSTRACT In this article, we formulate a computational large‐deformation‐plasticity (LDP) periporomechanics (PPM) paradigm through a multiplicative decomposition of the deformation gradient following the notion of an intermediate stress‐free configuration. PPM is a nonlocal meshless formulation of poromechanics for deformable porous media through integral equations in which a porous material is represented by mixed material points with nonlocal poromechanical interactions. Advanced constitutive models can be readily integrated within the PPM framework. In this paper, we implement a linearly elastoplastic model with Drucker–Prager yield and post‐peak strain softening (loss of cohesion). This is accomplished using the multiplicative decomposition of the nonlocal deformation gradient and the return mapping algorithm for LDP. The paper presents a series of numerical examples that illustrate the capabilities of PPM to simulate the development of shear bands, large plastic deformations, and progressive slope failure mechanisms. We also demonstrate that the PPM results are robust and stable to the material point density (grid spacing). We illustrate the complex retrogressive failure observed in sensitive St. Monique clay that was triggered by toe erosion. The PPM analysis captures the distribution of horst and graben structures that were observed in the failed clay mass. 

Strain localization and cracking in porous media are significant issues in engineering and science. Periporomechanmics is a strong nonlocal framework for modeling the mechanics and physics of porous media with evolving discontinuities. In periporomechanics, the horizon that usually lacks a physical meaning serves as a nonlocal parameter. In this article, as a new contribution, we formulate a Cosserat periporomechanics paradigm incorporating a micro-structure related length scale for modeling shear banding and cracking in dry porous media. In this new Cosserat-periporomechanics framework, each material point is endowed with both translational and rotational degrees of freedom following the Cosserat continuum theory. We formulate a stabilized Cosserat constitutive correspondence principle through which classical micro-polar constitutive models for porous media can be used in Cosserat periporomechanics. We have numerically implemented the Cosserat periporomechanics paradigm through an explicit Lagrangian meshfree algorithm. We first present numerical examples to validate the implemented computational Cosserat periporomechanics paradigm for modeling shear bands and cracks. We then present numerical examples to demonstrate the efficacy and robustness of the Cosserat periporomechanics for modeling the shear banding bifurcation and crack branching in dry porous media. 

Abstract Dynamic crack branching in unsaturated porous media holds significant relevance in various fields, including geotechnical engineering, geosciences, and petroleum engineering. This article presents a numerical investigation into dynamic crack branching in unsaturated porous media using a recently developed coupled micro‐periporomechanics (PPM) paradigm. This paradigm extends the PPM model by incorporating the micro‐rotation of the solid skeleton. Within this framework, each material point is equipped with three degrees of freedom: displacement, micro‐rotation, and fluid pressure. Consistent with the Cosserat continuum theory, a length scale associated with the micro‐rotation of material points is inherently integrated into the model. This study encompasses several key aspects: (1) Validation of the coupled micro‐PPM paradigm for effectively modeling crack branching in deformable porous media, (2) Examination of the transition from a single branch to multiple branches in porous media under drained conditions, (3) Simulation of single crack branching in unsaturated porous media under dynamic loading conditions, and (4) Investigation of multiple crack branching in unsaturated porous media under dynamic loading conditions. The numerical results obtained in this study are systematically analyzed to elucidate the factors that influence crack branching in porous media subjected to dynamic loading. Furthermore, the comprehensive numerical findings underscore the efficacy and robustness of the coupled micro‐PPM paradigm in accurately modeling dynamic crack branching in variably saturated porous media. 

This paper characterizes nanoscale soil-water retention mechanism of unsaturated clay through molecular dynamics simulation. Series of molecular dynamics simulations of clay at low degrees of saturation were conducted. Soil water was represented by a point cloud through the centre-of-massmethod. Water-air interface area was measured numerically by the alpha shape method. Spatial variation of water number density is characterized and used to determine the adsorbed water layer. The soil-water retention mechanism at the nanoscale was analysed by distinguishing adsorptive pressure and capillary pressure at different mass water contents and considering apparent interface area (water-air interface area per unit water volume).