In this paper, a fully coupled thermo-hydro-mechanical material point method, applicable to liquid-saturated porous systems undergoing large deformations and phase transitions, is presented. A mathematical framework was established based on multiphasic mixture theory and fundamental physical conservation laws, rather than using phenomenological or semi-empirical equations. A fractional-step-based semi-implicit solution scheme was proposed to solve the coupled formulations within the framework of the generalized interpolation material point method. The proposed method was validated using several benchmark examples, including the talik closure and thaw consolidation. Its performance in simulating climate-driven large deformation problems was further demonstrated by simulating the settlement of a rigid footing on thawing ground. This paper presents an innovative and rigorous framework for predicting the impact of climate change on engineering practices.

We present a novel multiscale framework that integrates the single-point multiphase material point method (MPM) and the discrete element method (DEM) to model the complex freeze-thaw behavior of ice-bonded granular media. The proposed numerical framework is featured by (a) employing the continuum-based MPM to solve the macroscopic governing equations for granular systems involving thermo-hydro-mechanical (THM) coupling and phase transitions, and (b) using the grain-scale discontinuum-based DEM to capture the thermodynamically sensitive mechanical behaviors of ice-bonded granular media. The multiscale framework is constructed by attaching a DEM-based representative volume element (RVE) at each material point in MPM. This RVE serves as a live sample of each material point to track the state-dependent effective stress with respect to the local deformation and thermodynamic conditions like ice saturation, bridging the macroscopic phenomena and the underlying microstructural evolution. In particular, we implement a semi-implicit staggered integration scheme for the macroscale THM-coupled MPM to boost computational efficiency and enhance numerical stability. We also propose an innovative ice saturation-dependent bond contact to effectively reproduce the thermodynamically sensitive mechanical behaviors. The new multiscale framework is first benchmarked against analytical solutions for 1D non-isothermal consolidation problems. We then demonstrate its exceptional capability in simulating intricate freeze-thaw behavior of granular media through a boundary value problem involving cyclic freeze-thaw actions. Further cross-scale analyses reveal its potential in capturing key loading- and state-dependent THM responses with explainable microstructural mechanisms during complex freezing and thawing loading conditions.

The coupled thermo-hydro-mechanical (THM) response of liquid-infiltrated porous media underpins the safe operation and maintenance of key engineering infrastructure. Challenges remain in modeling and understanding the complicated multiphysics processes of porous media subjected to THM loads and undergoing large deformation. In this study, we develop a stabilized material point method (MPM) for modeling the THM responses of large deformation problems in biphasic solid–fluid mixtures. A novel and efficient staggered solution scheme is proposed to solve the governing equations of the coupled system formulated in terms of four primary variables: solid displacement (u), liquid velocity (v), pore pressure (p), and temperature (T). The scheme solves the energy balance equation first and employs the resulting temperature to further advance the calculation of the momentum and mass balance equations using a semi-implicit fractional step method to facilitate equal-order interpolations. Both the incompressible and weakly compressible fluid are considered in the presented fractional step formulations. We also develop the axisymmetric form of the coupled MPM to increase the applicability and efficiency of the method in THM problems. The validity, stability, and robustness of the proposed method are demonstrated through three benchmark problems, including the heating of a saturated half-space, the non-isothermal consolidation of a soil column, and a three-dimensional axisymmetric problem pertaining to the thermoelastic response around a point heat source. The predictive capability of the proposed method for large deformation problems is further showcased by the simulation of the progressive failure process of a thermal-sensitive slope.

Climate warming accelerates permafrost thawing, causing warming-driven disasters like ground collapse and retrogressive thaw slump (RTS). These phenomena, involving intricate multiphysics interactions, phase transitions, nonlinear mechanical responses, and fluid-like deformations, and pose increasing risks to geo-infrastructures in cold regions. This study develops a thermo-hydro-mechanical (THM) coupled single-point three-phase material point method (MPM) to simulate the time-dependent phase transition and large deformation behavior arising from the thawing or freezing of ice/water in porous media. The mathematical framework is established based on the multiphase mixture theory in which the ice phase is treated as a solid constituent playing the role of skeleton together with soil grains. The additional strength due to ice cementation is characterized via an ice saturation-dependent Mohr-Coulomb model. The coupled formulations are solved using a fractional-step-based semi-implicit integration algorithm, which can offer both satisfactory numerical stability and computational efficiency when dealing with nearly incompressible fluids and extremely low permeability conditions in frozen porous media. Two hydro-thermal coupling cases, that is, frozen inclusion thaw and Talik closure/opening, are first benchmarked to show the method can correctly simulate both conduction- and convection-dominated thermal regimes in frozen porous systems. The fully THM responses are further validated by simulating a 1D thaw consolidation and a 2D rock freezing example. Good agreements with experimental results are achieved, and the impact of hydro-thermal variations on the mechanical responses, including thaw settlement and frost heave, are successfully captured. Finally, the predictive capability of the multiphysics MPM framework in simulating thawing-triggered large deformation and failure is demonstrated by modeling an RTS and the settlement of a strip footing on thawing ground.

In rockfill dam engineering, particle breakage of rockfill materials is one of the major factors resulting in dam settlement. In this study, one-dimensional compression tests on a series of coarse granular materials with artificially-graded particle size distributions (PSDs) were carried out. The tests focused on understanding the role of initial PSDs in the dense packing density, compressibility and crushability of coarse granular materials. The effects of fractal dimension (D) and size polydispersity (θ) of PSDs were quantitatively analyzed. Two different loading stages were identified from the logarithms of the stress–strain relationships, with the turning point marked as the yield stress. A similar effect of initial PSDs was observed on the packing density and low-pressure modulus of coarse granular materials. The packing density and low-pressure modulus increased monotonically with θ, and their peak values were attained at a D value of approximately 2.2. However, there was no unique correspondence between the dense packing density and low-pressure modulus. The particle breakage was influenced differently by the initial PSDs, and it decreased with the values of D and θ. The emergence of the unique ultimate state was also identified from both the compression curves and PSDs of the samples after the tests. The potential implications of the test results in the design of both low and high rockfill dams were also demonstrated.

Bridging the mechanical response of rockfill materials with laboratory grading curves and field grading curves is of obvious importance in rockfill dam engineering and has been a great challenge for geotechnical researchers for decades. In this study, a novel approach was proposed to consider the scale effect on the volumetric behavior of rockfill materials. The proposed scale effect model was incorporated into an existing volume-stress equation and was validated by both the experimental data in the literature and the one-dimensional compression test results performed by the authors. Furthermore, it was demonstrated that the single scale-related parameter in the model, namely, the Weibull modulus m, obtained experimentally from the particulate scale, can also be applied for granular assemblies. This work provides not only a theoretical framework to understand the scale effect on the volumetric behavior of rockfill materials but also a very promising application in rockfill dam engineering: one can effectively estimate the volumetric behavior of a rockfill material with the field grading curve using simply experimentally obtained volume-stress data of a downscaled material and the single-particle crushing tests data of the composing rockfill particles. (c) 2020 American Society of Civil Engineers.

Particle breakage of granular materials is a phenomenon of great importance in engineering practices. This paper presents a unified particle breakage model for granular materials, which is able to capture the evolution of the particle size distribution (PSD) of each size fraction of particles. A novel experimental technique using dyed gypsum particles (DGPs) to track the fractional particle breakage was first adopted in the one-dimensional compression tests. A unique path of the fractional particle breakage, regardless of whether the particles were in a polydisperse medium or in other different granular assemblies, was then experimentally identified. This result has inspired the introduction of the definition of a fractional breakage index, based on which the breakage-plastic work relationship for overall granular assemblies was extended to describe the fractional particle breakage. The established fractional particle breakage model differs from most existing particle breakage models in that it is able to capture both the evolution of the fractional and the overall PSDs of granular materials, even when the initial PSD of the granular material surpassed partially the theoretical fractal PSD. These results set a vision to predict and understand the particle breakage of granular materials in industrial activities. (C) 2020 Elsevier Ltd. All rights reserved.

Observing the fragmentation of individual particles within granular assemblies is a subject of evident theoretical and practical importance. A new technique using dyed gypsum particles (DGPs) to match the broken particles to their parents was adopted in this study. An image-based method of acquiring the shape information of particles from two orthogonal views was proposed. The mass survival probability and shape characteristics of the children particles were analyzed after a series of one-dimensional compression tests on the DGPs. It was found that medium-sized particles in the polydisperse samples underwent more breakage than the other particles, and this might have been attributed to the combined effects of the particle crushing strength and the coordination number. The shape evolution of broken particles and surviving particles showed opposite trends. Because the particles after the test within a given size range consisted of both the broken and surviving particles, their overall shape characteristics did not show a consistent trend. Furthermore, individual particle crushing tests on the children particles suggested that the breakage-induced shape irregularity did not change the Weibull modulus, but had a substantial effect on the magnitude of the survival probability.

Gap-graded soil-rock mixtures (SRMs), composed of coarse-grained rocks and fine-grained soils particles, are very inhomogeneous materials and widely encountered in geoengineering. In geoengineering applications, it is necessary to know the compaction characteristics in order to estimate the minimum void ratio of gap-graded SRMs. In this paper, the void ratios of compacted SRMs as well as the particle breakage during vibrating compaction were investigated through a series of vibrating compaction tests. The test results show that gap-graded SRMs may reach a smaller void ratio than the SRM with a continuous gradation under some circumstances. When the particles in a gap interval play the role of filling components, the absence of them will increase the void ratio of the SRM. The particle breakage of gap-graded SRMs is more prominent than the SRM with continuous gradation on the whole, especially at the gap interval of 5–20 mm. Based on the test results, a minimum void ratio prediction model incorporating particle breakage during compaction is proposed. The developed model is evaluated by the compaction test results and its validation is discussed.