Jinhyun Choo

• Doctor of Philosophy
• Professor (Associate) at Korea Advanced Institute of Science and Technology

Computational modeling of faulting processes is an essential tool for understanding earthquake mechanics but remains challenging due to the structural and material complexities of fault zones. The phase-field method has recently enabled unified modeling of fault propagation and off-fault damage; however, its capability has been restricted to simpli...

The phase-field method has become popular for the numerical modeling of fluid-filled fractures, thanks to its ability to represent complex fracture geometry without algorithms. However, the algorithm-free representation of fracture geometry poses a significant challenge in calculating the crack opening (aperture) of phase-field fracture, which gove...

The phase-field method has become popular for the numerical modeling of fluid-filled fractures, thanks to its ability to represent complex fracture geometry without algorithms. However, the algorithm-free representation of fracture geometry poses a significant challenge in calculating the crack opening (aperture) of phase-field fracture, which gove...

Assessment of freezing effects on soil requires estimating the soil freezing characteristic curve (SFCC)—the variation of unfrozen water content with temperature. The existing methods for obtaining SFCCs often involve either costly experiments or heuristic inference from water retention data. Here, we propose a pore‐morphology‐based method for simp...

The material point method (MPM) is a hybrid Eulerian Lagrangian simulation technique for solid mechanics with significant deformation. Structured background grids are commonly employed in the standard MPM, but they may give rise to several accuracy problems in handling complex geometries. When using (2D) unstructured triangular or (3D) tetrahedral...

Geologic fractures such as joints, faults, and slip surfaces govern the stability and performance of many subsurface systems in the built environment. As such, a variety of approaches have been developed for computational modeling of geologic fractures. Yet none of them lends itself to a straightforward utilization with the classical finite element...

The water retention behavior—a critical factor of unsaturated flow in porous media—can be strongly affected by deformation in the solid matrix. However, it remains challenging to model the water retention behavior with explicit consideration of its dependence on deformation. Here, we propose a data-driven approach that can automatically discover an...

The material point method (MPM) is often applied to large deformation problems that involve sharp gradients in the solution field. Representative examples in geomechanics are interactions between soils and various “structures” such as foundations, penetrometers, and machines, where the displacement fields exhibit sharp gradients around the soil‐str...

Crack initiation, growth, and coalescence in flawed rocks have been extensively studied for 2D (planar, penetrating) flaws under uniaxial/biaxial compression. However, little is known as to the mechanisms and processes of cracking from 3D flaws under true triaxial compression, where the intermediate principal stress (σ2\documentclass[12pt]{minimal}...

The material point method (MPM) is often used to simulate soils that interact with (nearly) rigid objects, such as structures, machines, or rocks. Yet MPM simulations of such problems are quite challenging when the objects have complex shapes. In this paper, we propose an efficient approach for incorporating geometrically complex rigid objects into...

Collision‐induced stresses on soil beds under granular geophysical flows have been demonstrated to be highly erosive. However, it remains mostly elusive as to how a collisional granular flow erodes and transports soil bed material. This paper presents a combined experimental and numerical investigation into the mechanisms underlying collision‐induc...

The material point method (MPM) is frequently used to simulate large deformations of nearly incompressible materials such as water, rubber, and undrained porous media. However, MPM solutions to nearly incompressible materials are susceptible to volumetric locking, that is, overly stiff behavior with erroneous strain and stress fields. While several...

Forests cover 39% of low-altitude mountainous areas globally, and they are considered natural barriers against geophysical flows. Owing to the complexity of flows, the protective effects of forests can hardly be considered in hazard management. In this study, the interactions between granular geophysical flows and forests are explored using a MPM-D...

The failure behavior of field-scale rock masses has long been studied indirectly through laboratory compression tests on rock specimens with preexisting flaws. However, little to no attention has been paid to size effects on these cracking processes that may be governed by the relative size between the fracture process zone and the rock structure....

In this paper, the Barton–Bandis model for rock joints is extended to cyclic loading conditions, without any new material parameter. Also developed herein is an implicit solution algorithm for the extended Barton–Bandis model, which can also be used for the original Barton–Bandis model for which an implicit algorithm has been unavailable. To this e...

Despite its critical role in the study of earthquake processes, numerical simulation of the entire stages of fault rupture remains a formidable task. The main challenges in simulating a fault rupture process include the complex evolution of fault geometry, frictional contact, and off‐fault damage over a wide range of spatial and temporal scales. He...

The material point method (MPM) is frequently used to simulate large deformations of nearly incompressible materials such as water, rubber, and undrained porous media. However, MPM solutions to nearly incompressible materials are susceptible to volumetric locking, that is, overly stiff behavior with erroneous strain and stress fields. While several...

Energy walls are earth retaining structures equipped with pipe heat exchangers that harvest thermal energy sources from underground. Unlike fully embedded energy geostructures such as energy piles, energy walls interact not only with the ground but also with internal airflows under a wide range of conditions. Yet little is known as to how the inter...

In this paper, the Barton-Bandis model for rock joints is extended to cyclic loading conditions, without any new material parameter. Also developed herein is an algorithm for implicit numerical solution of the extended Barton-Bandis model, which can also be used for the original Barton-Bandis model for which an implicit algorithm has been unavailab...

Despite its critical role in the study of earthquake processes, numerical simulation of the entire stages of fault rupture remains a formidable task. The main challenges in simulating a fault rupture process include complex evolution of fault geometry, frictional contact, and off-fault damage over a wide range of spatial and temporal scales. Here,...

Granular impact—the dynamic intrusion of solid objects into granular media—is widespread across scientific and engineering applications including geotechnics. Existing approaches to the simulation of granular impact dynamics have relied on either a purely discrete method or a purely continuum method. Neither of these methods, however, is deemed opt...

We present a barrier method for treating frictional contact on interfaces embedded in finite elements. The barrier treatment has several attractive features, including: (i) it does not introduce any additional degrees of freedom or iterative steps, (ii) it is free of inter-penetration, (iii) it avoids an ill-conditioned matrix system, and (iv) it a...

We propose the convergent graph solver (CGS), a deep learning method that learns iterative mappings to predict the properties of a graph system at its stationary state (fixed point) with guaranteed convergence. The forward propagation of CGS proceeds in three steps: (1) constructing the input-dependent linear contracting iterative maps, (2) computi...

Phase-field modeling—a continuous approach to discontinuities—is gaining popularity for simulating rock fractures due to its ability to handle complex, discontinuous geometry without an explicit surface tracking algorithm. None of the existing phase-field models, however, incorporates the impact of surface roughness on the mechanical response of fr...

Geomaterials such as soils and rocks can exhibit inherent anisotropy due to the preferred orientation of mineral grains and/ or cracks. They can also be partially saturated with multiple types of fluids occupying the pore space. The anisotropic and unsaturated behaviors of geomaterials can be highly interdependent. Experimental studies have shown t...

Granular impact – the dynamic intrusion of solid objects into granular media – is widespread across scientific and engineering applications including geotechnics. Existing approaches for simulating granular impact dynamics have relied on either a pure discrete method or a pure continuum method. Neither of these methods, however, is deemed optimal f...

We present a barrier method for treating frictional contact on interfaces embedded in finite elements. The barrier treatment has several attractive features, including: (i) it does not introduce any additional degrees of freedom or iterative steps, (ii) it is free of inter-penetration, (iii) it avoids an ill-conditioned matrix system, and (iv) it a...

Crack growth and coalescence from discontinuities is the fundamental process that underlies the majority of rock mass failures. Still, however, numerical simulation of this process remains a formidable challenge. The main reasons include that tensile and shear fractures are often mixed in the cracking process, that the cracking patterns depend stro...

Phase-field modeling—a continuous approach to discontinuities—is gaining popularity for simulating rock fractures due to its ability to handle complex, discontinuous geometry without an explicit surface tracking algorithm. None of the existing phase-field models, however, incorporates the impact of surface roughness on the mechanical response of fr...

This paper presents a mixed finite element framework for coupled hydro-mechanical–chemical processes in heterogeneous porous media. The framework combines two types of locally conservative discretization schemes: (1) an enriched Galerkin method for reactive flow, and (2) a three-field mixed finite element method for coupled fluid flow and solid def...

Fracture mechanics analysis of shear band propagation requires knowledge of the material's shear fracture energy and its related properties such as the characteristic slip displacement. Yet these properties of stiff clays and shales have not been investigated systematically. This work characterizes and analyzes the shear fracture energies and chara...

Cracking of rocks and rock-like materials exhibits a rich variety of patterns where tensile (mode I) and shear (mode II) fractures are often interwoven. These mixed-mode fractures are usually cohesive (quasi-brittle) and frictional. Although phase-field modeling is increasingly used for rock fracture simulation, no phase-field formulation is availa...

Viscoplastic deformation of shale is frequently observed in many subsurface applications. Many studies have suggested that this viscoplastic behavior is anisotropic-specifically, transversely isotropic-and closely linked to the layered composite structure at the microscale. In this work, we develop a two-scale constitutive model for shale in which...

This paper presents a mixed finite element framework for coupled hydro-mechanical-chemical processes in heterogeneous porous media. The framework combines two types of locally conservative discretization schemes: (1) an enriched Galerkin method for reactive flow, and (2) a three-field mixed finite element method for coupled fluid flow and solid def...

Cracking of rocks and rock-like materials exhibits a rich variety of patterns where tensile (mode I) and shear (mode II) fractures are often interwoven. These mixed-mode fractures are usually cohesive (quasi-brittle) and frictional. Although phase-field modeling is increasingly used for rock fracture simulation, no phase-field formulation is availa...

Viscoplastic deformation of shale is frequently observed in many subsurface applications. Many studies have suggested that this viscoplastic behavior is anisotropic and closely linked to the layered composite structure at the microscale. In this work, we develop a two-scale constitutive model for shale in which anisotropic viscoplastic behavior nat...

The material point method (MPM) has been increasingly used for the simulation of large-deformation processes in fluid-infiltrated porous materials. For undrained poromechanical problems, however, standard MPMs are numerically unstable because they use low-order interpolation functions that violate the inf–sup stability condition. In this work, we d...

Geologic shear fractures such as faults and slip surfaces involve marked friction along the discontinuities as they are subjected to significant confining pressures. This friction plays a critical role in the growth of these shear fractures, as revealed by the fracture mechanics theory of Palmer and Rice decades ago. In this paper, we develop a nov...

We introduce a phase‐field method for continuous modeling of cracks with frictional contacts. Compared with standard discrete methods for frictional contacts, the phase‐field method has two attractive features: (i) it can represent arbitrary crack geometry without an explicit function or basis enrichment, and (ii) it does not require an algorithm f...

Geologic fractures such as joints and faults are central to many problems in energy geotechnics. Notable examples include hydraulic fracturing, injection-induced earthquakes, and geologic carbon storage. Nevertheless, our current capabilities for simulating the development and evolution of geologic fractures in these problems are still insufficient...

Local (element-wise) mass conservation is often highly desired for numerical solution of coupled poromechanical problems. As an efficient numerical method featuring this property, mixed continuous Galerkin (CG)/enriched Galerkin (EG) finite elements have recently been proposed whereby piecewise constant functions are enriched to the pore pressure i...

Fluid flow in isotropic porous media with one porosity scale is a well understood process and a common scenario in numerous simulations published in the literature. However, there exists a class of porous materials that exhibit two porosity scales with strong permeability contrast between the two scales. Examples of such materials are aggregated so...

We introduce a phase-field method for continuous modeling of cracks with frictional contacts. Compared with standard discrete methods for frictional contacts, the phase-field method has two attractive features: (1) it can represent arbitrary crack geometry without an explicit function or basis enrichment, and (2) it does not require an algorithm fo...

The material point method (MPM) has been increasingly used for the simulation of large deformation processes in fluid-infiltrated porous materials. For undrained poromechanical problems, however, standard MPMs are numerically unstable because they use low-order interpolation functions that violate the inf–sup stability condition. In this work, we d...

A simple approach is proposed for enabling the conventional Mohr–Coulomb plasticity to capture the effects of relative density on the behavior of dilative sands. The approach exploits Bolton's empirical equations to make friction and dilation angles state variables that depend on the current density and confining pressure. In doing so, the material...

Numerical modeling of large deformations in fluid-infiltrated porous media must accurately describe not only geometrically nonlinear kinematics but also fluid flow in heterogeneously deforming pore structure. Accurate simulation of fluid flow in heterogeneous porous media often requires a numerical method that features the local (element-wise) cons...

Liquid CO2 fracturing is a promising alternative to hydraulic fracturing since it can circumvent problems stemming from the use of water. One of the most significant differences between liquid CO2 and hydraulic fracturing processes is that liquid CO2 permeates into matrix pores very rapidly due to its low viscosity. Here we study how this rapid per...

Cracking and damage from crystallization of minerals in pores center on a wide range of problems, from weathering and deterioration of structures to storage of CO2 via in situ carbonation. Here we develop a theoretical and computational framework for modeling these crystallization-induced deformation and fracture in infiltrated porous materials. Co...

The failure behavior of geological materials depends heavily on confining pressure and strain rate. Under a relatively low confining pressure, these materials tend to fail by brittle, localized fracture, but as the confining pressure increases, they show a growing propensity for ductile, diffuse failure accompanying plastic flow. Furthermore, the r...

We synthesize the framework reported in previous works for hydromechanical analysis of coupled fluid flow-solid deformation in shale accommodating the following important features: (a) double porosity concept allowing Darcy flow to occur through the distributed microfractures and non-Darcy flow to prevail through the much smaller nanopores, (b) str...

Natural geomaterials such as fissured rocks and aggregated soils often exhibit pore size distributions with two dominant porosity scales. In fractured rocks the dominant porosities are those of the fractures and rock matrix, whereas in aggregated soils the micropores and macropores comprise the two relevant porosity scales. When infiltrated with fl...

An Arlequin poromechanics model is introduced to simulate the hydro-mechanical coupling effects of fluid-infiltrated porous media across different spatial scales within a concurrent computational framework. A two-field poromechanics problem is first recast as the twofold saddle point of an incremental energy functional. We then introduce Lagrange m...

Geomaterials with aggregated structure or containing fissures often exhibit a bimodal pore size distribution that can be viewed as two coexisting pore regions of different scales. The double porosity concept enables continuum model-ing of such materials by considering two interacting pore scales satisfying relevant conservation laws. This paper dev...

Hydromechanical interactions between fluid flow and deformation in porous geo- materials give rise to a wide range of societally important problems such as land- slides, ground subsidence, and injection-induced earthquakes. Many geomaterials in these problems possess two-scale porous structures due to fractures, particle ag- gregation, or other reaso...

This chapter investigates the relevant hydrologic and geotechnical processes triggering failure of steep hillside slopes under rainfall infiltration. Despite decades of extensive study, the fundamental controls responsible for this commonly observed slope failure mechanism are yet to be quantified. The work focuses on the triggering mechanisms of s...

The at-rest earth pressure coefficient, \(\hbox {K}_{0}\), is one of the most fundamental values for evaluating in-situ soil stresses and designing foundation. Research has been expanded to investigate the correlation between \(\hbox {K}_{0}\) and micro-scale characteristic of granular soils, beyond the macroscopic approach empirically correlated w...

Natural geomaterials such as fissured rocks and aggregated soils often exhibit a pore size distribution with two dominant pore scales, usually termed macropores and micropores. High-fidelity descriptions of these materials require an explicit treatment of the two pore regions as double porosity. We develop a finite element framework for coupled sol...

This paper describes patterns of nonlinear shear stiffness degradation with respect to the stress history of clay. An experimental study using undrained triaxial compression tests was conducted on specimens cut from reconstituted clay samples of kaolinite. The nonlinear pattern of stiffness degradation was analyzed within the frameworks of both the...

The nonlinear degradation of soil stiffness from very small to small strain is a key consideration for reliable prediction of ground behavior and its interactions with structures under dynamic excitation and working load conditions. Despite high sensitiveness of stiffness measurement to testing conditions, the effect of the pre-shear stress path on...

This paper presents a case study of deep mixing performed to improve soft ground adjacent to a historic masonry wall in an urban redevelopment site. A challenge of the site was to perform the redevelopment without impairing the masonry wall of historic importance. For the foundation of a retaining wall adjacent to the masonry wall, deep mixing was...

Soils subjected to shearing experience dilation or contraction depending on their initial porosity, and the relative displacement of individual particles determines a soil's unique particle-pore microstructure during volume change. It has been suggested that soil microstructure tends to be stabilized as pores are aligned parallel to the loading dir...

Thermal conduction in granular materials is mainly dominated by volumetric fraction of constituents, minerals that consist of grains, grain size distribution, and fine contents. Even though widely used empirical and semi-empirical correlations for thermal conductivity of granular materials capture these governing factors, the effect of applied stre...

Various factors, such as the volumetric fraction of constituents, mineralogy, and pore fluids, affect heat flow in granular materials. Although the stress applied on granular materials controls the formation of major pathways for heat flow, few studies have focused on a detailed investigation of its significance with regard to the thermal conductiv...

High quality X-ray computed microtomography (micro-CT) imaging of internal microstructures and pore space in geomaterials is often hampered by some inherent noises embedded in the images. In this paper, we introduce image calibration techniques for removing the most common noises in X-ray micro-CT, cupping (brightness difference between the periphe...

The stress condition mainly dominates the thermal conductivity of soils whereas governing factors such as unit weight and porosity suggested by empirical correlations are still valid. The 3D thermal network model enables evaluation of the stress-dependent thermal conductivity of particulate materials generated by discrete element method (DEM). The...

This paper describes the initial stiŠness of reconstituted kaolinite clay in both vertical and horizontal planes under three diŠerent stress histories. The initial shear stiŠness was obtained from bi­directional bender element tests during isotropic and K 0 stress loading and unloading. An empirical correlation was established based on the initial...

The deep mixing method, which is generally considered as a method for improving soft ground, is assessed in terms of its applicability for urban construction. Using small equipment tailored to perform deep mixing in congested urban areas, deep mixing was performed to reinforce the foundation ground of a retaining wall in a redevelopment site in Seo...

This paper presents an analysis of excavation behavior of an earth retaining wall supported by large diameter soil-cement blocks at a field trial site. The concept and design philosophy of the large soil-cement block reinforcement are described first. The wall behavior during sequential excavations up to 9.8 m is analyzed based on the measured late...