The specific research missions of our group include 1) investigating the behavior of geomaterials from low to high confining pressures, from partially to fully saturated, and from mechanical to multiphysical loading ; 2) formulating unifying mathematical frameworks to model geomaterials at grain scale and continuum scale; 3) developing computational tools to solve initial-boundary value problems that are important to engineering practices in the geotechnical, mining and energy industry.
Micro-scale mechanics of grain fracture, environmentally enhanced crack growth, and adsorption in pores:
Study the thermodynamics of fracture propagation in single particles
Model the effect of humidity and temperature on the delayed failure of grains
Understand the coupling between friction and propagation of individual microcracks
Resolve the surface forces including disjoining pressure and surface tension during fluid adsorption in nanopores and mesopores
Meso-scale evolution of particle-particle and water-particle systems:
Quantify the evolution and the asymptote of fabric tensor of granular soils upon continuous shearing
Understand the micromechanics of internal erosion in gap-graded soils
Decode the evolution of force chain structures and soil fabrics during erosion and shearing
Macro-scale continuum modelling of geomaterials: sand, rockfill, coal, claystone.
Develop Continuum Breakage Mechanics for crushable granular soils
Develop continuum damage models for anisotropic rocks
Develop critical fabric theory for unified description of quasi-static behavior of granular materials
Understand the chemistry and the mechanics of adsorption-induced deformation in microporous and mesoporous media
Laboratory testing of geomaterials under high-pressure, high-temperature environments
Field-scale finite element analysis of initial-boundary value problems:
Develop user-defined material and element subroutines
Conduct highly customized coupled thermal-hydro-mechanical-chemical analysis of complex geosystems including dams and nuclear waste repositories.
FUNDED RESEARCH PROJECTS
Project Title: Surface Forces in Subcritical Crack Growth and Healing
Role: Sole PI, Sponsor: LBNL-DOE, Duration: 2020-2021
Abstract: Subcritical crack growth (SCG) is relevant to many geological processes at different length and time scales, e.g. time- and rate- dependent deformation of brittle rocks, relaxation of internal stresses in rock systems and delayed earth ruptures. The intricate coupling between physiochemical processes (i.e. adsorption and diffusion) and mechanics (i.e. stress concentration and crack opening) at the vicinity of the crack tip, however, has never been fully resolved. Significant pressure can develop when two solid surfaces are brought close to each other (which is the case at the crack tips), causing the solid-fluid interaction zones of the two surfaces overlap. This pressure, often referred to as the disjoining pressure, can be attractive and repulsive depending on the wall separation and the fluid chemistry. Its effect on the apparent fracture toughness and crack growth kinetics has been largely ignored in fracture mechanics and SCG literatures. This pilot study focuses on testing the hypotheses that the KI necessary to propagate cracks in aqueous environment (KI0) is reduced from the intrinsic value (KIC) because of the repulsive disjoining pressure developed between the fracture surfaces.
Project Title: Time-dependent THMC properties and microstructural evolution of damaged rocks in excavation damage zone
Role: Lead PI, Sponsor: DOE-NEUP, Duration: 2018-2021
Abstract: Modeling coupled THMC processes in geomaterials near nuclear waste repositories at various time scales is an extremely challenging task and requires collaborative research effort from the field of geomechanics, hydrology and geochemistry. The proposed project focuses on the geomechanical aspect, addressing the time-dependent evolution of rock microstructure and its coupling with the THC processes that are of first-order importance to the stability and the isolation performance of the repository. This study is motivated by observing the lack of data and models linking the creep behavior of salt and argillite with microstructural changes under combined mechanical and environmental loadings. Although the use of relatively simple and time-independent material models is justified in short-term predictions, at a time scale of 1 million years, the nonlinearities of host rocks including creep, relaxation, stress corrosion and healing are expected to play a significant role in the near-field hydrology. This project delineates an integrated experimental, theoretical and numerical strategy in assessing the evolution EDZ over time and its implication on the long-term migration of hazardous species. Rock salt and argillite will be the focus of this study.
Project Title: Center for micromorphic multiphysics porous and particulate materials simulations within exascale computing workflows
Role: Senior personnel, Sponsor: ASC-NNSA-DOE, Duration: 2021-2026
Abstract: The overall objective of the Center is to simulate with quantified uncertainty, from pore-particle-to-continuum-scales, a class of problems involving granular flows, large deformations, and fracture/fragmentation of unbonded and bonded particulate materials, as well as porous cellular materials. The Center research will usher in a new era of higher fidelity multiscale multiphysics computation through large deformation micromorphic continuum field theories informed by DNS through the latest ML techniques calibrated and validated against a rich experimental data set. My role in this project is to perform experimental (at macroscale) and theoretical mechanics (at continuum level) research on the thermomechanical behavior of 1) bonded granular materials and 2) porous cellular materials with the scope of energy and defense applications.
Project Title: Caisson drilling fluid interaction with fine grained bedrock
Role: Lead PI, Sponsor: CDOT, Duration: 2018-2019
Abstract: A large number of bridges and structures in Colorado are supported by drilled caissons and shafts embedded in weak fine-grained rocks (e.g. Denver blue claystone shale and Pierre Shale). Use of these foundations has been common for decades for highway and bridge projects in Colorado but some critical knowledge gaps remain in this class of foundation engineering problems. One of them is in the empirical stipulation of a 4-hour maximum duration between the completion of drilling and placement of concrete for caissons founded on cohesive intermediate geomaterials (IGM) in CDOT’s Drill Caisson Specification 503. The proposed research attempts to study the validity of this time limit by developing a deeper understanding of the basic material aspects and correlations between the time of fluid infiltration with the two primary design inputs for drilled caissons, namely the shear strength of the bedrock and the shear resistance of the rock-concrete interface. The property of the rock, the type of the drilling fluid, and other geometrical factors will be considered in the proposed correlations. The goal is to provide a benchmark experimental database for determining a reasonable allowable time for concrete placement, and to develop an easy-to-implement procedure for integrating the drill fluid weakening effect in the design and construction of drilled shaft socketed in fine-grained rocks in Colorado.