Hui-Hai Liu's Research Highlights
Fingering flow and mixing of variable density contaminants in porous media.
Collaborator: Dr. Jacob H. Dane, Auburn University
Density variability occurs in many subsurface-contaminant transport problems. Our major contributions in this area include developing and validating criteria for gravitational instabilities, experimentally revealing different unstable behavior of variable density contaminants, and developing numerical approaches for dealing with the unstable contaminant transport processes. My Ph.D. thesis documenting these contributions was selected as the best Ph.D. thesis of the year by Soil Science Society of America.
Fractal-Based characterization and simulation of subsurface heterogeneity.
Collaborator: Dr. Fred J. Molz, Clemson University
Subsurface heterogeneity and its effect on subsurface contaminant transport have been key research topics for many years. Our major contributions in this area include for the first time reporting the multifractal behavior of permeability distributions, demonstrating the Levy-fractal behavior of permeability distributions in fractured rock, revealing the scale-dependency of Levy index when using Levy fractals for characterizing subsurface heterogeneity, and also developing a number of fractal-based approaches for characterizing and modeling subsurface heterogeneity. These contributions have been very well received in the subsurface hydrology community.
Flow and transport in unsaturated fractured rock.
Collaborator: Scientists at LBNL
Flow and transport in unsaturated fractured rock is an important issue for both subsurface contaminant transport and geological disposal of nuclear wastes, and also one of the most challenging research topics in the subsurface hydrology. Our major contributions in this area include developing new constitutive relations for fracture networks, proposing a new upscaling method of constitutive relations for unsaturated tuff matrix, and extending random walk particle methods from a single continuum to dual-continua. Especially, we developed an active fracture model for describing preferential flow, and theoretically demonstrated the consistency of the model with fractal flow patterns often observed in unsaturated systems. While how to model flow and transport in unsaturated fractured rock remains an issue of current debate, the active fracture model has been one of the most widely used models in this area. U.S. Department of Energy has also used it as a primary model for modeling flow and transport in the unsaturated zone of Yucca Mountain, Nevada, the proposed location for a nuclear waste repository in the United States.Matrix diffusion and scale-dependency of the effective matrix diffusion coefficient.
Collaborator: Scientists at LBNL; Dr. Fred J. Molz at Clemson University
Matrix diffusion has been a classic research topic in fracture hydrology because of its importance for retarding solute transport. We for the first time reported the potential scale-dependency of the effective matrix diffusion coefficient, which has significant implications for understanding and modeling contaminant transport processes in fractured rocks.
Coupled hydrological and mechanical processes in the subsurface.
Collaborator: Scientists at LBNL (Drs. Jonny Rutqvist and James G. Berryman)
Coupled hydrological and mechanical processes are important for many practical applications including nuclear waste disposal and CO2 geological sequestration. My contribution in this area is the development of a general relationship between stress and elastic strain for porous and fractured rock, based on a hypothesis that a natural rock consists of “hard” and “soft” parts and different parts follow different varieties of Hooke’s law. This development allows for unifying a large number of empirical relationships between stress and mechanical properties within a rather simple theoretical framework. Modeling large-scale coupled hydrological and mechanical processes is currently a major research activity in this area.