Research Interests
Research Interests
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Observation and characterization of contacts
Observation and characterization of contacts
As the granular contact behavior is strongly dependent on surface roughness, this study addresses quantitative characterization of roughness of sand grain surfaces, and its influence on the contact maturing process. This research confirms a rich texture of sand grain surfaces by microscopic observations using Scanning Electron Microscopy (SEM) and Atomic Force Microscope (AFM). With the surface profiles obtained from AFM, this study not only examines the typical amplitude surface roughness parameters, but also identified spatial roughness parameters, e.g., the Power Spectral Density (PSD) analysis. Three grain testing is conducted to quantitatively characterize the time-dependent changes of surface morphological features before and after contact maturing. In the grain-scale laboratory experiments, the grain deflection over time is heavily dependent on the initial roughness of sand grains. The tests will be advanced under complex but realistic loading conditions over time to investigate the nature of contact evolution.
Discrete modeling of contacts
Discrete modeling of contacts
This study focuses on development of mathematical framework, allowing more confident engineering design. The discrete models, distinct element model (DEM) and discrete asperity model (DAM), are capable of capturing the time-dependent contact process that is difficult to track in physical testing. I would like to develop a complete numerical model by improving the discrete approaches, which is vital for up-scaled field analyses. The model outcome, time-dependent contact-to-contact response to sustained loads, is employed as a building block for granular assembly analysis including numerous granular contacts.
Long-term grain split under sustained loading
Long-term grain split under sustained loading
Subcritical fracturing of individual particles alters physical properties of the entire grain assembly, resulting in new constitutive behavior. This has long been recognized as a possible cause of the time-dependent behavior in granular soils. While considerable effort has been devoted to the short-term crushing behavior of individual sand grains in the literature, few studies focused on time-dependent grain splitting caused by subcritical crack propagation. I will explore the consequences of stress-corrosion cracking on long-term grain splitting. Preliminary study on the subcritical grain split indicates completely different failure mode and internal crack development, compared to abrupt grain crushing. The delayed fracture of grain is controlled by internal flaws, which I want to investigate alongside with delayed comminution at contact.
instant_rev.mp4sustain_rev.mp4Stability analysis of geotechnical structures
Stability analysis of geotechnical structures
This study analyzes the stability of geotechnical structures such as slopes, foundations, retaining walls, and tunnels. The goal of this research is to take into account realistic behaviors of soils and rocks associated with non-classical strength envelopes, and address very practical engineering problems. While the traditional Mohr-Coulomb failure envelope is preferred by many due to its simplicity and conservative manner, true behavior of soils and rocks is nonlinear with truncated tensile strength. Application of nonlinear failure condition to real world geotechnical stability analysis is of particular interest to me. Based on the consequence, a versatile, efficient, and compatible library of geotechnical structure analysis is built, and this will become a software eventually.
GIS (Geographic Information Systems)-based natural hazards modeling
GIS (Geographic Information Systems)-based natural hazards modeling
Practical analyses of natural hazards such as earthquakes, landslides, and debris flows are often performed by distributed modeling at regional scale. This allows much more rapid and cost effective ways for disaster mitigation, as the GIS framework describes the whole behavior of disasters in a wide area. In my previous study, successful predictions of rainfall induced landslides and debris flows at regional scale were possible with an automatic algorithm and key inputs: geotechnical, geomorphological, geological, and hydrological databases. To this end, the emerging technologies, for instance, data mining, machine learning, computer vision, and unmanned aerial vehicle (UAV) data collection are new opportunities, and I am looking forward to actively pursuing such approaches. I also want to make use of well-developed national databases by the U.S. Geological Survey (USGS), National Oceanic & Atmospheric Administration (NOAA), and National Weather Service (NWS) collaborating with other disciplines, e.g., earth science, geomatics, and climatology.
Consolidation analysis
Consolidation analysis
This study aims to estimate the efficacy of the pile foundation system in in-homogeneous soils. The multi-layer consolidation analysis is conducted using the finite different method with special care in the layer interface. The time-dependent settlement can be simulated under increasing construction loading that differs from one-step instant loading.
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