Korea University · Engineering
Professor Jong-Sub Lee's research lab specializes in geomechanics and soil dynamics, focusing on the mechanical behavior of granular materials under various conditions. The lab investigates the influence of particle characteristics—such as shape, size, and mineral composition—on soil stiffness, damping, and wave propagation. Key research directions include wave-based soil characterization, soil-structure interaction, and non-destructive evaluation of ground improvement and grouting quality using ultrasonic and electromagnetic methods. The lab combines experimental testing, advanced instrumentation (e.g., TDR, pressure plate extractors), and discrete element modeling to understand micro-mechanical mechanisms in complex soil mixtures.
Figures are computed from collected data and may differ slightly.
Bender elements are convenient shear wave transducers for instrumenting soil cells due to optimal soil–transducer coupling and compatible operating frequency. Experimental and analytical methods are implemented in this study to explore various aspects of bender element installations including: electromagnetic coupling prevention, directivity, resonant frequency, detection of first arrival, and near field effects. It is shown that electromagnetic coupling effects are critical in soils with high e
Mixtures of rigid sand particles and soft fine-grained rubber particles are tested to investigate their small and large-strain responses. Mixtures are prepared with different volumetric sand fraction sf to identify the transition from a rigid to a soft granular skeleton using wave propagation, k0 loading, and triaxial testing. Deformation moduli at small, middle, and large strains do not change linearly with the volume fraction of rigid particles; instead, deformation moduli increase dramaticall
SUMMARY A series of laboratory experiments and numerical simulations are conducted to explore the characteristics of mixtures composed of sand and rubber particles of the same median diameter. The mixtures are prepared with different volumetric sand fractions (sf = V sand /V total ). The experiment focuses on assessing the strain level on the characteristics of the mixture with the volume fraction of each component. Numerical simulations using the discrete element method are performed to obtain
The presence of mica changes the mechanical behavior of sandy soils. In this study, micro- and macroscale tests are used to explore the unique packing characteristics that develop in mixtures made of round and platy particles, and the effects that mica exerts on small, medium, and large strain parameters. Mixtures are prepared with different mica contents and various mica-to-sand size ratios, Lmica∕Dsand . Results provide a comprehensive characterization of mixtures made of spherical and platy p
The objective of this study is to estimate multiple-cycles of the soil-water characteristic curve (SWCC) using an innovative volumetric pressure plate extractor (VPPE), which is incorporated with a membrane and time domain reflectometry (TDR). The pressure cell includes the membrane to reduce the experimental time and the TDR probe to automatically estimate the volumetric water content. For the estimation of SWCC using the VPPE system, four specimens with different grain size and void ratio are
The objective of this study is to develop and apply reflection methods for guided ultrasonic waves used in evaluating the grout condition of rock bolts installed in a rock mass. Three types of rock bolts with different grouting ratios are prepared. First, piezoelectric disk elements are used as the source of guided ultrasonic waves to investigate grouted nonembedded rock bolts. Second, reflection methods with piezo disk elements and hammer impacts are used with rock bolts embedded in concrete co
Subgrade strength is an important aspect to be considered when designing unsurfaced roads and working platforms for pavement structures. Furthermore, dynamic cone penetration tests are used to characterize the subgrade strength. However, the results of dynamic cone penetration tests, including the penetration depth per blow, can be affected by transferred energy and the verticality of the cone penetrometer. The objective of this paper is to characterize the subgrade strength using an instrumente
The duration of liquefaction in small models is very short, therefore special monitoring systems are required. In an exploratory sequence of liquefaction tests, S-wave transillumination is implemented with a high repetition rate to provide detailed information on the evolution of shear stiffness during liquefaction. These data are complemented with measurements of acceleration, time-varying settlement, excess pore pressure, and resistivity profiles. Measurements show that excess pore pressure mi
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