We proudly stand as the global leading research group specializing in seismic analysis and the design of underground structures. Our primary focus lies in exploring the inelastic response of reinforced concrete structures and the nonlinear behavior of soil. Presently, we employ high-fidelity computational models that incorporate erosion elements to accurately capture large deformations associated with structural collapse, and fiber elements to simulate inelastic responses. Our toolkit includes prominent programs such as Abaqus, LS-DYNA, DIANA FEA, OpenSees, Flac, and Plaxis.

Collaborating with numerous structural engineering research groups, we aim to transcend the boundaries of traditional geotechnical engineering. The selected topics currently under study encompass the following:

• High-fidelity simulation of the inelastic response of reinforced concrete underground structures using fiber and erosion elements

• Damage evolution of cut-and-cover and bored tunnels 

• Development of fragility curves of underground structures

• Machine learning based tools for predicting seismic performance of underground structures

Our goal is to develop numerical tools for real-time damage assessment of tall buildings and underground spaces subjected to severe earthquake loadings. Due to the enormous size of the buildings, underground spaces, and surrounding media, computational costs are prohibitive. We utilize workstations to perform 3D full-scale simulations. Analysis results demonstrate that accounting for superstructure-substructure interaction is important and critically influences the system response. Previous studies that only model the underground structure to evaluate dynamic pressure and wall response fail to capture this important aspect. There is a need to understand and quantify the interaction through an extensive parametric study. Additionally, accurate numerical models are essential for both the ground and structural members in such evaluations

• Unique superstructure - basement seismic interaction

• Seismic pressure on basement structures

• Machine learning based tools for predicting seismic performance of basements

• Development of guidelines for seismic design of basements accounting for SSI

Seismic site response constitutes a significant focus within our research group, and we have dedicated over two decades to its exploration. During this time, we have secured funding for numerous research projects from esteemed institutions including the National Research Foundation of Korea (NRF) and the Korean Hydraulic and Nuclear Power (KHNP). Our collaborative efforts extend globally, involving partnerships with renowned international institutions such as the University of Illinois at Urbana-Champaign, the University of California at Los Angeles, National Chung Hsing University, Korean Hydraulic and Nuclear Power, and UNIST. Engaging in a diverse range of projects, we address various aspects within the seismic site response domain, including the following:

• Development of high fidelity equivalent linear and nonlinear site response analysis algorithms

• Probabilistic site response analysis

• Development of unique site amplification model for shallow bedrock sites

• Utilization of H/V ratio to constrain the site amplification model

• Machine learning based tools for predicting seismic site amplification

• Utilization of site response analysis outputs for liquefaction assessment and underground structure performance estimation 

We are involved in a series of projects related to liquefaction assessment, including 1) excess pore pressure model development, 2) validation of effective stress site response analysis algorithm, and 3) magnitude scaling factor development. 

We are utilizing element level test data (cyclic simple shear test measurements) and centrifuge model test data to calibrate the pore pressure model and effective stress site response analysis method. 

We are collaborating with U of Illinois at Urbana-Champaign and U of Naples. Selected projects on liquefaction assessment are the following:

• Development of accumulated stress-based pore pressure model

• Development of normalized liquefaction curves

• Performance of effective stress analyses for liquefaction potential evaluation

• Development of magnitude scaling factor for Korea

Evaluation of seismic performance of natural and engineered slopes is important for securing resilience of transportation infrastructures. We use dynamic nonlinear finite element and finite  difference numerical models to predict the seismic response of slopes. Selected projects on liquefaction assessment are the following: 

• Calibration of 2D nonlinear model 

• Characterization of amplification characteristics and failure surface 

• Development of fragility curves

• Use of machine-learning to predict the seismic performance of slopes

Performing probabilistic seismic hazard (PSHA) is a challenge in Korea because of uncertainties in the seismicity data and ground motion models (GMMs). We are developing unique PSHA procedures tailored to fit Korean hazard maps utilizing iterative methods to adjust the earthquake catalog based seismicity. Selected projects on liquefaction assessment are the following: 

• Development of regional GMMs that accounts for the unique site amplification effects

• Use of machine learning algorithms to develop GMMs for Korea and Japan

• Generation of regional UHS

We are using high fidelity numerical models to simulate the blast-induced wave propagation and evaluate potentials for blast-induced damage to underground infrastructures. We are also developing practical methods to predict attenuation curves produced by blasting. Novel atttenuation curves for both free-field and within profile are developed which accounts for the unique near-field attenuation. We are using sophisticated models to simulate rock fracture due to blasting. State-of-the-art reinforced concrete models are being used to capture the structural damage produced by blast-induced pulses. 

We have performed extensive model tests and numerical simulations to evaluate the performance of various offshore structures including bucket, spudcan, and pile foundations. High strain penetration analyses have been performed using Coupled Eulerian Lagrangian method. We have also developed simulation-based capacity equations for bucket foundations. Global response and damage mechanism of jack-up barges under punch-through failure are in investigation.