Geo System Research Group (GSR), founded in 2005, focuses on developing innovative and efficient solutions in the field of geotechnical engineering through state-of-the-art computational modeling, laboratory, and field testing. Our primary interests are 1) soil dynamics and earthquake engineering, 2) soil-structure interaction, 3) energy geotechnology, and 4) soil characterization via waves. We are currently actively participating in various government and industry funded projects including, but not limited to, development of new site response algorithms, probabilistic seismic hazard analysis and generation of synthetic ground motions, seismic design of geotechnical structures, soil-fluid-structure dynamic interaction modeling, simulation of geothermal heat pump systems and thermosyphons, elastic and electrical resistivity wave based soil characterization, and multi-scale modeling of soils. We are also involved in various real engineering projects.
We try to expose our members to the state-of-the-art research and practice oriented projects, maintain a closely mentored system, and provide a cooperative but challenging environment for learning. Our goal is to equip all members with a strong foundation in fundamental theories, research capabilities with an expertise in numerical modeling, practice-oriented knowledge, and efficient communication skills.
We welcome prospective students and postdoctoral researchers with innovative ideas and hard working ethics. International researchers and students are also welcomed. For more information about the research group and potential financial support, please contact us.
ENGINEERING at HANYANG UNIVERSITY
Damage analysis results:
Damage states and damage indices are newly proposed based on the number of plastic hinge formations
Project 3: Seismic slope stability
I am involved in various projects to investigate the seismic slope stability, with a focus on cut slopes and natural mountain slopes. The research is motivated by the large percentage of natural and cut slopes in Korea. I am using dynamic analyses to investigate the Newmark displacement, which are calculated from a case specific failure surface. In previous studies, the unique failure surface dependent on both the slope and ground motion characteristics were ignored and a limit equilibrium based potential sliding surface was used. A critical development of vertical component caused by the refraction of the incident waves at the sloping soil-bedrock interface is also observed. An empirical predictive equation was proposed based on multi-variate regression analysis. I published one paper in Soil Dynamics and Earthquake Engineering and four domestic papers. The research was funded by NRF and KAIA. I am also working with Korea Electrical Power Corporation and Korea Hydro and Nuclear Power Corporation to evaluate the influence of slopes on nuclear power plants.
Nonlinear dynamic analysis simulating brittle structural collapse:
We model the inelastic behavior of concrete and reinforced steel using embedded constitutive models in LS-DYNA.
Daikai station structural failure is accurately modeled.
Project 2: Tall building – underground seismic interaction
As of 2016, I have initiated as a principal investigator a project called Development of artificial intelligence (AI) algorithm for real time damage detection of tall buildings based on accelerometer measurements. The goal of the study is to provide a tool for real-time assessment of damage for both the tall building and underground space based on the acceleration time histories. There is a need to accurately predict the tall building response for the proposed real time damage assessment. In another consulting project to perform the seismic design of triple 70 story towers in Busan (Korea) built in a huge underground space on a stiff bedrock demonstrates that the coupled tower-underground interaction is critical (Fig. 2).
Due to the enormous size of the tall building, underground space, and surrounding media, computational cost is prohibitive. I have secured the use of supercomputers for a duration of three years to eventually perform 3D full scale simulation. Preliminary analysis results demonstrate that the superstructure-underground structure interaction is very significant and critically influences the system response. Previous studies that only models the underground structure to evaluate the dynamic pressure and wall response fail to capture this important response. There is a need to understand and quantify the interaction through an extensive parametric study. There is also a need to use accurate numerical models both for the ground and structural members for such evaluation.
The importance of this approach is well recognized by the structural engineering community practicing performance-based-design in Korea. I am serving as consultants in major building projects including Hyundai Motor Group Global Business Center (100 story mega building).
The research areas in geotechnical earthquake engineering include seismic analysis of underground structures, seismic tall building-underground structure-soil interaction, seismic analysis and design of pipelines, seismic slope stability, seismic hazard assessment, numerical and physical modeling for liquefaction assessment, and seismic response of large pile groups.
Project 1: Seismic analysis of underground structures
Seismic analysis of underground structures is a topic that we have been working from the beginning of my career at Hanyang University. In a 5-year project on development of guidelines for seismic design of undersea tunnels funded by Korea Agency for Infrastructure Technology Advancement (KAIA), I have performed research on several topics. One of the topic was investigating the effect of the spatially varying ground motion on the longitudinal response of the tunnel through a pseudo-static approach that we have newly developed. Another topic was quantifying the effect of discontinuities on the structural response of subsea tunnels using discrete element analyses. The results of these studies and additional comprehensive suite of analyses were compiled and analyzed to develop practical guidelines for seismic design of subsea tunnels. In 2015, we have been awarded a 3-year project from the National Research Foundation of Korea on the topic of performance-based seismic design procedure for underground structures. It is our goal to propose a new performance-based framework for underground structures based on extensive nonlinear pseudo-static and dynamic analyses. As part of the research, new damage states and indices will be presented. The unique damage mechanism of various types of underground structures will be identified. We published a paper on the damage states and indices of cut and cover box tunnels in Bulletin of Earthquake Engineering. In the study, the damage state was newly defined as the number of plastic hinges, whereas the damage index was defined as the ratio of the elastic moment to yield moment. Currently, we are using inelastic dynamic analysis to replicate the Daikai station failure. The validated numerical model will be used for comprehensive fragility analysis of underground structures.
Project 4: Seismic analysis and design of pipelines
I have been involved in four projects on the seismic analysis and design of buried pipelines. They were funded by KAIA, Korea Infrastructure Safety and Technology Corporation Institute, and K-Water. I used three-dimensional (3D) time-domain analyses that uses nonlinear springs to simulate the pipeline-soil interaction. The impact of spatially variable ground motion on the longitudinal strain of pipelines is investigated, which is recognized as the critical seismic design parameter. The pipelines of interests include both buried gas and water pipelines. It is demonstrated that a design procedure that is widely used to estimate the damage does not provide a reliable prediction. An improved design procedure that uses the free-field displacement time histories extracted from 1D site response analyses was proposed. Current efforts include development of empirical predictive equation as functions of strain index, buried depth, and pipeline properties. I have submitted a paper to Bulletin of Earthquake Engineering on this procedure. Two domestic papers were published.
Project 4: Seismic hazard assessment and site amplification
Seismic site response is an important topic of my research group. As the original developer of 1D site response analysis program Deepsoil, which is one of the most widely used 1D nonlinear analysis program, I have been heavily involved in this research topic for a long time. I have been funded two research projects by NRF. The topics includes the development of a rate-dependent site response analysis method, use of a frequency dependent equivalent linear method, and auto-selection process of the Rayleigh damping coefficients.
The compatibility issue of the deterministically derived site coefficients used with the probabilistically calculated seismic hazard map was also a topic of interest. After two publications at Soil Dynamics and Earthquake Engineering as part of my doctoral study at University of Illinois at Urbana-Champaign, I continue to study this topic. Two journal papers on the fully probabilistic site coefficients of the deep deposits of the Mississippi Embayment were published at Bulletin of Seismological Society of America and Journal of Korean Society of Civil Engineers, respectively. I have applied this framework to Korea, where I newly perform seismic hazard analysis and derive probabilistic site coefficients. The work was published in Soil Dynamics and Earthquake Engineering.
I have worked with Professor Jonathan Stewart and Dr. Dong-Youp Kwak formerly at University of California at Los Angeles to incorporate the measured H/V ratio in the the ground motion prediction equation (GMPE), where H/V ratio is defined as the ratio of the horizontal to vertical spectral ratio. A large database of recorded motions from Kik-net and K-net in Japan were utilized to develop an additive function to a nonlinear site amplification model already implemented in GMPEs. It has been successfully demonstrated that the proposed function reduces the residual between the measured and predicted motions (Fig. 5). The work was published in Bulletin of Seismological Society of America.
I am actively involved in performing probabilistic seismic hazard analysis in Korea. A critical difficulty is defining the seismicity of Korea, due to lack of recordings and because a community derived set of seismicity parameters are not yet presented. Various approaches are undertaken to develop the seismicity data of Korea. One of my study has been published in Soil Dynamics and Earthquake Engineering. I am currently working to develop Korea specific uniform hazard response spectrum and to develop seismic hazard maps for 0.2s and 1.0s spectral acceleration.
Project 5: Numerical and physical modeling for liquefaction assessment
Liquefaction assessment in low to moderate seismic regions is a new topic that I have currently a lot interest in. The project was partly funded by NRF. My interest lies in the development of a simple yet robust pore pressure model that uses only the liquefaction resistance curve to select its input parameters. The motivation of this study is that in regions of low to moderate seismicity, use of a complex numerical simulation tool based on plasticity soil models is prohibitive. I developed a model that is based on the concept of the damage parameter and implemented it in Deepsoil. I also developed normalized liquefaction resistance curves based on extensive database that was collected. A new simple shear test device with bender elements installed to measure shear wave velocity was set up at my research group laboratory. The device was used to measure the liquefaction resistance curves of clean test sands and soil samples extracted in the field. The work was presented in two journal papers both published in Bulletin of Earthquake Engineering. I am currently working with Professor Francesco Silvestri at University of Naples and Professor Youssef Hashash at University of Illinois at Urbana Champaign on this topic.
