• Journal of the Korean Geotechnical Society
• /
• v.22 no.1
• /
• pp.25-34
• /
• 2006

In this study an effective stress numerical procedure is used to assess the results of dynamic centrifuge tests under high effective stress. The centrifuge models consist of loose Nevada sand with an initial vertical effective stress of 380kPa at depth, and they are modeled as a one-dimentional soil column. Liquefaction occurred up to 37m or 22m at depth, and the onset of liquefaction triggering was opposite to the conventional liquefaction evaluation procedure. In other words, liquefaction occurs first at the top and propagates downward as shaking continues. The results observed in centrifuge tests are reasonably predicted by the effective stress model. It is noted that the degree of initial saturation and additional densification at depth arising from the application of the high acceleration field play a key role in capturing the results of dynamic centrifuge tests.

• Journal of the Korean Geotechnical Society
• /
• v.34 no.5
• /
• pp.53-63
• /
• 2018

Dynamic soil-pile interaction is the main concern in the design of group piles under earthquake loadings. The lateral resistance of the pile group under dynamic loading becomes different from that of a single pile due to the group pile effect. However, this aspect has not yet been properly studied for the pile group under seismic loading condition. Thus, in this study the group pile effect was evaluated by performing a series of dynamic centrifuge tests on $3{\times}3$ group pile in dry loose sand. The multiplier coefficients for ultimate lateral resistance and subgrade reaction modulus were suggested to obtain the p-y curve of the group pile. The suggested coefficients were verified by performing the nonlinear dynamic analyses, which adopted Beam on Nonlinear Winkler Foundation model. The predicted behavior of the pile group showed the reasonable agreement compared with the results of the centrifuge tests under sinusoidal wave and artificial wave.

• Geotechnical Engineering
• /
• v.23 no.3
• /
• pp.21-28
• /
• 2007

• Journal of the Korean Geotechnical Society
• /
• v.34 no.8
• /
• pp.15-26
• /
• 2018

Recently, as the seismic performance based design methods have been introduced, dynamic numerical analyses need to be performed to evaluate the actual performance of structures under earthquakes. The verification of the numerical modeling is the most important for the performance based design. Therefore, 2-dimensional numerical analyses were performed to simulate the seismic behavior of a pile-supported structure, to provide the proper numerical modeling and to determine of input parameters. A dynamic centrifuge test of a pile group in dry loose sand was simulated to verify the applicability of the numerical model. The numerical modeling was carefully made to reflect the actual condition of the centrifuge test including dynamic soil properties, soil-pile interaction, boundary condition, the modeling of the group pile and structure and so on. The predicted behavior of the numerical analyses successfully simulated the acceleration variation in ground, the moment and displacement of the pile, and the displacement and acceleration of the structure. Therefore, the adopted numerical modeling and the input parameters can be used to evaluate the seismic performance of pile groups.

• Journal of the Korean Geotechnical Society
• /
• v.36 no.11
• /
• pp.61-70
• /
• 2020

In dynamic centrifuge tests, equivalent shear beam (ESB) container minimizes the boundary effect between the soil model and the wall of the container so as to effectively simulate the boundary conditions of real field state. The ESB container at KAIST was evaluated to be performing properly by Lee et al. (2013). However, it is necessary to re-evaluate the performance of ESB container since the ESB container may have deteriorated over time. Thus, the performance of eight-year-old ESB container was re-evaluated through dynamic centrifuge tests. Firstly, the natural period of the empty ESB container was compared with the results of Lee et al. (2013). Then the boundary effect of sand-filled ESB container was evaluated. Results show that the dynamic behavior of the sand-filled ESB container was similar to that of the ground, despite a decrease in the natural period of the empty ESB container over time. In addition, the dynamic response of the ground built in the ESB container and the same ground simulated through numerical analysis with free-field boundary conditions were similar. Therefore, it was found that the boundary effect of the ESB container due to the decrease in the natural period was not significant.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.28 no.4
• /
• pp.202-211
• /
• 2016

This study aims to analyze seismic responses of suction foundations for offshore wind turbine. For this purpose, dynamic centrifuge model tests were carried out. The skirt length of the suction foundation is a critical element for bearing mechanism against environmental loads. Thus, dynamic centrifuge model tests were performed and analyzed for three suction foundation models with the ratios of skirt length to suction foundation diameter of 0.5, 0.75, and 1 installed in dense sand. As results, the acceleration amplification at the suction foundation, residual settlement, and residual tilting angle were compared.

• Land and Housing Review
• /
• v.5 no.1
• /
• pp.35-40
• /
• 2014

Site coefficient and amplification factor of current domestic Seismic Design Code (KBC-2009) have no consideration for the domestic ground condition in which the base rock is normally placed within 30m form the surface. Accordingly, in this study dynamic centrifugal test and analysis for pile foundation into sand and upper structure were achieved. and the response spectrums of free surface and basement were compared with each other. Within the period 1 sec., the measured spectral acceleration of free surface and basement was bigger than the design spectral acceleration of SC and SD site. However the measured spectral acceleration of free surface and basement for the period over 1.5 sec. was smaller than the design spectral acceleration of SC site. There was no severe difference of spectral acceleration according to the upper structure, embedded depth of foundation and free surface conditions. Consequently, normal domestic apartment housing for the period range over 1.5sec. could be design more economically applying these test result.

• Journal of the Korean Geotechnical Society
• /
• v.22 no.5
• /
• pp.59-67
• /
• 2006

The centrifuge and 1-g shaking table tests were performed simultaneously to compare the dynamic behaviors of loose sands of the same geotechnical properties. The prototype soils were 10 m thick liquefiable loose sands. The geometric scaling factors were 20 for 1-g and 40 for centrifuge tests. The excess pore pressure, surface settlement, and acceleration in the soil were measured at the same locations in the 1-g and centrifuge tests. The total excess pore pressure from development to dissipation was measured. In the centrifuge test, viscous fluid was used as the pore water to eliminate the time scaling difference between dynamic time and dissipation time. In the 1-g tests, the steady state concept was applied to determine the unit weight of the model soil, and two different time scaling factors were applied for the dynamic time and the dissipation time. It is concluded that the 1-g tests can simulate the excess pore pressure of the prototype soil if the permeability of the model soil is small enough to prevent dissipation of excess pore pressure during shaking and the dissipation time scaling factor is properly determined.

• Journal of the Korean Geotechnical Society
• /
• v.32 no.3
• /
• pp.39-47
• /
• 2016

In this study, dynamic centrifuge tests in dry sand were conducted in order to evaluate the effect of pile installation on the dynamic p-y curve. According to the result of the pile installation effect on the dynamic p-y backbone curves, the subgrade resistance of a jacked pile in 40 g was found to be greater than that of a jacked pile in 1 g and a preinstalled pile in 1 g. It was also found that differences of the subgrade resistance decrease with the depth of the pile. Applicability of dynamic p-y backbone curve for the bored pile proposed by preceded researcher was evaluated by comparing with the result of centrifuge tests. In addition, dynamic p-y backbone curve for jacking/driven pile was developed by modifying that for the bored pile.

• Journal of the Korean Geotechnical Society
• /
• v.33 no.6
• /
• pp.5-16
• /
• 2017

Rocking behavior of shallow foundation during the earthquake can reduce the seismic load of the superstructure. The dynamic centrifuge tests were performed to investigate the availability of using rocking behavior for the weathered soil condition. The centrifuge test model was composed of the weathered soil, shallow foundation and single degree of freedom structure. And the accelerations of soil, foundation and structure, and the foundation settlement were measured during the earthquake. From the test result, the seismic load of the structure for the strong earthquake input was reduced by the rocking behavior with foundation uplift and the maximum foundation settlement was less than 0.5% of the foundation width. This shows the potential that the rocking foundation concept can be used in the economical seismic design of foundation for the weathered soil in the future with additional research and verification.