• Journal of the Korean Geotechnical Society
• /
• v.29 no.8
• /
• pp.65-73
• /
• 2013

Ground-coupled heat pump system has attracted attention as a promising renewable energy technology due to its improving energy efficiency and eco-friendly mechanism for space cooling and heating. Pipes buried in the ground play a role of direct thermal interaction between circulating fluid inside the pipe and surrounding soils in the geothermal exchange system. However, both complexities of turbulent flow coupling thermal-hydraulic phenomena and very long aspect ratio of the pipe make it difficult to model the heat exchange system directly. Energy balance for fluid flow inside the pipe was derived to model thermal-hydraulic phenomena, and one-dimensional pipe element was proposed through Galerkin formation and time integration of the equation. Developed element is combined to pre-developed FEM code for THM phenomena in porous media. Numerical results of Thermal Response Test showed that line-source model overestimates equivalent thermal conductivity of surrounding soils due to thermal interaction between adjacent pipes and finite length of the pipe. Thus, inverse analysis for the TRT simulation was conducted to present optimal transformation matrix with utmost convergence.

• Journal of the Korean Geotechnical Society
• /
• v.27 no.3
• /
• pp.75-83
• /
• 2011

Emerging issues related with fully coupled Thermo-Hydro-Mechanical (THM) behavior of unsaturated soil demand the development of a numerical tool in diverse geo-mechanical and geo-environmental areas. This paper presents general governing equations for coupled THM processes in unsaturated porous media. Coupled partial differential equations are derived from three mass balances equations (solid, water, and air), energy balance equation, and force equilibrium equation. With Galerkin formulation and time integration of these governing equations, finite element code is developed to find nonlinear solution of four main variables (displacement-u, gas pressure-$P_g$), liquid pressure-$P_1$), and temperature-T) using Newton's iterative scheme. Three cases of numerical simulations are conducted and discussed: one-dimensional drainage experiments (u-$P_g-P_1$), thermal consolidation (u-$P_1$-T), and effect of pile on surrounding soil due to surface temperature variation (u-$P_1$-T).

• Journal of the Korean Geotechnical Society
• /
• v.36 no.10
• /
• pp.57-71
• /
• 2020

Liquefaction-induced sand boils were observed during the Pohang earthquake (Moment magnitude, 5.4) on November 15, 2017, specifically in the region of agricultural fields and park areas near the epicenter. This was recorded as the first observed liquefaction phenomenon in Korea. This paper analyzes liquefaction potentials at the key sites at Pohang area. The simplified methods and current design standard were used to evaluate the occurrence of liquefaction. The seismic demand was estimated based on the NGA-WEST2 ground motion prediction equations (GMPEs). The liquefaction resistance of the ground was determined using the in-situ tests: standard penetration test (SPT) and cone penetration test (CPT). The liquefaction potentials were quantified by liquefaction potential index (LPI), which were compared with those from the previous studies.

• Journal of the Korean Geotechnical Society
• /
• v.33 no.12
• /
• pp.45-58
• /
• 2017

As many seismic codes for various facilities are changed into a performance based design code, demand for a reliable nonlinear response-history analysis (RHA) arises. However, the equivalent linear analysis has been used as a standard approach since 1970 in the field of site response analysis. So, the reliability of nonlinear RHA should be provided to be adopted in replace of equivalent linear analysis. In this paper, the reliability of nonlinear RHA is reviewed for a layered soil layer using Loma Prieta earthquake records in 1989. For this purpose, the appropriate way for selecting nonlinear soil models and the effect of base boundary condition for 3D analysis are evaluated. As a result, there is no significant differences between equivalent linear and nonlinear RHA. In case of 3D analysis, absorbing boundary condition should be applied at base to prevent rocking motion of the whole model.

• Journal of the Korean Institute of Gas
• /
• v.20 no.4
• /
• pp.25-32
• /
• 2016

The purpose of this study is safety evaluation of solar energy generation which is installed on the canopy at the LPG filling station. in case of a gas station, the solar energy generation was become legalization through a related law reform in 2008. Also, in case of a LPG filling station, the solar energy generation was become legalization through a related law reform in 2015. So, the related law that KGS CODE and Safety control of dangerous substances law and the case of installed solar energy generation in gas, LPG filling station was investigated. two scenarios are supposed for the CFD. Release of safety valve pipeline and ruptured dispenser leakage are the scenarios. The FLACS which developed GexCon in Norway was used for simulation. LPG dispersion to the upper side of canopy was very small with safety distance.

• Journal of the Korean Geotechnical Society
• /
• v.35 no.6
• /
• pp.5-15
• /
• 2019

Usually, the cyclic shear stress ratio (CSR) for the assessment of liquefaction has been determined by performing ground response analysis or adopting simplified method suggested by Seed & Idriss with some modifications. In order to analyze the applicability of the CSR evaluation methods, the present study performed one-dimensional equivalent linear analysis and evaluated CSR based on design codes from FHWA, JRA, and KDS. The comparison of the CSR obtained from each code showed that the CSR from KDS showed the largest error with the analysis results. The reason is because KDS has an error, which defines the stress reduction coefficient applying the maximum acceleration at each depth, not the maximum cyclic shear stress mobilized in the soil.

• Transactions of the Korean hydrogen and new energy society
• /
• v.29 no.6
• /
• pp.596-605
• /
• 2018

Interest in hydrogen, as an energy carrier, has been growing to solve the problems on shortage of fossile fuels and greenhouse gas. According to the standard KGS FU 551 for stationary fuel cell installation, the fuel cell system could be connected up to two common exhausts to one floor. depending on the required power for building or the installation environment in buildings, multiple fuel cell systems could be installed. Afterwards the number of perforations and flues could be decided. Hence, economic efficiency in significantly determined with respect to installation area and the number of fuel cell systems. In addition, the complexity of common vent structure for stationary fuel cell systems could be changed. In this paper, Verification experiments were conducted by connecting the common exhaust system to the fuel cell simulation system and the actual fuel cell system. Humidity and temperature were changed at ON/OFF, but no factors were found to affect performance or system malfunction. Exhaust emissions were also measured to obtain optimized values. We intend to expand the diffusion of stationary fuel cells by verifying safety of common exhaust structure.

• Journal of the Korean Geotechnical Society
• /
• v.35 no.2
• /
• pp.5-17
• /
• 2019

Dynamic centrifuge model test was conducted to evaluate the dynamic stability of the pile-supported slab track method during dynamic railway loading and earthquake loading. The centrifuge tests were carried out for various condition of embankment height and soft ground depth. Based on test results, we found that the bending moment was increased with embankment height and decreased with soft ground depth. In addition, it was confirmed that the pile-supported slab track system could have dynamic stability for short-period seismic loading. However, in case of long-period seismic loading, such as Hachinohe earthquake, the observed maximum bending moment reached to pile cracking moment at the return period of 2,400 year earthquake. The criterion of ratio between embankment height and soft ground depth was suggested for dynamic stability of pile-supported slab track system.

• Journal of the Korean Geotechnical Society
• /
• v.37 no.9
• /
• pp.13-24
• /
• 2021

Recently, attempts have been made to detect fouling patterns in the ground using Ground Penetrating Radar (GPR) during the maintenance of gravel ballast railway tracks. However, dealing with GPR signal data obtained with a large amount of noise in a site where complex ground conditions are mixed, often depends on the experience of experts, and there are many difficulties in precise analysis. Therefore, in this study, a numerical modeling technique that can quantitatively simulate the GPR signal characteristics according to the degree of fouling of the gravel ballast material was proposed using python-based open-source code gprMax and RSA (Random sequential Absorption) algorithm. To confirm the accuracy of the simulation model, model tests were manufactured and the results were compared to each other. In addition, the identification of the fouling layer in the model test and analysis by various test conditions was evaluated and the results were analyzed.

• Journal of the Korean Geotechnical Society
• /
• v.38 no.8
• /
• pp.17-27
• /
• 2022

To characterize the dynamic properties of Gimhae Plains sediments, we calculated natural frequencies using microtremor horizontal-to-vertical spectral ratios and derived shear wave velocity profiles by inversion of Rayleigh-wave dispersion curves obtained by the high frequency-wavenumber and modified spatial autocorrelation methods. Our results suggest that in this region, strong amplification of ground motion is expected in the vibration frequency (f ≥ 1 Hz). Additionally, obtained velocity profiles show that shear wave velocities are ~200 and 400 m/s for the shallow marine and old fluvial sediments, respectively. Bedrock is possibly encountered at depths of 60-100 m at most sites. We developed a simplified shear wave velocity model of shallow sediments based on the obtained profiles. Our results suggest that a large area in the Gimhae Plains could be categorized as an S6 site based on the Korean seismic design code (KDS 17 10 00).