• Journal of the Korean GEO-environmental Society
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• v.18 no.6
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• pp.5-19
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• 2017

In this study, the effect of rock mass curtain grouting was investigated by analyzing the correlation between the parameters of the RMR & grout injection volume, Lugeon value & RQD, Lugeon value & cement injection volume. In order to investigate the effect of rock mass curtain grouting, we analyzed the grout injection volume of 315 curtain grouting holes at 9 tunnel face of NATM Subsea tunnels in gneiss area. The total grout injection volume in the Subsea tunnels study was slightly changed in some tunnels face but decreased with increasing the rating of parameters in spacing of discontinuity (R3, Js) and groundwater condition (R5). The geological anomalies of seismic survey (3D, TSP) and the inflow of probe hole were found to be more correlated of relative than the parameters of RMR. The unit injection volume was found to decrease with higher ratings in the parameters of the RMR except the weathering degree of the discontinuity (Jc, R4). The correlation between RQD and Lugeon values is not significant, but it can be confirmed that the Lugeon value tends to decrease as the RQD value increases.

• Journal of the Korean Geotechnical Society
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• v.33 no.12
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• pp.45-58
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• 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 Geotechnical Society
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• v.35 no.7
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• pp.41-50
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• 2019

Gyeongju bentonite is a buffer material primarily considered in Korea and it is highly compacted as a part of an engineered barrier system (EBS) of high-level radioactive waste repository. The compacted bentonite undergoes swelling stress by groundwater penetration and thermal stress by decay heat from a canister. Therefore, the mechanical properties of the compacted bentonite buffer material is crucial for the performance assessment of EBS. This paper aims to evaluate deformation properties of Gyeongju compacted bentonite using seismic methods. Two sets of compacted bentonite specimens were prepared having dry densities of $1.59g/cm^3$ and $1.75g/cm^3$ with water contents of 10.6% and 8.7%. Free-free resonant column tests were performed to measure constrained and unconstrained compression wave velocities. With the measured wave velocities, Young's modulus ($E_{max}$) and constrained modulus ($M_{max}$), material damping ratio ($D_{min}$), and Poisson's ratio at small strain were determined. As results, this paper evaluates the deformation properties of Gyeongju compacted bentonite and compares them with the results of previous researches.

• Journal of the Korean Geotechnical Society
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• v.39 no.11
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• pp.41-51
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• 2023

This study employs three-dimensional simulation through FLAC3D to investigate the impact of installation angles on the dynamic characteristics of Triaxial Micropiles. The numerical model is validated against centrifuge test results to ensure accuracy. The findings reveal significant influences of the installation angle on the dynamic behavior of Triaxial Micropiles. Specifically, under seismic conditions such as the Capetown and San Fernando earthquakes, the lowest recorded values for peak bending moment and settlement occurred at an installation angle of 15 degrees. In contrast, when subjected to an artificial earthquake with a frequency of 2 Hz (Sine 2 Hz), Micropiles installed at 0 degrees exhibited the lowest peak bending moment, maximum axial load, and settlement values.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.6
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• pp.152-161
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• 2023

In general, large-capacity hydrogen storage vessels, typically in the form of vertical cylindrical vessels, are constructed using steel materials. These vessels are anchored to foundation slabs that are specially designed to suit the environmental conditions. This anchoring method involves pre-installed anchors on top of the concrete foundation slab. However, it's important to note that such a design can result in concentrated stresses at the anchoring points when external forces, such as seismic events, are at play. This may lead to potential structural damage due to anchor and concrete damage. For this reason, in this study, it selected an vertical hydrogen storage vessel based on site observations and created a 3D finite element model. Artificial seismic motions made following the procedures specified in ICC-ES AC 156, as well as domestic recorded earthquakes with a magnitude greater than 5.0, were applied to analyze the structural behavior and performance of the target structures. Conducting experiments on a structure built to actual scale would be ideal, but due to practical constraints, it proved challenging to execute. Therefore, it opted for an analytical approach to assess the safety of the target structure. Regarding the structural response characteristics, the acceleration induced by seismic motion was observed to amplify by approximately ten times compared to the input seismic motions. Additionally, there was a tendency for a decrease in amplification as the response acceleration was transmitted to the point where the centre of gravity is located. For the vulnerable components, specifically the sub-system (support columns and anchorages), the stress levels were found to satisfy the allowable stress criteria. However, the concrete's tensile strength exhibited only about a 5% margin of safety compared to the allowable stress. This indicates the need for mitigation strategies in addressing these concerns. Based on the research findings presented in this paper, it is anticipated that predictable load information for the design of storage vessels required for future shaking table tests will be provided.

• Economic and Environmental Geology
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• v.45 no.4
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• pp.407-429
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• 2012

There has been much debates on the geologic age of the sediments of the Domi Basin, since age results varied after research methods and fossil groups. This study carried out palynological analysis and seismic interpretation to establish a stratigraphy and environmental reconstruction mainly based on fossil dinoflagellates and Seismic data from the Domi-1 and Sora-1 wells. The dinocyst assemblages found enabled zonation of the well sediment sequence resulting in 4 ecozones. Index fossils among dinocysts and palynomorphic substances indicate geologic age of the well ranges from Eocene to Pleistocene, and paleoenvironment varies from freshwater to inner-neritic marine. The fossil association also suggests strong relationship to Japanese Tertiary basins in Kyushu area in terms of stratigraphy and basin developmental history.

• Journal of Korean Tunnelling and Underground Space Association
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• v.18 no.2
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• pp.119-128
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• 2016

In a performance-based design, the structural safety is estimated from pre-defined damage states and corresponding damage indices. Both damage states and damage indices are well defined for above-ground structures, but very limited studies have been performed on underground structures. In this study, we define the damage states and damage indices of a cut-and-cover box tunnel which is one of typical structures used in metro systems, under a seismic excitation from a series of inelastic frame analyses. Three damage states are defined in terms of the number of plastic hinges that develop within the structure. The damage index is defined as the ratio of the elastic moment to the yield moment. Through use of the proposed index, the inelastic behavior and failure mechanism of box tunnels can be simulated and predicted through elastic analysis. In addition, the damage indices are linked to free-field shear strains. Because the free-field shear strain can be easily calculated from a 1D site response analysis, the proposed method can be readily used in practice. Further studies are needed to determine the range of shear strains and associated uncertainties for various types of tunnels and site profiles. However, the inter-linked platform of damage state - damage index - shear wave velocity - shear strain provides a novel approach for estimating the inelastic response of tunnels, and can be widely used in practice for seismic designs.

• Journal of the Korea institute for structural maintenance and inspection
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• v.28 no.5
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• pp.38-46
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• 2024

In Korea, more than 60% of the population lives in apartment buildings with wall structures that exhibit brittle behavior during earthquakes. Therefore, in recent performance-based seismic design, the selection of the energy dissipation coefficient for reinforced concrete (RC) walls in nonlinear dynamic analysis is very important. Previous experimental studies have reported that the main factors affecting the energy dissipation capacity of RC walls are the axial force ratio, the spacing of transverse reinforcement of boundary element, and the aspect ratio. The Architectural Institute of Korea and the Korea Concrete Institute proposed a concentrated plastic hinge model and the energy dissipation coefficient for each RC member in the guideline 「Nonlinear Analysis Model for Performance-Based Seismic Design of Reinforced Concrete Building Structures, 2021.」 The proposed equation for the energy dissipation coefficient does not include the factors of axial force ratio and spacing of transverse reinforcement of boundary element. The aspect ratio is applied to the flexural plastic model, despite considering shear-dominated behavior. Therefore, it is necessary to examine the effect of the aspect ratio according to the analysis model. In this study, the influence of each factor on the energy dissipation coefficient was analyzed by comparing the results of existing experimental research, nonlinear analysis using the fiber element model of a nonlinear analysis program(Perform 3D), and the energy dissipation coefficient proposed in the guideline. As the axial force ratio increased, the energy dissipation coefficient decreased, and as the spacing of transverse reinforcement of boundary element decreased, the energy dissipation coefficient increased. Additionally, as the aspect ratio increased, the energy dissipation coefficient tended to increase, with the aspect ratio showing the greatest influence.

• Structural Engineering and Mechanics
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• v.3 no.2
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• pp.107-120
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• 1995

A soil-structure interaction formulation is used here which is based on consideration of the dynamics of the structure with a free, rather than a fixed, base. This approach is shown to give a quite simple procedure for coupling the dynamic characteristics of the structure to those of the foundation and soil in order to obtain a matrix formulation for the complete system. In fixed-base studies it is common to presume that each natural mode of the structure has a given fraction of critical damping, and since the interaction formulation uses a free-base model, it seems natural for this situation to assign the equal modal damping values to free-base modes. It is shown, though, that this gives a structural model which is significantly different than the one having equal modal damping in the fixed-base modes. In particular, it is found that the damping matrix resulting in equal modal damping values for free-based modes will give a very significantly smaller damping value for the fundamental distortional mode of the fixed-base structure. Ignoring this fact could lead one to attribute dynamic effects to interaction which are actually due to the choice of damping.

• Geomechanics and Engineering
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• v.31 no.3
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• pp.291-304
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• 2022

Maximum shear modulus (G_max or G₀) is an important soil property useful for many engineering applications, such as the analysis of soil-structure interactions, soil stability, liquefaction evaluation, ground deformation and performance of seismic design. In the current study, bender element (BE) tests are used to evaluate the effect of the void ratio, effective confining pressure, grading characteristics (D₅₀, C_u and C_c), anisotropic consolidation and initial fabric anisotropy produced during specimen preparation on the G_max of sand-gravel mixtures. Based on the tests results, an empirical equation is proposed to predict G_max in granular soils, evaluated by the experimental data. The artificial neural network (ANN) and Adaptive Neuro Fuzzy Inference System (ANFIS) models were also applied. Coefficient of determination (R²) and Root Mean Square Error (RMSE) between predicted and measured values of G_max were calculated for the empirical equation, ANN and ANFIS. The results indicate that all methods accuracy is high; however, ANFIS achieves the highest accuracy amongst the presented methods.