• Earthquakes and Structures
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• v.24 no.1
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• pp.65-79
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• 2023

A simplified analytical solution for seismic response of tunnel cross section in horizontally layered ground subjected to oblique incidence of SH wave is deduced in this paper. The proposed analytical solution consists of two main steps: free-field response in layered field and tunnel response. The free field responses of the layered ground are obtained by one-dimensional finite element method in time domain. The tunnel lining is treated as a thick-wall cylinder to calculate the tunnel response, which subject to free field stress. The analytical solutions are verified by comparing with the dynamic numerical results of two-dimensional ground-lining interaction analysis under earthquake in some common situations, which have a good agreement. Then, the appropriate range of the proposed analytical solution is analyzed, considering the height of the layered ground, the wavelength and incident angle of SH wave. Finally, by using the analytical solutions, the effects of the ground material, burial depth of the tunnel, and lining thickness and the slippage effect at the ground-lining interface on the seismic response of tunnels are investigated. The proposed solution could serve as a useful tool for seismic analysis and design of tunnels in layered ground.

• Journal of Electrical Engineering and Technology
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• v.4 no.4
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• pp.531-537
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• 2009

Lightning has a broad frequency spectrum from DC to a few MHz. Consequently, the high frequency performance of grounding systems for protection against lightning should be evaluated, with the distributed parameter circuit model in a uniform soil being used to simulate grounding impedances. This paper proposes a simulation method which applies the distributed parameter circuit model for the frequency-dependent impedance of vertically driven ground rods by considering multi-layered soil structures where ground rods are buried. The Matlab program was used to calculate the frequency-dependent ground impedances for two ground rods of different lengths. As a result, an increase of the length of ground rod is not always followed by a decrease of grounding impedance, at least at a high frequency. The results obtained using the newly proposed simulation method considering multi-layered soil structures are in good agreement with the measured results.

• Journal of the Korean GEO-environmental Society
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• v.24 no.10
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• pp.51-58
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• 2023

The dynamic behavior of the group piles supporting the superstructure in an earthquake is influenced by different complex dynamic mechanisms by the inertia force of the superstructure and the kinematic force of the ground. In an earthquake, The dynamic p-y curve is used to analyze the dynamic behavior of the pile foundation in consideration of the interaction of the ground, pile foundation, and superstructure due to the inertia force and the kinematic force. Most of the research has been conducted in order to confirm the dynamic p-y curve of the pile foundation by applying to the pile foundation installed on the single layered ground consisting of sand and clay, but the research for the multiple layered ground is insufficient. In this study, 1g shaking table tests were conducted to analyze the effect of the strata ratio of the top and bottom ground of the two layered sandy ground which has different relative densities on the dynamic behavior of group piles supporting the superstructure. The result shows that the maximum acceleration in the ground, the pile cap, and the superstructure increases as the strata ratio increases, and the location of the maximum bending moment of the pile foundation is changed. In addition, it was confirmed that the slope of the dynamic p-y curve of the pile foundation increased and decreased according to the strata ratio.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2005.03a
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• pp.47-51
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• 2005

If a structure is founded on the ground saturated with pore water, then the ground should be modeled as a saturated two-phase porous medium for accurate earthquake response analysis. In this study, an axisymmetric transmitting boundary hyperelement is developed for modeling of far field of the ground using u-U formulation for water-saturated transversely isotropic layered stratum. The developed hyperelement is verified by comparing the dynamic stiffness of rigid circular foundation on water-saturated isotropic layered stratum with the case of using equivalent single-phase medium model.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.83-90
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• 2001

The site effects of local geological conditions on seismic ground motion are performed using 2D numerical method. For the analysis, a numerical method far ground response analysis using FE-BE coupling method is developed. The total system is divided into two parts so called far field and near field. The far field is modeled by boundary element formulation using the multi-layered dynamic fundamental solution that satisfied radiational condition of wave. And this is coupled with near field modeled by finite elements. In order to verify the seismic response analysis, the results are compared with those of commercial code. As a result, it is shown that the developed method can be an efficient numerical method to solve the seismic response analysis of the site effect in 2D problem.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.10
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• pp.71-80
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• 1996

Sattering problem of electromagnetic waves by periodic strip grating with two dielectrics over a ground plane in case of oblique incidence and arbitrary polarization is analyzed by the vector floquet mode expansion method and the moment mehtod from the viewpoint of soft and hard boundary value problem. To confirm proposed analysis methods, we examine the solution convergence for the scattering problem. And some numerical results of artificially soft and hard surfaces using the structure filled with single dielectric slab between periodic strip grating and gorund plane is compared with previous results. Some interesting results for soft and hard surfaces using periodic strips loaded with two layered dielectric slabs over a ground plane are given.

• Geomechanics and Engineering
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• v.33 no.4
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• pp.369-380
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• 2023

The aim of this paper is to investigate stress analysis of semi-infinite soils consisting of two layers with twin rectangular tunnels under static loads. The region close to the ground surface and tunnel modelled within finite elements. In order to use a more realistic model, the far region is modelled within infinite elements. The material model of the layered soil is considered as elastic and isotropic. In the finite element solution of the problem, two dimensional (2D) plane solid elements are used with sixteen-nodes rectangular finite and eight-nodes infinite shapes. Finite and infinite elements are ordered to be suitable for the tunnel and the soils. The governing equations of the problem are obtained by using the virtual work principle. In the numerical process, the five-point Gauss rule is used for the calculation of the integrations. In order to validate using methods, comparison studies are performed. In the numerical results, the stress distributions of the two layered soils containing twin rectangular tunnels presented. In the presented results, effects of the location of the tunnels on the stress distributions along soil depth are obtained and discussed in detail. The obtained results show that the locations of the tunnels are very effective on the stress distribution on the soils.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.117-124
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• 2002

The major purpose of this study is to determine the dynamic behavior of soil-pile-structure interaction system considering the underground cavity. For the analysis, a numerical method fur ground response analysis using FE-BE coupling method is developed. The total system is divided into two parts so called far field and near field. The far field is modeled by boundary element formulation using the multi-layered dynamic fundamental solution that satisfied radiational condition of wave. And this is coupled with near field modeled by finite elements. For the verification of dynamic analysis in the frequency domain, both forced vibration analysis and free-field response analysis are performed. The behavior of soil non-linearity is considered using the equivalent linear approximation method. As a result, it is shown that the developed method can be an efficient numerical method to solve the seismic response analysis considering the underground cavity in 2D problem.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2006.03a
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• pp.345-350
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• 2006

If a structure is founded on the ground saturated with pore water, then the ground should be modeled as a saturated two-phase porous medium for accurate earthquake response analysis. In this study, a 3-dimensional transmitting boundary is developed for modeling of far field using u-U formulation for water-saturated transversely isotropic layered stratum. The developed transmitting boundary is verified by comparing the dynamic stiffness of rigid square foundation on water-saturated isotropic layered stratum with the case of using equivalent single-phase medium model.

• Geomechanics and Engineering
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• v.32 no.6
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• pp.553-566
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• 2023

A circular tank foundation resting on the ground and subjected to axisymmetric horizontal and vertical loads and moments is analyzed using the variational principles of mechanics. The circular foundation is assumed to behave as a Kirchhoff plate with in-plane and transverse displacements. The soil beneath the foundation is assumed to be a multi-layered continuum in which the horizontal and vertical displacements are expressed as products of separable functions. The differential equations of plate and soil displacements are obtained by minimizing the total potential energy of the plate-soil system and are solved using the finite element and finite difference methods following an iterative algorithm. Comparisons with the results of equivalent two-dimensional finite element analysis and other researchers establish the accuracy of the method.