• Structural Engineering and Mechanics
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• 제10권4호
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• pp.299-312
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• 2000

The response of an embedded body to dynamic loads is greatly influenced by the reactions of the soil to the motion of the body. The properties of the soil surrounding embedded bodies (e.g., piles) may be different than those of the far-field for a variety of reasons. It may be weakened or strengthened according to the method of installation of piles, or altered due to applying one of the soil strengthening technique (e.g., electrokinetic treatment of soil, El Naggar et al. 1998). In all these cases, the shear strength of the soils and its shear modulus vary gradually in the radial direction, resulting in a radially inhomogeneous soil layer. This paper describes an analysis to compute vertical and torsional dynamic soil reactions of a radially inhomogeneous soil layer with a circular hole. These soil reactions could then be used to model the soil resistance in the analysis of the pile vibration under dynamic loads. The soil layer is considered to have a piecewise, radial variation for the complex shear modulus. The model is developed for soil layers improved using the electrokinetic technique but can be used for other situations where the soil properties vary gradually in the radial direction (strengthened or weakened). The soil reactions (impedance functions) are evaluated over a wide range of parameters and compared with those obtained from other solutions. A parametric study was performed to examine the effect of different soil improvement parameters on vertical and torsional impedance functions of the soil. The effect of the increase in the shear modulus and the width of the improved zone is investigated.

• Geomechanics and Engineering
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• 제34권5호
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• pp.529-545
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• 2023

The coupled soil-pile-structure seismic response is recently in the spotlight of researchers because of its extensive applications in the different fields of engineering such as bridges, offshore platforms, wind turbines, and buildings. In this paper, a simple analytical model is developed to evaluate the dynamic performance of seismically isolated bridges considering triple interactions of soil, piles, and bridges simultaneously. Novel expressions are proposed to present the dynamic behavior of pile groups in inhomogeneous soils with various shear modulus along with depth. Both cohesive and cohesionless soil deposits can be simulated by this analytical model with a generalized function of varied shear modulus along the soil depth belonging to an inhomogeneous stratum. The methodology is discussed in detail and validated by rigorous dynamic solution of 3D continuum modeling, and time history analysis of centrifuge tests. The proposed analytical model accuracy is guaranteed by the acceptable agreement between the experimental/numerical and analytical results. A comparison of the proposed linear model results with nonlinear centrifuge tests showed that during moderate (frequent) earthquakes the relative differences in responses of the superstructure and the pile cap can be ignored. However, during strong excitations, the response calculated in the linear time history analysis is always lower than the real conditions with the nonlinear behavior of the soil-pile-bridge system. The current simple and efficient method provides the accuracy and the least computational costs in comparison to the full three-dimensional analyses.

• 대한원격탐사학회지
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• 제11권3호
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• pp.117-127
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• 1995

본 논문에서는 지표면의 유효 토양 수분함유량의 적정한 값을 추출하는 몇가지 방법을 소개하고 그 방법들을 서로 비교하였다. 지표면의 꼭대기 층은 비교적 말라 있고, 밑바닥 층은 젖 어 있어서 종단면으로 봤을 때 토양은 대개 균일하지 않은 수분함유량 분포를 갖는다. 이러한 비 균일적인 토양의 수분함유량을 봤을 때 토양은 대개 균일하지 않은 수분함유량 분포를 갖는다. 이러한 비균일적인 토양의 수분함유량을 어떤 평균적인 값으로 나타낸 것이 유효 수분함유량이 다. 이 유효 수분함유량을 구하는 간단한 방법 중의 하나는 층층이 측정한 수분함유량의 산술 평 균을 취하는 것이다. 다른 방법으로는 균일한 지표면과 비균일한 지표면의 침투 두께를 각각 계 산하고 비교하여 유효 수분함유량을 얻는 방법이 있다. 또 다른 방법은 균일 지표면과 비균일 지 표면에서 각각 반사율을 계산하고 비교하여 유효 수분함유량을 구한다. 이러한 방법들이 서로 비 교되었고, 특히 반사율 적용법이 좀 더 자세하게 연구되었는데 그 이유는 실제 레이다 산란은 전 파의 침투보다는 반사에 의해 좌우되기 때문이다.

• 한국군사과학기술학회지
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• 제2권1호
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• pp.30-37
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• 1999

흙으로 침투하는 전파의 투과도와 흙에 의한 신호감쇄량을 계산하였다 대상 복합매질을 이층구조로 모델링한 후, 적분형태로 주어진 전계 표현식을 보였다. 불균일 복합매질에서는 체적산란이 일어나며, 이의 영향이 감안된 전파특성을 분석하기 위하여 반복법인 본(Born) 근사법을 사용하였다. 또한 불균일 복합매질이 가진 랜덤성의 정도는 분산과 상관길이에 의해 정해지도록 하였다. 흙에 함유된 수분량, 흙 입자의 반경, 온도 및 주파수를 변수로 하는 투과도 및 신호감쇄량 식을 제안하였다. 제안된 식으로부터 이들 변수에 따른 투과도 및 신호감쇄량의 변화를 보였다. 분석 결과, 수분이 함유된 경우에는 신호감쇄량의 변동폭이 온도에 따라서 크게 달라짐을 보게 되었고, 그 변동치는 일반적인 예상치를 훨씬 초과하였으며 그 물리적 이유를 설명하였다.

• Geomechanics and Engineering
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• 제36권2호
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• pp.167-181
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• 2024

The soil-structure relative stiffness is a key factor affecting the seismic response of underground structures. It is of great significance to study the soil-structure relative stiffness for the soil-structure interaction and the seismic disaster reduction of subway stations. In this paper, the dynamic shear modulus ratio and damping ratio of an inhomogeneous soft soil site under different buried depths which were obtained by a one-dimensional equivalent linearization site response analysis were used as the input parameters in a 2D finite element model. A visco-elasto-plastic constitutive model based on the Mohr-Coulomb shear failure criterion combined with stiffness degradation was used to describe the plastic behavior of soil. The damage plasticity model was used to simulate the plastic behavior of concrete. The horizontal and vertical relative stiffness ratios of soil and structure were defined to study the influence of relative stiffness on the seismic response of subway stations in inhomogeneous soft soil. It is found that the compression damage to the middle columns of a subway station with a higher relative stiffness ratio is more serious while the tensile damage is slighter under the same earthquake motion. The relative stiffness has a significant influence on ground surface deformation, ground acceleration, and station structure deformation. However, the effect of the relative stiffness on the deformation of the bottom slab of the subway station is small. The research results can provide a reference for seismic fortification of subway stations in the soft soil area.

• 조명전기설비학회논문지
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• 제29권4호
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• pp.95-101
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• 2015

This paper presents experimental results about characteristics of soil discharge as a function of moisture content when the $1.2/50{\mu}s$ lightning impulse voltage is applied. The laboratory experiments, for this study, were carried out based on factors affecting the transient behavior in soils. The electrical breakdown in soils was measured over a 0-6% range of moisture content for sands and a 0-4% range of moisture content for gravels. Needle-plane electrode systems was used As a result, the conduction current prior to ionization growth in dry soil is a little, but it in wet soil is increased with the applied voltage because the wet soil particles act as conductors. The soil impedance curves show an abrupt reduction just after breakdown. The general tendency measured in different soils is that the higher the water content, the lower the breakdown voltage and the shorter the time-lag to breakdown.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 가을 학술발표회 논문집
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• pp.257-266
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• 1999

This paper presents a method of seismic analysis for a cylindrical liquid storage structure on/in horizontally layered half.space considering the effects of the interior fluid and exterior soil medium in the frequency domain. To capture the essence of fluid-structure-soil interaction effects effectively, a mixed finite element with two-field (u, p) approximation is employed to model the compressive inviscid fluid, while the structure and soil medium are presented by the 3-D axisymmetric finite elements and dynamic infinite elements. The present FE-based method can be applied to the system with complex geometry of fluid region as well as with inhomogeneous near-field soil medium, since it can directly model both the fluid and the soil. For the purpose of verification, dominant peak frequencies in transfer functions for horizontal motions of cylindrical fluid storage tanks with rigid massless foundation on a homogeneous viscoelastic half.space are compared with those by two different added mass approaches for the fluid motion. The comparison indicates that the Present FE-based methodology gives accurate solution for the fluid-structure-soil interaction problem. Finally, as a demonstration of versatility of the present study, a seismic analysis for a real-scale LNG storage tank embedded in layered half.space is carried out, and its member forces along the height of the structure are compared with those by an added mass approach developed by the present writers.

• Geomechanics and Engineering
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• 제16권6호
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• pp.609-618
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• 2018

A new mechanical model for predicting the vibration of a pipe pile embedded in longitudinally layered visco-elastic media with radial inhomogeneity is proposed by extending Novak's plain-strain model and complex stiffness method to consider viscous-type damping. The analytical solutions for the dynamic impedance, the velocity admittance and the reflected signal of wave velocity at the pile head are also derived and subsequently verified by comparison with existing solutions. An extensive parametric analysis is further performed to examine the effects of shear modulus, viscous damping coefficient, coefficient of disturbance degree, weakening or strengthening range of surrounding soil and longitudinal soft or hard interbedded layer on the velocity admittance and the reflected signal of wave velocity at the pile head. It is demonstrated that the proposed model and the obtained solutions provide extensive possibilities for practical application compared with previous related studies.

• Journal of applied mathematics & informatics
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• 제6권3호
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• pp.809-822
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• 1999

We consider the mathematical model of a resource-based autotroph-herbivore system where diffusion of nutrient within the soil is taken into account. We have derived the conditions for the existence of steady-state to the system and studied the stability and instability of the patially homogeneous case. Then we have introduced the diffusion term to the system and studied the qualitative behabviour of the spatially inhomogeneous case. Finally we have discussed the salient features of the analytical results giving also the ecological interpretations.

• Geomechanics and Engineering
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• 제12권5호
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• pp.849-862
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• 2017

With growing interests in using bacterial biopolymers in geotechnical practices, identifying mechanical properties of soft gel-like biopolymers is important in predicting their efficacy in soil modification and treatment. As one of the promising candidates, dextran was found to be produced by Leuconostoc mesenteroides. The model bacteria utilize sucrose as working material and synthesize both soluble and insoluble dextran which forms a complex and inhomogeneous polymer network. However, the traditional rheometer has a limitation to capture in situ properties of inherently porous and inhomogeneous biopolymers. Therefore, we used the particle tracking microrheology to characterize the material properties of the dextran polymer. TEM images revealed a range of pore size mostly less than $20{\mu}m$, showing large pores > $2{\mu}m$ and small pores within the solid matrix whose sizes are less than $1{\mu}m$. Microrheology data showed two distinct regimes in the bacterial dextran, purely viscous pore region of soluble dextran and viscoelastic region of the solid part of insoluble dextran matrix. Diffusive beads represented the soluble dextran dissolved in an aqueous phase, of which viscosity was three times higher than the growth medium viscosity. The local properties of the insoluble dextran were extracted from the results of the minimally moving beads embedded in the dextran matrix or trapped in small pores. At high frequency (${\omega}>0.2Hz$), the insoluble dextran showed the elastic behavior with the storage modulus of ~0.1 Pa. As frequency decreased, the insoluble dextran matrix exhibited the viscoelastic behavior with the decreasing storage modulus in the range of ${\sim}0.1-10^{-3}Pa$ and the increasing loss modulus in the range of ${\sim}10^{-4}-1\;Pa$. The obtained results provide a compilation of frequency-dependent rheological or viscoelastic properties of soft gel-like porous biopolymers at the particular conditions where soil bacteria produce bacterial biopolymers in subsurface.