• 한국지반공학회지:지반
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• 제1권1호
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• pp.59-72
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• 1985

본 논문은 Biot의 압밀이론을 유한요소법에 의해 해석하는 데 있어 수정 Cam-clay model과 해석 기법으로서는 Christian Boehmer방법을 사용한 것이다. 특히 본 해석에 있어서 압밀의 시간간격과 요소의 분할은 정도와 경제성의 관점에서 연구하였다. 나아가 본 프르그램의 정확을 조사하기 인하여 본 프로그램에 Terzaghi의 정해에 의한 일차원추밀의 해석을 시도하여 그 정상성을 확인하고 또한 Magnan이 연구목적으로 수행한 프랑스의 Cubzac-les-ponts에서 시험성토의 결과와 비교하였다. 본 연구에서 얻은 주요결론은 다음과 같다. 1. 일차원압밀의 평우에 배수층에 가까이 갈수록 요소를 세분하면 수치해석에서 더 높은 결과를 얻을 수 있다. 2. 상간간격에 대해서는 1 log cycle당 20회로 하면 안정된다. 3. 긴 배수거리를 갖는 요소에서는 Mandel-cryer 효과가 시간지연과 더불어 일어난다. 4. 본 프로그램에 의해 예측된 초기하중 단계에서 축변위는 성토하중으로 산하는 것 보다도 강성을 주는 Mesh화한 것이 관측치와 잘 일치한다. 5. 본 프로그램에 의해 예측된 간극수압은 Magnan결과와 비교해 볼 때 관측치와 더 잘 일치 한다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2000년도 춘계학술대회논문집
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• pp.606-611
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• 2000

It has been noted that the low frequency absorption coefficient of a porous sample placed in a standing wave tube is affected by the nature of the sample's edge constraint. The edge constraint has the effect of stiffening the solid phase of the sample, which itself can be strongly coupled to the material's fluid phase, and hence the incident sound field, by viscous means at low frequencies. In recent work it has also been shown that such a circumferential constraint causes the low frequency transmission loss of a layer of fibrous material to approach a finite low frequency limit that is proportional to the flow resistance of the layer and which is substantially higher than that of an unconstrained sample of the same material. However, it was also found that the benefit of the circumferential edge constraint was reduced in a transitional frequency range by a shearing resonance of the sample. Here it will be shown that the effect of that resonance can be mitigated or eliminated by adding additional axial and radial constraints running through the sample. It will also be shown that the constraint effect can be modeled closely by using a finite element procedure based on the Biot poroelastic theory. Implications for low frequency barrier design are also discussed.

• Geomechanics and Engineering
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• 제23권4호
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• pp.327-338
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• 2020

The role of precise prediction of subsurface fluids and discrimination among them cannot be ignored in reservoir characterization and petroleum prospecting. A suitable rock physics model should be build for the extraction of valuable information form seismic data. The main intent of current work is to present a rock physics model to analyze the characteristics of seismic wave propagating through a cracked porous rock saturated by a three phase fluid. Furthermore, the influence on wave characteristics due to variation in saturation of water, oil and gas were also analyzed for oil and water as wet cases. With this approach the objective to explore wave attenuation and dispersion due to wave induce fluid flow (WIFF) at seismic and sub-seismic frequencies can be precisely achieved. We accomplished our proposed approach by using BISQ equations and by applying appropriate boundary conditions to incorporate heterogeneity due to saturation of three immiscible fluids forming a layered system. To authenticate the proposed methodology, we compared our results with White's mesoscopic theory and with the results obtained by using Biot's poroelastic relations. The outcomes reveals that, at low frequencies seismic wave characteristics are in good agreement with White's mesoscopic theory, however a slight increase in attenuation at seismic frequencies is because of the squirt flow. Moreover, our work crop up as a practical tool for the development of rock physical theories with the intention to identify and estimate properties of different fluids from seismic data.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.728-733
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• 2008

Though multi-panel structures lined with a poroelastic material have been widely used to reduce sound transmission in various fields, most of the previous works to design them were conducted by repeated analyses or experiments based on initially given configurations or sequences. Therefore, it was difficult to obtain the optimal sequence of multi-panel structures lined with a poroelastic material yielding superior sound isolation capability. In this work, we propose a new design method to sequence a multi-panel structure lined with a poroelastic material having maximized sound transmission loss. Being formulated as a one-dimensional topology optimization problem for a given target frequency, the optimal sequencing of panel-poroelastic layers is systematically carried out in an iterative manner. In this method, a panel layer is expressed as a limiting case of a poroelastic layer to facilitate the optimization process. This means that main material properties of a poroelastic material are treated as Interpolated functions of design variables. The designed sequences of panel-poroelastic layers were shown to be significantly affected by the target frequencies; more panel layers were used at higher target frequencies. The sound transmission loss of the system was calculated by the transfer matrix derived from Biot's theory.

• Coupled systems mechanics
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• 제2권4호
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• pp.375-387
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• 2013

Soils consist of an assemblage of particles with different sizes and shapes which form a skeleton whose voids are filled with water and air. Hence, soil behaviour must be analyzed by incorporating the effects of the transient flow of the pore-fluid through the voids, and therefore requires a two-phase continuum formulation for saturated porous media. The present paper presents briefly the Biot's basic theory of dynamics of saturated porous media with u-P formulation to determine the responses of pore fluid and soil skeleton during cyclic loading. Kelvin elements are attached to transmitting boundary. The Pastor-Zienkiewicz-Chan model has been used to describe the inelastic behavior of soils under isotropic cyclic loadings. Newmark-Beta method is employed to discretize the time domain. The response of fluid-saturated porous media which are subjected to time dependent loads has been simulated numerically to predict the liquefaction potential of a semi-infinite saturated sandy layer using finite-infinite elements. A settlement of 17.1 cm is observed at top surface. It is also noticed that liquefaction occurs at shallow depth. The mathematical advantage of the coupled finite element analysis is that the excess pore pressure and displacement can be evaluated simultaneously without using any empirical relationship.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집A
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• pp.591-595
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• 2000

Sound absorbing characteristics of poroelastic materials is known to be greatly affected by high intensity acoustic waves. However, this effect has not been considered yet. In this study, the extended semilinear model based on Biot's theory for the porous materials and the characteristics of nonlinear waves in poroelastic sound absorbing materials were introduced. The expressions for the finite-amplitude acoustic plane waves were presented. By combining each nonlinear wave with appropriate matching conditions, we could investigate the effects of finite-amplitude acoustic waves on absorption characteristics of poroelastic materials. In the most ideal case considered in this paper, the absorption coefficient was found to become larger than that of linear incident waves. It was shown that the absorption coefficient became greater especially as frequency goes higher and as distance from the source goes larger. These phenomena may be inferred to result from 'dissipation effects due to nonlinearity'. This finding may have important implications for high intensity noise control.

• 한국소음진동공학회논문집
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• 제18권12호
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• pp.1262-1269
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• 2008

Though multilayered foam-panel structures have been widely used to reduce sound transmission in various fields, most of the previous works to design them were conducted by repeated analyses or experiments based on initially given configurations or sequences. Therefore, it was difficult to obtain an optimal sequence of multilayered foam-panel structure yielding superior sound isolation capability. In this work, we propose a new design method to sequence a multi-panel structure lined with a poroelastic material having maximized sound transmission loss. Being formulated as a one-dimensional topology optimization problem fur a given target frequency, the optimal sequencing of panel-poroelastic layers is systematically carried out in an iterative manner. In this method, a panel layer is expressed as a limiting case of a poroelastic layer to facilitate the optimization process. This means that main material properties of a poroelastic material are treated as interpolated functions of design variable. The designed sequences of panel-poroelastic multilayer were shown to be significantly affected by the target frequencies; more panels were obtained at higher target frequency. The sound transmission loss of the system was calculated by the transfer matrix derived from Biot's theory.

• Geomechanics and Engineering
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• 제21권3호
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• pp.279-288
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• 2020

The permeation grouting is a commonly used technique to improve the engineering geology condition of the soft ground. It is of great significance to predict the permeation range of the grout so as to ensure the effects of grouting. This paper conducts a theoretical analysis of jet-grouting effects in ground improvement and rotary grouting pile installation by utilizing deformation-permeation coupled poroelastic solutions based on Biot's theory and Laplace-Fourier integral transform technique. The exponential function and the intermittent trigonometric function are chosen to represent time-dependent grouting pressure usually encountered in ground improvement and rotary grouting pile installation process, respectively. The results, including the radial displacement, the hoop stress, the excess pore fluid pressure, the radial discharge, and the permeation radius of grout, are presented for different grouting time, radial positions and grouting lengths. Parametric study is conducted to explore the effects of variation of the exponent in the exponential grouting pressure-time relationship on grouting-induced responses. It is expected that the proposed solutions can be used to estimate the permeation range of grouting in ground improvement and rotary grouting pile installation.

• 한국지반공학회논문집
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• 제31권6호
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• pp.27-44
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• 2015

일정수심상에서 임의반사율을 갖는 부분중복파와 흐름이 공존하는 경우 얕은 두께를 포함한 유한두께 및 무한두께의 해저지반내에서 동적응답을 나타내는 해석해를 유도한다. 해석해에서 반사율이 0인 경우는 진행파와 흐름과의 공존장으로, 반사율이 1인 경우는 완전중복파와 흐름과의 공존장으로 간단히 변환된다. Biot의 압밀이론에 기초하여 해저지반은 투과탄성매체로, 간극유체는 압축성으로, 그리고 지반내 간극수의 흐름은 Darcy법칙으로 각각 가정된다. 도출된 해석해는 기존의 해석결과와의 비교 검토로부터 검증되며, 실제 계산에서는 반사율, 흐름속도, 입사파의 주기 및 지반두께 등의 변화에 따른 지반변위, 간극수압, 유효응력 및 전단응력의 변동특성을 면밀히 검토한다. 이로부터 흐름이 존재하는 경우 흐름으로 인한 입사파와 반사파의 주기 및 파장의 변화로 인하여 흐름이 없는 경우의 지반내 동적응답과는 큰 차이를 나타내며, 또한 반사율의 크기에 따라 동적응답에서 큰 차이가 나타난다는 것을 확인할 수 있다.

• Geomechanics and Engineering
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• 제18권1호
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• pp.11-20
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• 2019

The purpose of this study was to propose a new approach for quantifying in situ rock mass damage, which would include a degree-of-damage and the degraded strength of a rock mass, along with its prediction based on real-time Acoustic Emission (AE) observations. The basic approach for quantifying in-situ rock mass damage is to derive the normalized value of measured AE energy with the maximum AE energy, called the degree-of-damage in this study. With regard to estimation of the AE energy, an AE crack source location algorithm of the Wigner-Ville Distribution combined with Biot's wave dispersion model, was applied for more reliable AE crack source localization in a rock mass. In situ AE wave attenuation was also taken into account for AE energy correction in accordance with the propagation distance of an AE wave. To infer the maximum AE energy, fractal theory was used for scale-independent AE energy estimation. In addition, the Weibull model was also applied to determine statistically the AE crack size under a jointed rock mass. Subsequently, the proposed methodology was calibrated using an in situ test carried out in the Underground Research Tunnel at the Korea Atomic Energy Research Institute. This was done under a condition of controlled incremental cyclic loading, which had been performed as part of a preceding study. It was found that the inferred degree-of-damage agreed quite well with the results from the in situ test. The methodology proposed in this study can be regarded as a reasonable approach for quantifying rock mass damage.