• Journal of the Korean Geotechnical Society
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• v.16 no.2
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• pp.103-113
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• 2000

기존의 Terzaghi 압밀이론은 상대적으로 연약토층이 두껍지 않고, 초기함수비가 낮으며 적은 유효응력의 증가가 예상되는 곳에 그 적용이 제한되어 있었다. 그 이유는 Therzaghi 압미이론 자체가 미소변형률과 선형적인 압축성 및 투수성등을 기본적인 가정사항으로 내포하고 있기 때문이다. 이러한 가정사항을 극복하고자 Gibson et al. 은 일차원 비선형 유한 변형률 압밀이론에 관한 엄밀해를 제시하였다. 이 이론은 기존의 많은 가정사항들을 극복하여 실제 현상에 더욱 부합하는 예측을 할 수 있는 장점이 있는 반면, 비선형적인 응력-변형 관계, 변형-투수계수 관계의 도입과 좌표변환 및 현장의 시고이력을 그대로 적용하는데 많은 어려움이 있는 것이 사실이다. 본 연구에서는 이러한 비선형 유한형태를 압밀이론을 이용한 압밀현상 예측을 위하여, 비선형적인 응력-변형 관계, 변형-투수계수 관계에 관한 함수식을 구성하고 이를 포함하는 컴퓨터 프로그램을 개발하였다. 개발 프로그램은 많은 폼과 모듈로 구성되어 있는데, 이러한 각각의 폼과 모듈은 GUI 기능의 극대화를 통해 복잡한 이론에 익숙하지 않은 실무자들이 쉽게 본 이론을 이용할 수 있도록 설계 되었다. 또한 개발프로그램은 다양한 하중단계 및 비선형적인 응력-변형 관계, 변형-투수계수 관계에 관한 회귀분석, 각 유효응력 단계별 상이한 비선형 계수 g와 λ를 적용할 수 있으며, 계산을 위한 전처리과정은 물론 계산된 결과를 위한 다양한 후처리과정이 모두 사용자 위주의 GUI 기능을 충분히 갖도록 설계되었다. 개발 프로그램의 검증을 위하여 실제 현장의 계측자료 및 기존 연구문헌상의 결과와 본 개발 프로그램의 예측결과를 비교.분석하였으며, 다양한 간극비 상태의 비선형 계수가 해석결과에 미치는 영향을 알아보았다.

• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.73-84
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• 2005

A three layered neural network model was developed using back propagation algorithm to estimate the UU undrained shear strength of Korean soft soil based on the database of actual undrained shear strengths and piezocone measurements compiled from 8 sites over the Korea. The developed model was validated by comparing model predictions with measured values about new piezocone data, which were not previously employed during development of model. Performance of the neural network model was also compared with conventional empirical methods. It was found that the number of neuron in hidden layer is different for the different combination of transfer functions of neural network models. However, all piezocone neural network models are successful in inferring a complex relationship between piezocone measurements and the undrained shear strength of Korean soft soils, which give relatively high coefficients of determination ranging from 0.69 to 0.72. Since neural network model has been generalized by self-learning from database of piezocone measurements and undrained shear strength over the various sites, the developed neural network models give more precise and generally reliable undrained shear strengths than empirical approaches which still need site specific calibration.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.55-62
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• 2002

미소변형에서 대변형에 이르는 전체 변형률 영역의 구성모델을 ABAQUS 코드에 구현하였다. 구성모델은 비등방경화규칙에 근거한 전응력 개념의 탄소성 모델로 연약 점토나 풍화토에 적용하는 것이 가능하다. 사용된 정식화 및 알고리즘은 (1) Jaumann 응력속도를 이용한 대변형도 조건 정식화 (2) 내재적인 응력적분 (3) 일관된 접선계수를 포함하고 있다. 이를 통하여 대변형 해석을 정확하고 효율적으로 수행할 수 있었다. 예제를 통하여 새로운 구성모델과 ABAQUS 코드를 이용한 대변형 해석을 수행할 수 있음을 확인하였다. 특히 전체변형률 영역의 거동을 모델하고 범용 해석 프로그램을 이용한 비선형 대변형 해석에 적용하는 것이 가능하였다.

• Journal of the Earthquake Engineering Society of Korea
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• v.14 no.6
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• pp.67-74
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• 2010

Because of the difference between the actual and computed eccentricity of buildings, symmetrical buildings will be affected by torsion. In provisions, accidental eccentricity is intended to cover the effect of several factors, such as unfavorable distributions of dead- and live-load masses and the rotational component of ground motion about a vertical axis. The torsional amplification factor is introduced to reduce the vulnerability of torsionally imbalanced buildings. The effect of the torsional amplification factor is observed for a symmetric rectangular building with various aspect ratios, where the seismic-force-resisting elements are positioned at a variable distance from the geometrical center in each direction. For verifying the torsional amplification factor in provisions, nonlinear reinforced concrete models with various eccentricities and aspect ratios are used in rock. The difference between the maximum displacements of the flexible edge obtained between using nonlinear static and time-history analysis is very small but the difference between the maximum torsional angles is large.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.215-228
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• 2002

In a companion paper. (Oh, 2002), the constitutive model, called GUX model, was implemented as a user subroutine in ABAQUS code, where the GUX model could describe the behavior of overall strain range. An accuracy analysis verified that the implicit stress integration maintained the accuracy of solutions successfully. Since the GUX model is an anistropic hardening elasto-plastic constitutive model based on total stress concept, geotechnical problems under fully drained or undrained condition can be analyzed after acquisition of stress-strain relationships from drained or undrained triaxial tests. This study includes the analyses of the stability of embankments on soft clays and weathered soils and the example of axially loaded soil-pile system. In the large deformation analyses, geometric nonlinearity was considered and the result of analyses with GUX model was compared with that of Mises model for the overall strain range behavior.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.1348-1353
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• 2006

In this paper, nonlinear elasto-plastic analysis was performed to investigate the stability of the rapid embankment under undrained condition. The commercial code ABAQUS/Standard was used in the study. Resonant Column test (RC test) results and Ramberg-Osgood model were utilized to simulate the nonlinear behavior of soft clay. Ramgerg-Osgood model was tested whether it simulates the nonlinear behavior of the soil properly in first. Then the analysis result was compared with the previous research results. It was found that the Ramberg-Osgood model matched well with the soil behavior of soft clay in the rapid embankment under undrained condition.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.17 no.2
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• pp.98-105
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• 2005

A new type breakwater is developed for small scale harbors and fishing ports with low design wave and soft ground. The structure of the developed breakwater is similar to the soldier pile used in soil excavation. Structural performance of the new type breakwater can not be accurately evaluated by numerical analysis due to nonlinearity of joints between piles and honelasticity of soil support. Therefore, this paper investigates the structural performance of the breakwater with experimental method and compares the results with numerical analysis.

• Journal of the Korean Geosynthetics Society
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• v.13 no.4
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• pp.97-107
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• 2014

Finite element modelling and analysis were conducted for the roll-type steel mats which were placed on loose sand and subjected to a standard truck wheel load in this study. The roll-type steel mats mean that the steel mats can be folded as a circle shape for the carrying to fields in cold regions where workability is limited and are developed for a rapid rehabilitation method for roadway across soft ground which is caused by thawing during the summer season in cold regions. The model is composed of link elements to simulate nonlinear behavior of connections between steel mats, thick shell elements to have flexural stiffness of the steel mats, and springs to simulate characteristics of foundation soils. The structural behaviors of the shell, link elements, and springs were verified at each modelling step through experiment and analysis. Beam and shell analysis without the link elements were conducted and compared to results obtained from the model presented in this study. Significant vertical displacement is shown in the shell model with hinge connections. Therefore, the results demonstrate that the analysis model for the roll-type steel mats on loose sand needs further detail parametric studies.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.77-87
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• 2004

In this paper a back-propagation neural network model is developed to estimate the preconsolidation pressure of Korean soft soils based on 176 oedometer tests and 63 piezocone test results, which were compiled from 11 sites - western and southern parts of Korea. Only 147 data were used for the training of the neural network and 29 data, which were not used during the training phase, were used for the verification of trained network. Empirical and theoretical models were compared with the developed neural network model. A simple 4-4-9-1 multi-layered neural network has been developed. The cone tip resistance $q_T$ penetration pore pressure $u_2$, total overburden pressure $\sigma_{vo}$ and effective overburden pressure $\sigma'_{vo}$ were selected as input variables. The developed neural network model was validated by comparing the prediction results of the proposed neural network model for the new data which were not used for the training of the model with the measured preconsolidation pressures. It can also predict more precise and reliable preconsolidation pressures than the analytical and empirical model. Furthermore, it can be carefully concluded that neural network model can be used as a generalized model for prediction of preconsolidation pressure throughout Korea since developed model shows good performance for the new data which were not used in both training and testing data.

• Journal of the Korean Geotechnical Society
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• v.15 no.6
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• pp.131-142
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• 1999

The objective of this study is to perform finite element analyses using the anisotropic hardening constitutive model on the basis of the total stress concept. An anisotropic hardening constitutive model had been developed in a companion paper, and was then formulated by implicit stress integration and consistent tangent moduli. A nonlinear finite element analysis program was coded including the algorithm, and as a result, the nonlinear solution was accurately calculated and converged to be asymptotically quadratic. In the analysis of a test embankment it was found that the proposed model could predict the displacement of soils more reasonably than the analysis with von Mises type model. In addition the proposed model could predict accurately the actual behavior through the reanalysis of the problem by a reasonable evaluation of the strength parameter.