• Proceedings of the Korean Geotechical Society Conference
• /
• 1989.10a
• /
• pp.1.1-10
• /
• 1989

본 연구에서는 유효응력 개념에 기초를 둔 응력-변형을 관계식을 이용하여 비배수 지하굴착 거등을 모댈하기 위한 수치해석적 방법이 개발된다. 비배수 조건 시 적용되는 체적불변형 조건은 조건방정식(Penalty formulation)의 혁태로 공극수압 변수를 이용하여 주어지며 결과되는 유한요소 방정식에 상닻히 른 물외 체적변형 개수를 부여함으로서 이루어진다. 이러한 형태와 조건식은 지하굴착 과정에서 발생되는 비배수 공극수압의 계산을 가능케 한다. 체적불변형 조건 부여 시 발생되는 mesh locking은 그 결과에 상당한 영향을 미치므로 이러한 mesh locking 문제는 T-방법에 근거를 둔 salective 적분방법월 적용함으로서 해결될 수 있다. 또한 흙의 거등을 모델하기 위하여 사용 된 Cam-Clay모텔과 Drucker-prager모텔에 새로운 implicit 웅력적분 방법을 적용함으로서 효율적인 방법으로 비선형거동을 해석할 수 있다. 개발된 지하 굴착 해석방법의 적용성을 검증하기 위하여 실재 현장에서 측정된 지하굴착 거동을 예제로 이용하였다.

• Journal of the Korean Geotechnical Society
• /
• v.17 no.5
• /
• pp.29-36
• /
• 2001

한반도 남해안의 광양만에서 채취한 연약 해성점토의 물리적 및 역학적 특성을 조사하기 위한 일련의 실내시험을 수행하였다. 물리적 성질 및 압밀시험 결과의 분석에 따르면, 시험에 사용된 시료는 정규압밀점토로 나타났다. 압밀비배수 삼축시험 결과로부터 새로운 간극수압계수(C)를 제안하였고, 이 계수는 유효응력경로를 예측하기 위한 방정식에 적용되었다. 또한, 비배수조건에서 전단변형률은 오로지 응력비만의 함수라는 사실이 실험결과로부터 밝혀졌다. 따라서 비배수 조건에서의 전단변형률 계산식이 제안되었으며, 이들 관계식을 이용하여 비배수(CIU) 및 배수조건(CID)에서의 점토의 거동을 예측하기 위한 새로운 구성방정식이 제안되었다. 이 구성방정식은 Roscoe와 Poorooshasb이 제안한 증분응력-변형률 이론을 기초로 하였으며, 제안된 구성방정식을 적용하여 예측한 배수전단특성을 실측된 결과에 매우 근접하는 경향을 나타내었다.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.7 no.3
• /
• pp.409-413
• /
• 2006

The accumulated deformation due to the undrained creep causes the general stability problem for the overall soil mass. In this study, the time-dependent constitutive equation, into which a damage law, modified cam clay model, and Perzyna's generalized viscous theory were incorporated, was derived microscopically. The model prediction agreed well with the experimental result including the case of the undrained creep rupture.

• Journal of the Korean Geotechnical Society
• /
• v.21 no.4
• /
• pp.31-40
• /
• 2005

This study proposed a new yield function considering the spacing ratio of the critical state to predict the undrained shear behavior of anisotropic field ground. We have suggested a nonassociated constitutive model that used a newly modified plastic potential function in order to apply the yield function of the modified Cam-Clay model to the anisotropic consolidation. In this paper, we predicted undrained shear behavior of the remolded weathered mudstone soils in Phohang isotorpically and anisotropically consolidated using the suggested model. To evaluate the reliability of proposed model, we predictied undrained shear behavior of Bankok Clay isotropically, nomally consolidated and Drammen Clay Ko consolidated. The predicted results are consistent with the observed behavior.

• Geotechnical Engineering
• /
• v.10 no.1
• /
• pp.7-18
• /
• 1994

A new model for describing the behavior of clay under monotonic and cyclic loading is proposed. This model uses the hyperbolic representation for the stress -strain relationship in overconsolidated state and it describes undrained effective stress path on the basis of the critical state theory. The developed constitutive model by using an energy dissipation equation can describe the behavior of clay in heavily overconsolidated state as u.ell as lightly overconsolidated state under monotonic loading. In order to extend the model for the behavior of clay under cyclic loading, a shift function of undrained stress spacing ratio is introduced in the constitutive model developed for monotonlc loading. A single additional parameter is required to represent the cyclic effect and it can be reasonably deter mined from the test results. The measured behavior in undrained cyclic triaxial tests has been easily and precisely predicted by the newly developed constitutive model.

• Geotechnical Engineering
• /
• v.5 no.4
• /
• pp.47-60
• /
• 1989

Soft offshore sediments quite frequently contain undissolved gas, probably methane pro- duced biogenically. The presence of gas bubbles can have a significant effect on the engineering behaviours of the seabed. One of the main difference between saturated and gassy soils is that the undrained response is not incompressible, and without volume change, may be assumed for a fully saturated soil. This paper describes the basic experimental work to further understanding of a gassy soil. The test has been performed for a gassy soil under undrained and drained conditions. It was confirmed that the gas inclusions deformed due to changes in the total stress on the sample and also the pore gas pressure response to change in total stress. but not directly to those in pore water pressure. And the test which applied the repeated load under undrained state also showed the similar behaviour as the simple load.

• Journal of the Korean Geotechnical Society
• /
• v.22 no.10
• /
• pp.151-163
• /
• 2006

This paper presents the interrelationship between undrained static and cyclic shear behavior. Laboratory works were performed through the undralned static and cyclic triaxial test using Nak-Dong River sand. And static triaxial test involved the triaxial extension test for comparison with cyclic shear behavior Cyclic triaxial test was performed with a variety of combination conditions of initial static shear stress $(q_{st})$ and cyclic stress $(q_{cy})$. In this result, the stress path of cyclic shear behavior was correspondent with static shear behavior passing the critical stress ratio (CSR) line because of the development of flow deformation. After that, a failure occurred according to failure line (FL) of static shear behavior. The stress path of cyclic shear behavior showed essentially the same with static shear behavior, although it appears a little different in test method.

• Journal of the Korean GEO-environmental Society
• /
• v.9 no.6
• /
• pp.61-70
• /
• 2008

In this study, undrained triaxial (CU) tests were performed on low-plastic silt of Nakdong River in order to investigate the undrained shear behavior of low-plastic silt. In experimental results, the deviator stress showed the hardening behavior after reaching its yield stress like the tendency of common sand, and the pore water pressure was gradually decreased to critical state after the maximum value. In the effective stress paths, regardless of consolidation stress or overconsolidation ratios, both a critical state line (CSL) and a phase transformation line (PTL) exist in the effective stress path that is similar to the case of sand. The behavior of low-plastic silt was predicted by the Modified Cam-Clay (MCC) model, the Jordan and the Elman-jordan model that is artificial neural network model. According to predicted results, the overall undrained shear behavior of low-plastic silt could not be predicted with the MCC model, but the Jordan and Elman-Jordan model showed well-matched experiment results.

• Journal of the Korean Geotechnical Society
• /
• v.21 no.8
• /
• pp.13-26
• /
• 2005

It was known that the aging effect of sands is insignificant in comparison with clays, and hence the study on this effect had seldom been performed prior to the early 1980s. However, field tests for this effect have been actively carried out since it was investigated that penetration resistance of reformed sands increased with the lapse of time. Recently, the aging effect of sands has also been examined in laboratory testings. In this study, undrained static triaxial tests were performed to evaluate the effect on the Nak-dong River sands, with different .elative densities $(D_r)$, consolidation stress ratios $(K_c)$, and consolidation times. As a result of the tests, it was proved that the undrained cyclic shear strength $(R_f)$ increased with the aged time on the sands. The in situ range of Rf on the sands, which is applicable to the magnitude of earthquake in the Nak-dong River area, was proposed by using the test results.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.5 no.5
• /
• pp.471-479
• /
• 2004

In this study, a time-dependent constitutive model was developed for cohesive soils. A damage law was included in the model, using which the undrained creep behavior was predicted. The mathematical and physical derivation of the model was performed in the sense of adopting only few model parameters. The model prediction was well agreed with the experimental result of creep testing including creep rupture.