• Journal of the Korean Geotechnical Society
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• v.29 no.12
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• pp.77-85
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• 2013

Unsaturated slopes experience infiltration during rainfall and become unstable when saturated. On the viewpoint of unsaturated effective stress, as matric suction decreases, both effective stress and shear strength decrease, which declines slope stability consequently. This study is focused on describing effective stress based on suction stress. The actual slope failures are simulated to calculate factors of safety in the field of finite element stress. In the residual soils of Hadong and Pohang, unsaturated properties are evaluated by laboratory tests. For unsaturated slopes, analyses of infiltration, stress and stability were performed to simulate actual failures. Based on unsaturated effective stress principle, the stability of actual slopes could be evaluated successfully. It is verified for the effective stress concept to be applicable to the engineering practice on slope design which considers infiltration by rainfall.

• Geotechnical Engineering
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• v.2 no.1
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• pp.55-66
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• 1986

Considering the effects of confining pressure, initial shear stress, cyclic stress ratio and number of loading cycles, cyclic triaxial tests are carried out to clarify the soil dynamic properties such as shear modulus and value of material damping of clay under undrained cyclic loading conditions. The results show that no obvious dependency on initial shear stress and effective confining stress are recognized in the shear modulus and damping ratio plotted versus strain. However, the shear modulus decreases and the damping ratio increases with increasing axial strain. When compared with others, it is also revealed that the shear moduli are distributed within the range curves obtained using empirical equations derived by Marcuson et al. (3) and Kokusho et al. (4), and damping ratios are distributed between the curves obtained by Kokusho et al. (4) and Ishihara et al. (9).

• Journal of the Korean Geotechnical Society
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• v.16 no.3
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• pp.29-37
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• 2000

많은 경우 액성한계 이상의 함수비 상태를 각즌 지반을 액체상태로 표현한다. 액체상태의 공학적 의미는 유효응력이 존재하지 않은 상태로 볼 수 있으며, 전단강도가 0임을 의미한다. 그러나 실제로는 액성한계 이상의 함수비를 갖는 지반에서도 유효응력이 존재하며, 따라서 전단강도가 존재한다. 연약한 해성점토의 경우는 이러한 경우가 비교적 흔하다. 일반적으로 액체상태란 용어에서 연상되는 지반상태는 물과 같은 상태로서 기술자로 하여금 지반의 상태에 대한 올바른 감을 가지는 것을 어렵게 한다. 본 고는 Bolt 의 electrical double layer 이론을 이용한 이론적 해석 및 실험적 자료들을 이용하여 액성한계란 용어의 올바른 제조명에 초점을 맞추었다.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.503-510
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• 2013

Shear wave velocity is widely used as an parameter for investigating subsurface characteristics and for obtaining the design parameters based on theoretical equations. This study seeks to estimate the coefficient of shear wave velocity in Busan clay via laboratory tests. Eight specimens were extracted at depths of 10, 12, 15, 20, 22, 25, 30, and 31 m. The specimens were subjected to the consolidation test to determine the relationship between effective stress and shear wave velocity. The relationship shows a non-linear trend and is similar to the results of a previous study. The coefficient shows constant coverage and a relationship between ${\alpha}$ and ${\beta}$ is suggested. The results demonstrate that this coefficient could be used as a reference value to determine engineering parameters based on the shear wave velocity.

• Journal of the Korean Geotechnical Society
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• v.36 no.12
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• pp.117-124
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• 2020

The present research focuses on a methodology to describe shearing response of clay with respect to temperature. An increase of temperature shifts the normal consolidation line to move down in the plane of void ratio and mean effective stress. The critical state line, however, does not move as much as the normal consolidation line in accordance with temperature increase. As temperature increase, therefore, the difference between the critical state mean effective stress and the pre-consolidation pressure reduces. To reflect this easily, the present study applies a bounding surface consisting of two parts divided by the critical state mean effective stress. This study calibrated a bounding surface for the soft Bangkok clay and performed elemental simulation for undrained triaxial compression tests. The elemental simulation showed that the model can describe the mechanical response upon temperature of clay without complex hardening and evolution rules compared to the experimental data.

• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.27-35
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• 2005

Several damages due to large displacement caused by liquefaction have been reported increasingly. Numerical procedures based on effective stress analysis are therefore necessary to predict liquefaction-induced deformation. In this paper, the fully coupled effective stress model called UBCSAND is proposed to simulate pore pressure rise due to earthquake or repeated loadings. The proposed model is a modification of the simple perfect elasto-plactic Mohr-Coulomb model, and can simulate a continuous yielding by mobilizing friction and dilation angles below failure state. Yield function is defined as the ratio of shear stress to mean normal stress. It is radial lines on stress space and has the same shape of Mohr-Columob failure envelope. Plastic hardening is based on an isotropic and kinematic hardening rule. The proposed model always causes plastic deformation during loading and reloading but it predicts elastic unloading. It is verified by capturing direct simple shear tests on loose Fraser River sand.

• Journal of the Korean Geotechnical Society
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• v.36 no.4
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• pp.5-15
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• 2020

This paper proposes a revised Modified Cam Clay type failure surface based on the critical state theory. In the plane of the mean effective and von Mises stresses, the original Modified Cam Clay model has an elliptic failure surface which leads the critical-state mean effective stress to be always half of the pre-consolidation mean effective stress without hardening and evolution rules. This feature does not agree with the real mechanical response of clay. In this study, the preconsolidation mean effective stress only reflects the consolidation history of the clay whereas the critical state mean effective stress only relies on the currenct void ratio of clay. Therefore, the proposed failure surface has a distorted elliptic shape without any fixed ratio between the preconsolidation and critical state mean effective stresses. Numerical simulations for various clays using failure surfaces as yield surface provide mechanical responses similar to the experimental data.

• Journal of the Korean GEO-environmental Society
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• v.17 no.7
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• pp.15-25
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• 2016

In the present work, a number of advanced three-dimensional (3D) parametric finite element numerical analyses have been conducted to study the behaviour of single piles and pile groups in consolidating ground from coupled consolidation analyses. Single piles, $4{\times}4$ and $6{\times}6$ piles inside groups with a spacing of 2.5D were considered, where D is the pile diameter. It has been found that dragload and downdrag on the piles developed rather quickly at the early stage of consolidation. However, when the degree of consolidation was more than 50~75%, only little increases of dragload and downdrag were induced on the pile. Negative Skin Friction (NSF) on the pile in the fill layer was mobilised quickly and remained constant throughout further consolidation. The development of NSF is influenced both by the relative shear displacements at the pile-soil interface and the vertical effective soil stresses during consolidation. The former governed the early stage of consolidation and the latter affected the later stage of consolidation. The vertical effective soil stresses adjacent to the piles were reduced due to the shear stress transfer at the pile-soil interface, in particular for piles inside the pile groups. The range of NSF influence zone concerning the reductions of the effective vertical soil stresses was about 20D measured from the piles in the horizontal direction. On the contrary, the effective horizontal soil stresses acting on the piles were similar to those at the far field.

• Journal of the Korean Geotechnical Society
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• v.28 no.3
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• pp.15-23
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• 2012

An internal friction angle, which is one of strength parameters of granular soils, can be obtained from direct shear tests or triaxial tests. The result of traixial tests can be influenced by various experimental conditions such as confining pressure, shearing rate, specimen diameter and height, and end constraint. In this study, undrained and drained shearing behaviors of Nakdong River sand were investigated for loose (Dr = 40%) and dense (Dr = 80%) specimens with 5, 7, and 10 cm in diameter. Friction angles such as undrained total stress friction angle, undrained effective stress friction angle, and drained friction angle obtained from Mohr's stress circle slightly increased and then decreased as a diameter of a specimen increased from 5, 7 to 10 cm, regardless of relative densities. The difference between friction angles caused by different specimen size was at maximum 4.5 degrees for undrained total stress friction angle of dense specimen. In most cases, there was little difference between friction angles of large and small specimens, which was less than 2 degrees. The difference between an effective friction angle from undrained tests and a drained friction angle from drained tests was at maximum 7 degrees for loose samples but negligible for dense samples.

• The Journal of Engineering Geology
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• v.23 no.4
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• pp.511-517
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• 2013

The Field Velocity Probe (FVP) has been widely applied to determine the various characteristics of soils. This study seeks to estimate soil consolidation characteristics using an FVP and to increase its application in the field. The specimens were extracted from depths of 3 and 6 m at the study site, an area of soft clay in Incheon. In laboratory testing, the specimens were placed in an improved oedometer cell to measure shear wave velocity, and statistical analysis was performed to compare the results of effective stress and shear wave velocity. FVP enables increased resolution in the field because it measures the shear wave velocity every 20 cm. To estimate the condition of consolidation, we compared the results of shear wave velocities between those obtained in the laboratory and those in the field. The field conditions are used to analyze overconsolidated and normally consolidated soils at depths of 3 and 6 m, respectively. The results show that FVP is a suitable method for estimating the degree of consolidation.