• Journal of the Korean Geotechnical Society
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• v.22 no.4
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• pp.61-71
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• 2006

A numerical procedure is presented fur evaluating seismic liquefaction on sloping ground sites. The procedure uses a fully coupled dynamic effective stress analysis with a plastic constitutive model called UBCSAND. The model was first calibrated against laboratory element behavior. This involved cyclic simple shear tests performed on loose sand with and without initial static shear stress. The numerical procedure is then verified by predicting a centrifuge test with a slope performed on loose Fraser River sand. The predicted excess pore pressures, accelerations and displacements are compared with the measurements. The results are shown to be in good agreement. The shear stress reversal patterns depend on static and cyclic shear stress levels and are shown to play a key role in evaluating liquefaction response in sloping ground sites. The sand near the slope has low effective confining stress and dilates more. When no stress reversals occur, the sand behaves in a stiffer manner that curtails the accumulated downslope displacements. The numerical procedure using UBCSAND can serve as a guide for design of new soil structures or retrofit of existing ones.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.1
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• pp.1-11
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• 2017

Seismic risk analysis was performed based on the total stress and effective stress of caisson type quay wall and pier type quay wall. In order to consider the effective stress effect, the pore pressure of the ground was distributed, using Byrne(1991) simple formula to estimate parameter and applied to the finn model. Through the results of seismic risk analysis according to the total stress and effective stress analysis method, the necessity of effective stress analysis in the seismic design of the quay wall installed on the soft ground was confirmed.

• Proceedings of the Korea Concrete Institute Conference
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• 1996.10a
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• pp.433-439
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• 1996

본 논문에서는 스트럿-타이 모델을 이용한 콘크리트 구조물의 설계 및 해석과정에서 필요로 하는 스트럿 유효강도의 결정 및 절점영역 지지력의 검토를 일반적이고 일관성 있게 수행할 수 있는 방법을 제안하였다. 콘크리트 스트럿의 유효강도는 스트럿-타이 모델의 스트럿 영역에 해당되는 유한요소들의 주응력비를 고려하여 결정하였으며, 스트럿의 기하하적인 형상을 이용하여 형성된 절점영역의 지지력은 조합응력을 받는 콘크리트의 파괴기준을 고려하는 비선형 유한요소 해석을 이용하여 검토하였다. 제안한 방법을 예증하기 위해 실험된 철근콘크리트 보의 해석을 스트럿-타이 모델 방법을 이용하여 실시하였다.

• Journal of the Korean Geotechnical Society
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• v.27 no.11
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• pp.55-69
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• 2011

The importance of unsaturated state in various geo-engineering problems has led to the advance of mechanical constitutive model emulating behavior of unsaturated soils in response to thermo-hydro-mechanical loading. Elasto-plastic mechanical constitutive model for unsaturated soil is formulated based on Bishop's effective stress. Effective stress and temperature are main variables in constitutive equation, and incremental formulation of constitutive relationship is derived to compute stress update and stiffness tensor. Numerical simulations involving coupled THM processes are conducted to discuss numerical stability and applicability of developed constitutive model: one-dimensional test, tri-axial compression test, and clay-buffering at high level radioactive waste disposal. Numerical results demonstrated that developed model can predict very complex behavior of coupled THM phenomena and is applicable to geo-engineering problems under various environmental conditions, as well as interpret typical behavior of unsaturated soils.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2C
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• pp.83-94
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• 2008

In this study an effective stress analysis was performed to evaluate liquefaction potential and ground settlement for reclaimed sites. The effective stress model can simulate the stiffness degradation due to excess pore pressure and resulting ground deformation. It is applicable to a wide range of strain. An equivalent linear analysis suitable for low strain levels was also carried out to compare the effective stress analysis. Shear stress ratio calculated from an equivalent linear analysis was used to determine SPT blow count to prevent liquefaction. Depending on the magnitude of potential earthquake and fine contents, the SPT blow count was converted into an equivalent cone tip resistance. It was compared with the measured cone tip resistance. The measured elastic shear wave velocity and cone tip resistance from two reclaimed sites in Incheon were used to perform liquefaction analyses. Two liquefaction evaluation methods showed similar liquefaction potential which was evaluated continuously. The predicted excess pore pressure ratio of upper 20 m was between 40% and 70%. The calculated post-shaking settlement caused by excess pore pressure dissipation was less than 10 cm.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.268-276
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• 2001

A numerical model for the thermal response analysis of concrete structures is suggested. The model includes the stress-strain relationship, constitutive relationship, and multiaxial failure criteria at elevated temperature conditions. Modified Saenz's model was used to describe the stress-strain relationship at high temperatures. Concrete subjected to elevated temperatures undergoes rapid strain increase and dimensional instability. In order to explain those changes in mechanical properties, a constitutive model of concrete subjected to elevated temperature is proposed. The model consists of four strain components; free thermal creep strain, stress-induced (mechanical) strain, thermal creep strain, and transient strain due to moisture effects. The failure model employs modified Drucker-Prager model in order to describe the temperature dependent multiaxial failure criteria. Some numerical analyses are performed and compared with the experimental results to verify the proposed model. According to the comparison, the suggested material model gives reliable analytical results.

• Journal of the Korean GEO-environmental Society
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• v.7 no.6
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• pp.133-143
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• 2006

A fully coupled effective stress dynamic analysis procedure for modeling seismic liquefaction on slope is presented. An elasto-plastic formulation is used for the constitutive model UBCSAND in which the yield loci are radial lines of constant stress ratio and the flow rule is non-associated. This is incorporated into the 2D version of Fast Lagrangian Analysis of Continua (FLAC) by modifying the existing Mohr-Coulomb model. This numerical procedure is used to simulate centrifuge test data from the Rensselaer Polytechnic Institute (RPI). UBCSAND is first calibrated to cyclic direct simple shear tests performed on Nevada sand. Both pre- and post-liquefaction behaviour is captured. The centrifuge test is then modeled and the predicted accelerations, excess porewater pressures, and displacements are compared with the measurements. The results are shown to be in general agreement. The procedure is currently being used in the design of liquefaction remediation measures for a number of dam, bridge, tunnel, and pipeline projects in Western Canada.

• Journal of the Korean Geotechnical Society
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• v.22 no.12
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• pp.89-98
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• 2006

In this paper the behavior of saturated sand deposits where liquefaction occurred before is studied for successive earthquakes. The relationship between past pore pressure generation and reliquefaction resistance is examined by using cyclic direct simple shear tests. If the soil sample in direct simple shear produced nearly 90% of excess pore pressure during first time loading, its liquefaction resistance increased during following cyclic loading after consolidation. However, a fully liquefied soil during first time loading has a densely packed condition but shows less liquefaction resistance for the following cyclic loading. UBCSAND model that can account for pore pressure change and stiffness loss of soil during shaking is used to analyze the centrifuge test simulating reliquefaction. The pore pressure rise during first time cyclic loading controls liquefaction resistance. The measurements from reliquefaction centrifuge test are compared with numerical predictions. By considering frequent earthquakes having occurred at the Southern Korea near Japan, such effective stress approach is necessary for reliquefaction study.

• The Journal of Engineering Geology
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• v.33 no.1
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• pp.151-167
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• 2023

This study compares the revised method in loose saturated sandy ground where the LNG storage tank will be installed with an evaluation method by one-dimensional effective stress analysis using the UBC3D-PLM model. Various laboratory and field tests were conducted to establish the parameters necessary for evaluation. The revised liquefaction evaluation method using the seismic response analysis result and N value from standard penetration testing evaluated the possibility of liquefaction as high, but assessment using effective stress analysis, which can consider various liquefaction resistance factors, found the site to be somewhat stable against liquefaction. One-dimensional finite element analysis using UBC3D-PLM modeling facilitated easier assessment of stability against liquefaction than the other methods and minimized the area required for reinforcement against liquefaction. In addition, it is expected that two-and three-dimensional numerical analysis considering the foundation of the LNG storage tank can identify the seismic design and behavior when liquefaction occurs.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.167-176
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• 2016

Shear friction strength model of concrete was proposed to explain the direct friction mechanism at the concrete interfaces intersecting two structural elements. The model was derived from a mechanism analysis based on the upper-bound theorem of concrete plasticity considering the effect of transverse reinforcement and applied axial loads on the shear strength at concrete interfaces. Concrete was modelled as a rigid-perfectly plastic material obeying modified Coulomb failure criteria. To allow the influence of concrete type and maximum aggregate size on the effectiveness strength of concrete, the stress-strain models proposed by Yang et al. and Hordijk were employed in compression and tension, respectively. From the conversion of these stress-strain models into rigidly perfect materials, the effectiveness factor for compression, ratio of effective tensile strength to compressive strength and angle of concrete friction were then mathematically generalized. The proposed shear friction strength model was compared with 91 push-off specimens compiled from the available literature. Unlike the existing equations or code equations, the proposed model possessed an application of diversity against various parameters. As a result, the mean and standard deviation of the ratios between experiments and predictions using the present model are 0.95 and 0.15, respectively, indicating a better accuracy and less variation than the other equations, regardless of concrete type, the amount of transverse reinforcement, and the magnitude of applied axial stresses.