• Journal of the Korean Geotechnical Society
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• v.19 no.5
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• pp.133-144
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• 2003

Horizontal consolidation characteristics of Busan marine clay were investigated by computing coefficient of horizontal consolidation from Piezocone data and comparing their results with those of standard consolidation test. It is well known that current prediction models of $c_h$ for high plastic soils have large uncertainties, and show a great difference between the predicted and the measured values. However, the spherical models and expanding cavity theory of Torstensson(1977), and Burns & Mayne(1998) based on modified Cam-Clay model with critical limit state concepts have relative reliability in estimating $c_h$ and good applicability in highly plasticity soils. In this paper, a normalization technique was used to evaluate $c_h$ using the Burns and Mayne's method based on the dissipation test, and their normalized consolidation curves give 0.015 of time factor($T_{50}$) when 50% degree of consolidation is completed. Comparison study using Piezocone data obtained at other similar ground site shows 1.5 times less systematicality than that of standard consolidation test, which indicates considerable approximation with the measured values because standard consolidation test gives the difference of three to few times compared with the measured values. In addition, design chart for estimating $c_h$ based on the chart from Robertson et al.(1992) and using the other method of the direct prediction from the of dissipation test was newly proposed. It is judged that new proposed chart is very applicable to Korean marine soils, especially in very high plastic soils.

• Journal of Industrial Technology
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• v.22 no.B
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• pp.211-218
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• 2002

The paper is to show the behavior of composit ground which is installed with sheet pile in soft soil improved by sand compaction pile. The results of load-settlement relationship, earth pressure, stress concentration characteristics, and final water content were obtained by centrifuge model test. Two cases of tests, installation of sheet pile on the corner and both side of the loading plate for the improved SCP ground which was designed twice of the footing width, were performed for the tests under the vertical and horizontal loading and both side of corner. Finite element program(CRISP) for sand compaction pile using elasto-plastic model and numerical analysis for soft soil using modified cam-clay constitutive equation were compared and analized with the results of model tests. The result of analysis show the increased bearing capacity of soil after, SCP and sheet pile was installed.

• Proceedings of the Korean Geotechical Society Conference
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• 1991.10a
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• pp.87-102
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• 1991

It has been reported that the failure of Carsington Dam in Eng1and occured due to the existence of a thin yellow clay layer which was not identified during the design work, and due to pre-existing shears of the clay layer. The slope stability analyses during the design work, which utilized traditional circular arc type failure method and neglected the existence of the clay layer, showed a safety factor of 1.4. However, the post-failure analyses which utilized translational failure mode considering the clay layer and the pre-existing shear deformation revealed the reduction of safety factor to unity. The post-failure analysis assumed 10。 inclination of the horizontal forces onto each slice based on the results of finite element analyses. In this paper, Bishop's simplified method, Janbu method, and Morgenstern-Price method were used for the comparison of both circular and translational failure analysis methods. The effects of the pre-existing shears and subsquent movement were also considered by varying the soil strength parameters and the pore pressure ratio according to the given soi1 parameters. The results showed factor of safefy 1.387 by Bishop's simplified method(STABL) which assumed circular arc failure surface and disregarding yellow clay layer and pre-failure material properties. Also the results showed factor of safety 1.093 by Janbu method(STABL) and 0.969 by Morgenstern-Price method(MALE) which assumed wedge failure surface and considerd yellow clay layer using post failure material properties. In addition, dam behavior was simulated by Cam-Clay model FEM program. The effects of pore pressure changes with loading and consolidation, and strength reduction near or at failure were also considered based on properly assumed stress-strain relationship and pore pressure characteristics. The results showed that the failure was initiated at the yellow clay layer and propagated through other zones by showing that stress and displacement were concentrated at the yel1ow clay layer.

• Geotechnical Engineering
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• v.12 no.5
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• pp.17-26
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• 1996

The undrained behavior of Asan marine soil was investigated by using an automated triaxial testing device. The stress-strain behavior at the preand postfailure state of marine soil under undrained compression and eatension conditions was compared with the behavior of pure silt, pure clay and the overall behavior of Asan marine soil was predicted with the modified Camflay model and the bounding surface model. The marine soil sampled in Asan bay area was clayey silts with 70oA silt-30% clay content and the testing samples were prepared in both undisturbed and remolded conditions. All samples are normally consolidated with 400 kPa of effective mean confining pressure and each sample is unloaded to 200, 100, 67 kPa, respectively. And then the shear test was performed with different confining pressure. According to experimental results, there exists an unique failure line whose slope is lower than silt's and higher than clay's. It is identified that the undrained shear strength of normally consolidated samples increases after crossing the phase transformation line because of volume dilation tendency which is not seen in clay. Overconsolidated samples show different soil behavior compared with pure silt due to its tendency of change in volume. It is also found that the overall behavior of Asan marine soil cannot be predicted precisely with the modified Cam-clay model and the bounding surface model.

• Tunnel and Underground Space
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• v.30 no.1
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• pp.39-62
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• 2020

In this study, Barcelona Basic Model (BBM) was implemented into TOUGH2-MP/FLAC3D for the numerical analysis of coupled thermo-hydro-mechanical (THM) behavior of unsaturated soils and the prediction of long-term behaviors. Similar to the methodology described in a previous study for the implementation of BBM into TOUGH-FLAC, the User Defined Model (UDM) of FLAC based on the Modified Cam Clay Model (MCCM) and the FISH function of FLAC3D were used to extend the existing MCCM module in FLAC3D for the implementation of BBM into TOUGH2-MP/FLAC3D. In the developed BBM module in TOUGH2-MP/FLAC3D, the plastic strains due to change in suction increase (SI) in addition to mean effective stress are calculated. In addition to loading-collapse (LC) yield surface, suction increase (SI) yield surface is changed by hardening rules in the developed BBM module. Several numerical simulations were conducted to verify and validate the implementation of BBM: using an example presented in the FLAC3D manual for the standard MCCM, simulation results using COMSOL, and experimental data presented in SKB Reports. In addition, the developed BBM analysis module was validated by simultaneously performing a series of modeling tests that were performed for the validation of the Quick tools developed for the purpose of effectively deriving BBM parameters, and by comparing the Quick tools and Code_Bright results reported in a previous study.

• Geomechanics and Engineering
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• v.29 no.1
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• pp.1-11
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• 2022

A semi-analytical solution to responses of overconsolidated (OC) unsaturated soils surrounding an expanding spherical cavity under constant suction condition is presented. To capture the elastoplastic hydro-mechanical property of OC unsaturated soils, the unified hardening (UH) model for OC unsaturated soil is adopted in corporation with a soil-water characteristic curve (SWCC) and two suction yield surfaces. Taking the specific volume, radial stress, tangential stress and degree of saturation as the four basic unknowns, the problem investigated is formulated by solving a set of first-order ordinary differential equations with the help of an auxiliary variable and an iterative algorithm. The present solution is validated by comparing with available solution based on the modified Cam Clay (MCC) model. Parametric studies reveal that the hydraulic and mechanical responses of spherical cavity expanding in unsaturated soils are not only coupled, but also affected by suction and overconsolidation ratio (OCR) significantly. More importantly, whether hydraulic yield will occur or not depends only on the initial relationship between suction yield stress and suction. The presented solution can be used for calibration of some insitu tests in OC unsaturated soil.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.10a
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• pp.312-333
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• 2006

This paper presents the results of an analysis of the excess porewater pressure distribution due to piezocone penetration in overconsolidated clays. From piezocone test results for moderately and heavily overconsolidated clays, it was observed that the excess porewater pressure increases monotonically from the piezocone surface to the outer boundary of the shear zone and then decreases logarithmically to the outer boundary of the plastic zone. It was also found that the size of the shear zone decreases from approximately 2.2 to 1.5 times the cone radius with increasing OCR, while the plastic radius is about 11 times the piezocone radius, regardless of the OCR. The equation developed in this study based on the modified Cam clay model and the cylindrical cavity expansion theory, which take into consideration the effects of the strain rate and stress anisotropy, provide a good prediction of the initial porewater pressure at the piezocone location. The method of predicting the spatial distribution of excess porewater pressure proposed in this study is based on a linearly increasing ${\Delta}u_{shear}$. In the shear zone and a logarithmically decreasing ${\Delta}u_{oct}$, and is verified by comparing with the excess porewater pressure measured in overconsolidated specimens at the calibration chamber.

• Geotechnical Engineering
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• v.11 no.3
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• pp.43-54
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• 1995

The aim of the work described in this paper is to develope a constitutive model for the prediction of an unsaturated soil and to confirm the application'of the model, which is composed of the elastic and plastic part in consideration of the matric suction and the net mean stress. From test results, volume changes and deviator stresses are analyzed at each state and their relationships are formulated. The application of the model to silty sands is confirmed by the comparison between test and predicted results. During drying -wetting and loading -unloading processes for isotropic states, the agreement between predicted and test results are satisfactory. Predicted deviator stresses are well agreed with test results in shearing process. Overall acceptable predictions are reproduced in high confining pressure. Usefulness of the model is confirmed for the unsaturated soil except volumetric strain, which is not well agreed with the test results due to deficiency of dilatancy of the model in low confining pressure. It is, therefore. recommended to study the behavior of dilatancy for an unsaturated soil.

• Geotechnical Engineering
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• v.12 no.6
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• pp.87-100
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• 1996

This paper verifies the accuracy and efficiency of the implicit stress integration algorithm for an anisotropic hardening constitutive model developed in a companion paper[Oh & Lee (1996)3. Simulation of undrained triaxial test results shows the accuracy of the method through an error estimation, and analyses of accuracy and convergence were performed for a numerical excavation problem. As a result, the stress was accurately integrated by the algorithm and the nonlinear solution was converged to be asymptotically quadratic. Furthermore nonlinear FE analysis of a real excavation problem was by performed considering the initial soil conditions and the in-situ construction sequences. The displacements of wall induced by excavation were more accurately estimated by the anisotropic hardening model than by the Cam-clay model.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.300-310
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• 2008

A series of numerical simulations on the several types of breakwaters on the foundation systems utilizing buoyancy were carried out in plane-strain conditions using the modified Cam-Clay model and the Biot's consolidation theory. Improved foundation system by the replacement of original ground with light weighted material, expandable poly-styrene (called below EPS) and several foundation systems with buoyant cells were used. From the results of numerical simulations we found that the foundation systems utilizing buoyancy are efficient to reduce the maximum consolidation settlements without reducing lateral safety.