• Journal of the Korean Geotechnical Society
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• v.24 no.12
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• pp.93-101
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• 2008

This paper presents the results of numerical investigation on support mechanism of geogrid-encased stone columns for use in soft ground improvement. A number of cases were analyzed using a 3D stress-pore pressure coupled model that can effectively model construction sequence and drainage as well as reinforcing effects of geogrid-encased stone columns. The results indicated that the geogrid encasement provides additional confinement effect that reduces vertical stress in the soft ground, thus resulting in less excess pore water pressures and associated settlement. Also revealed was that such a confinement effect depends on encasement length and stiffness of geogrid. It is also shown that there exist critical encasement length and stiffness of geogrid for a given condition.

• Journal of the Korea Concrete Institute
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• v.25 no.6
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• pp.675-682
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• 2013

In this study, to enhance the quality of concrete surface by removing the surplus water, permeable liner attached the euroform was applied for manufacturing concrete specimens. Various kinds of concrete mixtures with different water to binder ratios were applied and the strength properties of the hardened concrete surfaces were evaluated at different heights. Experimental results showed that the rebound values by schmidt hammer test and the compressive strengths on the surfaces of concrete specimens were increased as proportion to the amount of mixture water which is dependent on the water to binder ratio of each concrete mixture, and more enhancements were observed on the middle and lower specimen surfaces than the upper region. SEM analysis also showed that much denser hydrate structures were observed on the specimen surfaces by the application of the permeable liner while similar hydrate formations were occurred regardless of surface treatment conditions. From the MIP test results of the concrete surfaces, it was observed that, by the application of permeable liner, the pore volume below $0.01{\mu}m$ was decreased with a maximum of 50% resulting in the densification of pore structures.

• Geomechanics and Engineering
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• v.8 no.4
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• pp.559-594
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• 2015

A nonlinear creep function incorporated into the elastic visco-plastic model may describe the long-term soil deformation more accurately. However, by applying the conventional procedure, there are challenges to determine the model parameters due to limitation of suitable data points. This paper presents a numerical solution to obtain several parameters simultaneously for a nonlinear elastic visco-plastic (EVP) model using the available consolidation data. The finite difference scheme using the Crank-Nicolson procedure is applied to solve a set of coupled partial differential equations of the time dependent strain and pore water pressure dissipation. The model parameters are determined by applying the algorithm of trust-region reflective optimisation in conjunction with the finite difference solution. The proposed method utilises all available consolidation data during dissipation of the excess pore water pressure to determine the required model parameters. Moreover, the reference time in the elastic visco-plastic model can readily be adopted as a unit of time; denoting creep is included in the numerical predictions explicitly from the very first time steps. In this paper, the settlement predictions of thick soft clay layers are presented and discussed to evaluate and compare the accuracy and reliability of the proposed method against the graphical procedure to obtain the model parameters. In addition, comparison of the available experimental results to the numerical predictions confirms the accuracy of the numerical procedure.

• Journal of Korean Tunnelling and Underground Space Association
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• v.16 no.2
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• pp.261-267
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• 2014

Various types of external loads can be applied to the tunnel structure. In a shield tunnel, the vibration from the train may affect the behavior of the adjacent ground. In this study, the railway-induced vibration was estimated and applied to the shield tunnel through 3D numerical simulation. The effective stress analysis based on the finite difference method and Finn model was performed to investigate the potential of liquefaction below the tunnel. Furthermore, pore water pressure and displacement were monitored on a time domain; consequently, the liquefaction potential and dynamic response of the shield tunnel were analyzed. Consequently, it is confirmed that the generation of excess pore water pressure by train-induced vibrating load, however, the amount does not meaningfully affect the potential of liquefaction.

• Journal of the Korean Society of Environmental Restoration Technology
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• v.3 no.1
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• pp.52-61
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• 2000

Permeability is important factor in the geotechnical problems, such as seepage discharge and dissipation of excess pore water pressure. The Kozeny-Carman equation works well for graded soils but serious discrepancies are found in clays. Major factor for these discrepancies is the tortuous flow path and unequal pore size. To estimate the permeability of fine grained soils, a permeability equation in which swelling potential is coupled with Kozeny-Carman equation is proposed in this study. To verify proposed equation, a series of variable head permeability test was carried out for steel making slag and sludge mixed with bentonite. The coefficients of permeability which is measured in the laboratory is compared with the values by the proposed equation. From the comparison, it is shown that the proposed equation can predict the coefficient of permeability of clays with satisfaction. As steel making slag and sludge is industry waste, it is reused as material of road foundation and cement but the rate of use is low. It mixed sodium-bentonite with high swelling property and permeability decrease effect. Then, Admixture investigates reuse possibility as liner of waste fill.

• Journal of the Korean Geotechnical Society
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• v.32 no.9
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• pp.37-50
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• 2016

Gravel compaction pile (GCP) is widely used as it increases the bearing capacity of soft ground and reduces the consolidation settlement. Stress concentration ratio for GCP design is dependent on the area replacement, surcharge pressure and depth. However, a range of stress concentration ratio obtained through field, laboratory experiments and numerical analysis is large. Little study has been done on the stress concentration ratio for the mixing ratio of gravel and sand. The main objective of the study is to evaluate the stress concentration ratio for both area replacement ratio and mixing ratio through literature review and numerical analysis. Numerical analysis using the finite element program ABAQUS 6.12-4 has been performed for the composite ground with GCP. The excess pore water pressure and stress concentration ratio of composite ground have been analyzed for both the area replacement ratio and the mixing ratio. Based on the previous research results, a range of stress concentration ratio obtained from the field tests, laboratory tests, numerical analysis on the GCP studies is found to be 1.7-3.2, 2.0-7.5 and 2.0-6.5, respectively. Based on the numerical analysis results, as the area replacement ratio increases, the stress concentration ratio increases up to 30% and then decreases at 40%. Also, the stress concentration ratio tends to increase up to 70:30 and then to decrease after 60:40.

• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.107-121
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• 2003

When the seismic stability of quay walls is analyzed, the magnitudes of force components acting on quay walls during earthquakes and the phase relations among these force components must be properly evaluated. In general, force components include inertia force of the quay wall, lateral earth force, and water force. The magnitude and the phase relation of each force component vary according to the magnitude of the excess pore pressures developed in backfill soils of the quay wall. The dynamic thrust mobilized at the contact surface between the backfill soil and the wall develops as a result of the interactions among these force components. We propose a simple model to evaluate the magnitude and phase variation of the dynamic thrust on the back of the wall in terms of the excess pore pressure. The proposed model can predict the dynamic thrust by summing the magnitudes of farce components calculated from design equations for seismic pressures on the wall. The proposed model was verified by comparing its results with the results from a series of shaking table tests.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2002.03a
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• pp.67-74
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• 2002

An experimental assessment on the dynamic behavior of saturated sand which can consider the irregular characteristics of earthquakes was proposed. The equivalent uniform stress concept presented by Seed and Idriss has been applied to evaluate the liquefaction resistance strength to simplify earthquake loading. However, it was known that the liquefaction resistance strength of soil based on the equivalent uniform stress concept can't exactly mirror the dynamic characteristics of the irregular earthquake motion. In this study, estimation of the criterion of the liquefaction resistance strength was determined by applying real earthquake loading to the cyclic triaxial test. From the test results, relationships between excess pore water pressure and the earthquake characteristics such as magnitude or duration were determined. Magnitude scaling factors to determine the soil liquefaction resistance strength in seismic design were also proposed.

• Geomechanics and Engineering
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• v.4 no.4
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• pp.243-249
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• 2012

In the companion paper, the nonlinear consolidation of soft clays subjected to cyclic loading was analytically investigated. This paper reports the results of an experimental program conducted to verify some critical assumptions made in the analytical study. It, also, includes a numerical study carried out to examine the capability of the proposed theory to determine the consolidation characteristics of soft clays subjected to cyclic loading. Results show that the permeability of the soft clays does not significantly change during the cyclic loading. It is also shown that, compared to the Terzaghi's solution for a linear clay, the inherit nonlinearity of the clay tends to decrease the degree of consolidation due to the smaller rate of dissipation in the excess pore water pressure.

• Geomechanics and Engineering
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• v.16 no.3
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• pp.233-245
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• 2018

Interest to basal reinforced piled embankments is increasing recently due to their rapid construction and reliability. A comprehensive parametric study is conducted to determine effects of pile properties, reinforcement stiffness, embankment properties and soft soil properties into settlements, pressures and excess pore water pressure development and dissipations. Results which are obtained by using one-layer reinforcement during construction are compared with the results obtained by using two-layer reinforcement during construction. Finite element method is used during the parametric study. Second layer of reinforcement is placed in five different positions in order to reveal effects of reinforcement position into behaviour. Traffic load is also taken into consideration during the study. Differences between the results without presence of traffic loading and with presence of traffic loading is stated in this the study.