• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.129-136
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• 2001

본 논문에서는 석탄회 매립지반의 액상화 가능성을 평가하기 위해 순수 모래시료와 더불어서 모래시료와 석탄회가 혼합된 모래시료에 대한 일련의 진동삼축실험을 변형률제어 방법으로 수행하였다. 실험결과 진동하중에 의해서 시료 내에 발생하는 간극수압의 크기는 작용하는 전단변형률의 크기에 심각하게 영향을 받고, 작용하는 전단변형률이 지반의 한계전단변형률 보다 작은 경우에는 진동수가 높은 조건에서도 간극수압이 발생하지 않음을 알았다. 또한 전단변형률이 약 0.1%보다 작고 한계전단변형률에 가까운 경우에는 순수 모래시료와 비교하여 본 논문에서 조사한 석탄회 함유율 범위 (10%~30%)의 시료에서 간극수압이 더 크게 발생하였다. 반면에, 전단변형률이 큰 경우에는 순수 모래시료에서 간극수압이 크게 발생하는 추세를 보였다. 반복 전단에 따른 간극수압의 발생량은 전반적으로 석탄회 함유율이 증가할수록 커지는 경향을 보였다. 이러한 결과를 근거로 해안이나 하천에 인접한 한계지 개발에 있어서 사질토에 석탄회를 혼합 매립하여 지반을 조성하는 경우에 액상화에 대해서 불안정한 지반이 될 가능성이 있는 것으로 판단되었다.

• Journal of the Korean GEO-environmental Society
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• v.11 no.11
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• pp.55-62
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• 2010

The settlements by liquefaction seldom occur uniformly because of soil homogeneity, however differential settlements are major cause of the damages to structures. From the past researches, author paid attention to the fact that stress history during undrained cyclic shear process affects greatly on the volumetric strains of the post-liquefaction. Therefore, the effect of the residual shear strain in cyclic shear process was examined in this study. The experiment apparatus based on strain control with volumetric strain control device was used for the study to investigate the effect of the residual strain on the relationship between volumetric strain and effective stress of clean and granite sandy soil. It could be seen an insignificant difference in the volumetric strain after liquefaction under various residual shear strain conditions in the case of clean sand. On the other hand, in granite sandy soil, the volumetric strain after liquefaction was small when the lower level of the residual shear strain was applied. And, the residual shear strain during cyclic shear affected the shape of the relation curve between effective stress and volumetric strain as well.

• Journal of the Korean Geotechnical Society
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• v.18 no.1
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• pp.91-99
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• 2002

In this study, a new methodology for the assessment of liquefaction potential is proposed. Since there is no data on the liquefaction damage in Korea, the dynamic behavior of fully saturated soils is characterized through laboratory dynamic tests. There are two experimental parameters related to the soil liquefaction resistance characteristics : the one is the index of disturbance determined by $G/G_{max}$ curve and the other is a plastic shear strain trajectory evaluated from stress-strain curve. The proposed methodology takes advantage of the site response analysis based on real earthquake records to determine the driving effect of earthquake. In the evaluation of liquefaction resistance characteristics, it is verified experimentally that the magnitude of cyclic shear stress has no influence on the critical value of plastic shear strain trajectory at which the initial liquefaction occurs. Cyclic triaxial tests under the conditions of various cyclic stress ratios and torsional shear tests are carried out far the purpose of verification. Through this study, the critical value at the initial liquefaction is found unique regardless of the cyclic stress ratio. It is also f3und that liquefaction resistance curve drawn with disturbance and plastic shear strain trajectory can simulate the behavior of fully saturated soils under dynamic loads.

• Korean Journal of Mineralogy and Petrology
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• v.33 no.3
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• pp.185-193
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• 2020

There have been many studies on the calcination of oyster shells in the perspective of recycling of resources. The quicklime made by the calcination of oyster shells is used either as it is or after reacting with water to transform to liquid lime before being used. However, the liquid lime made from calcined oyster shells show slightly different properties from that of limestone. In this study, to compare these properties of oyster shell with those of limestone, the samples were calcined and reacted with water at various temperatures to transform to a liquid lime and filtered using 150 ㎛ sieves to calculate the transform rate to liquid lime. The calcined limestone was transformed to liquid lime at all temperatures, but calcined oyster shell did not show any transformation at 30℃ and 50℃ under the experimental conditions of this study, and rather increased the weight for the remaining after filtration due to the presence of Ca(OH)₂ produced by the reaction with water, Even at 90℃, the transformation rate of calcined oyster shell to liquid lime was lower than that of limestone. This difference in oyster shell can be explained partly by the preventing calcined one from reacting with water by conchiolin which is protein found in the prismatic and pearl layers of oyster shell. Conchiolin is also known to be stable and does not decompose even at high temperature. However, even the calcined chalk layer without conchiolin shows lower transformation rate than that of calcined limestone, probably due to the small amount of Na in oyster shell, which may cause additional reaction including eutectic melt during calcination process.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.147-158
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• 2004

Laboratory dynamic tests are carried out to assess the liquefaction potential of saturated sands in most countries. However, simple results such as the maximum cyclic shear stress and the number of cycles at initial liquefaction are used in the experimental assessment of liquefaction potential, even though various results can be obtained from the dynamic test. In addition, it seemed to be inefficient because more than three dynamic tests with different stress ratio have to be carried out to draw a liquefaction resistance experimental curve. To improve the present assessment method fur liquefaction potential, a new critical resistible characteristic far soil liquefaction is proposed and verified through conventional cyclic triaxial tests with Jumunjin sand. In the proposed method, various experimental data such as effective stress path, stress-strain relationship, and the change of excess pore water pressure can be used in the determination of cumulative plastic shear strains at every 1/4 cycle. Especially, the critical cumulative plastic shear strain to initiate liquefaction can be defined in a specific point called a phase change point in the effective stress path and it can be calculated from a hysteric curve of stress-strain relationship up to this point. Through this research, it is found that the proposed cumulative plastic shear strain can express the dissipated energy to resist dynamic loads and consider the realistic soil dynamic behavior of saturated sands reasonably. It is also found that the critical plastic shear strain can be used as a registible index of soils to represent the critical soil dynamic state, because it seems to include no effect of large deformation.

• Journal of the Korean Geotechnical Society
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• v.20 no.5
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• pp.145-159
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• 2004

The conventional method for assessment of liquefaction potential proposed by Seed and Idriss has been widely used in most countries because of simplicity of tests. Even though various data such as stress, strain, stress path, and excess pore water pressure can be obtained from the dynamic test, especially, two simple experimental data such as the maximum deviatoric stress and the number of cycles at liquefaction have been used in the conventional assessment. In this study, a new detailed assessment for liquefaction potential to reflect both characteristics of real earthquake motion and dynamic soil resistance is proposed and verified. In the assessment, the safety factor of the liquefaction potential at a given depth of a site can be obtained by the ratio of a resistible cumulative plastic shear strain determined through the performance of the conventional cyclic test and a driving cumulative plastic shear strain calculated from the shear strain time history through the ground response analysis. The last point to cumulate the driving plastic shear strain to initiate soil liquefaction is important for this assessment. From the result of cyclic triaxial test using real earthquake motions, it was concluded that liquefaction under the impact-type earthquake loads would initiate as soon as a peak loading signal was reached. The driving cumulative plastic shear strain, therefore, can be determined by adding all plastic shear strains obtained from the ground response analysis up to the peak point. Through the verification of the proposed assessment, it can be concluded that the proposed assessment for liquefaction potential can be a progressive method to reflect both characteristics of the unique soil resistance and earthquake parameters such as peak earthquake signal, significant duration time, earthquake loading type, and magnitude.

• Journal of the Korean Geotechnical Society
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• v.36 no.6
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• pp.35-46
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• 2020

The input parameters for numerical simulation of the liquefaction phenomenon need to be properly evaluated from laboratory and field tests, which are difficult to be performed in practical situations. In this study, the numerical simulation of the cyclic direct simple shear test was performed to analyze the applicability of Finn and PM4Sand models among the constitutive models for liquefaction simulation. The analysis results showed that the Finn model properly predicted the time when the excess pore water pressure reached the maximum, but failed to simulate the pore pressure response and the stress-strain behavior of post-liquefaction. On the other hand, the PM4Sand model properly simulated those behaviors of the post liquefaction. Finally, the evaluation procedure and the equations of the input parameters in the PM4Sand model were developed to mach the liquefaction cyclic resistance ratio corresponding to design conditions.

• Journal of the Korean Geotechnical Society
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• v.23 no.10
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• pp.47-56
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• 2007

In this research, the effects of the gravel content on the liquefaction behavior for both of the isotropically and $K_0-anisotropically$ consolidated gravel-sand mixtures are investigated. for this purpose, the cyclic triaxial tests for the specimens with the same relative density (Dr=40%) and variations of gravel content were performed. On the other hand, a series of undrained cyclic triaxial tests were carried out on the isotropically consolidated gravel-sand mixtures with the same void ratio (e=0.7) and from 0% to 30% gravel contents. Void ratios of gravel-sand mixtures with the same relative density (Dr=40%) are found to decrease significantly with the increase of the gravel content from 0% to about 70% and increase thereafter. But the void ratio of the sand matrix among the gravel skeleton increases with the increase of the gravel contents. Test results are as follows : for the isotropically consolidated specimen with 40% of relative density and low gavel contents (GC=0%, 20%, 40%), pore water pressure development and axial strain behavior during undrained cyclic loading show similar behavior to those of the loose sand because of high void ratio, and the specimens with high gravel content (70%) both pore pressure and strata behaviors are similar to those of dense sand. And the isotropically consolidated specimens with the same void ratio (e=0.7) and higher gravel contents show the same behavior of pore water pressure and axial strain as that of the loose sand, but for the lower gravel content this behavior shows similar behavior to that of dense sand. The liquefaction strength of the isotropically consolidated specimens with the same relative density increases with gravel content up to 70%, and the strength decreases with the increase of the gravel content at the same void ratio. Thus, it is confirmed that the liquefaction strength of the gravel-sand mixtures depends both on relative density and void ratio of the whole mixture rather than the relative density of the sand matrix filled among gravels. On the other hand, the behavior of pore water pressure and axial strain for the $K_0-anisotropically$ consolidated gravel-sand mixtures shows almost the same cyclic behavior of the sand with no stress reversal even with some stress reversal of the cyclic loading. Namely, even the stress reversal of about 10% of cyclic stress amplitude, the permanent strain with small cyclic strain increases rapidly with the number of cycles, and the initial liquefaction does not occur always with less than maximum pore water pressure ratio of 1.0. The liquefaction resistance increases with the gravel contents between 0% and 40%, but tends to decrease beyond 40% of gravel content. In conclusion, the cyclic behavior of gravel-sand mixtures depends on factors such as gravel content, void ratio, relative density and consolidation condition.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.57-60
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• 2006

The instability analysis of submerged gas flow into liquid is studied, which assumes gas and liquid as viscous and irrotational. At low mass flow rate of gas, injected gas plume is collection of bubbles, and increase of gas flow rate makes plume as a jet. It is well known that the transition from bubbling to jetting occurs in the transonic region. But previous works neglect viscous effect of gas flow into liquid. This paper concerns about an application of viscous potential flow theory in cylindrical gas flow into liquid. The growth rate versus wave number and mach number is compared with various condition including inviscid and viscous flow.

• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.65-75
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• 2024

This study investigates liquefaction-induced settlement through strain-controlled tests using a cyclic direct simple shear device on clean sand specimens. By focusing on the accumulated shear strain, soil density, sample preparation method, and cyclic waveshape, this study attempts to enhance the understanding of soil behavior under seismic loading and its further deformation. Results from tests conducted on remolded samples reveal insights into excess pore water pressure development and post-liquefaction volumetric strain behavior, with denser samples exhibiting lower volumetric strains than looser samples. Similarly, the correlation between the frequency and amplitude variations of the wave and volumetric strain highlights the importance of wave characteristics in soil response, with shear strain amplitude changes, varying the volumetric strain response after reconsolidation. In addition, samples prepared under moist conditions exhibit less volumetric strain than dry-reconstituted samples. Overall, the findings of this study are expected to contribute to predictive models to evaluate liquefaction-induced settlement.