• Geomechanics and Engineering
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• v.3 no.2
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• pp.83-108
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• 2011

The effect of non-plastic fines (silt) on liquefaction and pore pressure generation characteristics of saturated sands was studied through undrained stress controlled cyclic triaxial tests using cylindrical specimens of size 50 mm diameter and height 100 mm at different cyclic stress ratios and at a frequency of 0.1 Hz. The tests were carried out in the laboratory adopting various measures of sample density through various approaches namely gross void ratio approach, relative density approach, sand skeleton void ratio approach, and interfine void ratio approach. The limiting silt content and the relative density of a specimen were found to influence the undrained cyclic response of sand-silt mixtures to a great extent. Undrained cyclic response was observed to be independent of silt content at very high relative densities. However, the presence of fines significantly influenced this response of loose to medium dense specimens. Combined analyses of cyclic resistance have been done using the entire data collected from all the approaches.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.1206-1213
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• 2009

Earthquake had occurred in the Korean Peninsula about 2,100 times is not well known in the world. With the true liquefaction judgment is well used to in Korea. Through liquefaction judgements were compared with specifications between Korea and Japan, it would be offered some suggestions for liquefaction judgement used in Korea. The proposals were as 1) It can be known that what kind of earthquake will make unstable state between long-term and short-term earthquake if the natural period of ground turned out. In that case, Hachinohe and Ofunato Earthquake wave will need no more. 2) Liquefaction-induced lateral flow or damage for structure should be estimate but it had not performed in Korea. 3) Heavy rain and ocean wave-induced liquefaction also should be examined thoroughly in slope or ocean, respectively.

• Journal of the Korean GEO-environmental Society
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• v.13 no.1
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• pp.21-29
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• 2012

Ground failure by liquefaction can occur not only during shaking but also as the result of the post-liquefaction process after an earthquake. During the process of ground deformation and failure, excess pore water pressure in soil is redistributed, which can then lead to changes in the effective stress of soils. Therefore, in order to provide a further understanding of the phenomenon, we have to estimate the properties of effective stress during the recompression process in post-liquefaction as well, not only the total amount of pore water drained. The primary objectives of this study are to determine and compare the recompression properties in the post-liquefaction process in terms of the relationship between volumetric strains and mean effective stresses under the various conditions of relative density and shear stress history. In all experimental cases, the volumetric strains increase greatly in the low effective stress level, almost to the zero zone, and granite soil, which has fine grains, undergoes gradual changes in the relationship between volumetric strains and mean effective stresses compared with fine sand. And, we can also find that recompression properties in the post-liquefaction process by cyclic loading depend highly on the dissipation energy and maximum shear strain, and this fact can be obtained in all cases regardless of the existence of fine content, relative density, and loading history. Especially, granite soil having fine grains can be defined uniformly in the relationship between dissipation energy and maximum volumetric strain, while fine sand cannot be so uniformly defined.

• Journal of the Korean Geotechnical Society
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• v.16 no.5
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• pp.37-43
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• 2000

보통으로 다져진 실트질 모래(Dr=50%)에 대한 액상화 전후 상태에서의 반복하중에 의한 동적거동을 연구하기 위하여 몇가지의 압밀응력비로서 압밀시킨공시체에 대해서 일련의 일련의 반복삼축시험을 수행하였다. 연구결과로서 압밀응력비가 액상화거동에 미치는 영향을 나타내었으며 또한 액상화 전후의 동적거동을 비교하였다. 그리고 액상화 후의 거동은 선행액상화시의 응력반전여부에 의해서 절대적으로 좌우된다는 사실을 보여주고 있다. 결론적으로 액상화를 경험한 공시체의 액상화저항은 액상화를 경험하지 않은 공시체에 비해서 이방압밀의 경우에는 높고 등방압밀의 경우에는 낮다.

• Journal of the Korean Geotechnical Society
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• v.18 no.4
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• pp.329-337
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• 2002

Based on the equivalent uniform stress concept presented by Seed and Idriss, sinusoidal cyclic loads which simplified the earthquake loads have been applied in evaluating the liquefaction resistance strength experimentally. However, the liquefaction resistance strength of soil based on the equivalent uniform stress concept can not exactly reflect the dynamic characteristics of the irregular earthquake motion. In this study, 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 liquefaction behaviors of saturated sand and earthquake characteristics such as magnitude or time-duration were determined. Magnitude scaling factors to determine the soil liquefaction resistance strength in seismic design were also proposed.

• Geotechnical Engineering
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• v.14 no.1
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• pp.59-70
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• 1998

Samples of silty sands and hydraulic fill ground were investigated by dynamic triaxial teats in order to evaluate the liquefaction strengths. In the tests, (1) undisturbed and disturbed samples were prepared, (2) dynamic shear strengths were measured under isotropic and anisotropic condition, and (3) the test results were compared with the other results which were tested by domestic and foreign researchers. The liquefaction shear strengths under ismtropic test condition were presented in terms of the relative densities. The amount of silt under 30o hardly influenced on the liquefaction strength. In the test results of anisotropically consolidated samples the liquefaction strength was dependent on the magnitude of the effective consolidation ratio. These teat results show that the liquefaction strength of the silty sand in Korea went coast exists within the boundary of the values suggested by Seed and Peacock(1971).

• Journal of the Korean Geotechnical Society
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• v.23 no.10
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• pp.13-22
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• 2007

Recently, many researches on the dissipation of excess pore pressure in liquefied sand grounds have been performed to evaluate post-liquefaction behavior of structures. In this research, centrifuge tests were performed to analyze liquefaction behavior of level saturated sand grounds. Based on the test results, the evaluation model of solidified layer thickness was developed to simulate non-linear variation of the thickness with time. The thickness evaluation model was combined with the solidification theory and the consolidation theory in order to simulate dissipation of excess pore pressure. The suggested dissipation model properly estimated the solidified layer thickness and the time history of excess pore pressure.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.10a
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• pp.361-368
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• 1998

The purpose of this study is to find out the factors affacting liquefaction potential by using DSC(disturded state concept) method and to verify these results through cyclic shear test (truly triaxial test and cyclic triaxial) on saturated sandy soil. Based on this reserch, the DSC method predictions were found to provide satisfactory correlation with the cyclic shear test. And the relationship between the factors affecting liquefaction characteristics--relative density(Dr0 and initial effective confining pressure and physical properties of the saturated sand --ξD and Dc--is found. If the relative density and the initial effective confining pressure increase, the number of cyclic grows up. This means that Dc is incresed and ξD is decreased. Therefore, the liquefaction potential can be evaluated and the factors affacting liquefaction potential can be investigated by using on DSC method. Finally, it is shown that the DSC method can capture the liquefaction mechanism.

• Journal of the Korean Geotechnical Society
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• v.34 no.9
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• pp.5-17
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• 2018

A magnitude 5.4 earthquake struck the city of Pohang, North Gyeongsang Province, South Korea on November 15, 2017. Many sand volcanoes were observed on paddy fields, parks and roads. This phenomenon was the first to be observed as a sign of soil liquefaction in South Korea. In this study, two different kinds of ejected Pohang sands were collected from a liquefied paddy field. Those sands were reconstituted into loose and dense conditions and then a series of cyclic simple shear tests were conducted under confining stresses of 100 and 200 kPa. A real earthquake motion was also repetitively applied to the specimen. As a result of constant shear stress tests, the cyclic resistance ratio (CRR) of loose sand was 0.12-0.14, while the CRR value of dense sand was 0.17-0.21. It was shown that the relative density was more influencing factor on liquefaction resistance than the sand types and initial confining stress. When a real Pohang earthquake motion was repetitively applied to the specimen, a loose sand was liquefied at the second earthquake motion but the dense sand at the third earthquake motion.

• Proceedings of the Korean Society of Disaster Information Conference
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• 2016.11a
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• pp.193-194
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• 2016

지진 발생시에 비교적 큰 규모의 피해를 일으킬 수 있는 것이 지반의 액상화(liquefaction) 발생이다. 지반의 액상화 현상에 대한 연구는 1960년대 이후 세계적으로 괄목할 만한 성과를 얻어왔으며, 최근, 우리나라에서도 본격적으로 현장에서 적용하고 있다. 본 연구를 통하여 현장에서 액상화 평가 및 대책공법 적용까지의 과정을 분석할 수 있었다. 본 연구결과는 향후 유사한 현장에서 적용 가능할 것으로 판단된다.