• Journal of the Korean Geotechnical Society
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• v.36 no.9
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• pp.21-32
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• 2020

In this study, series of cyclic triaxial tests and shear velocity measurement were conducted using Pohang sand, which was taken from liquefaction observed area, to verify the liquefaction characteristics of Pohang. The cyclic resistance ratio(CRR) was derived based on the test results. A specimen was reconstituted into 40% and 80% relative density conditions and then a series of cyclic triaxial tests and shear-wave velocity measurement were conducted. As a result, the effect of particle distribution and relative density to liquefaction resistance was verified. The liquefaction resistance of Pohang sand was evaluated by comparing with other liquefaction resistance of sands from previous research. In addition, the liquefaction resistance curve from field observation data was used to verify the reliability of results from this study by measured shear-wave velocity.

• The Journal of Engineering Geology
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• v.31 no.4
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• pp.493-506
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• 2021

Liquefaction refers to a phenomenon in which excessive pore water pressure occurs when a dynamic load such as an earthquake rapidly acts on a loose sandy soil saturated with soil, and the ground loses effective stress and becomes liquefied. The indoor repeated test for liquefaction evaluation can be confirmed through the repeated triaxial compression test and the repeated shear test. In this regard, this study tried to confirm the liquefaction resistance strength according to the relative density and particle size distribution of sand using the repeated triaxial compression test. As a result of the experiment, it was confirmed that the liquefaction resistance strength increased as the relative density increased regardless of the soil classification, and the liquefaction resistance strength according to the particle size distribution of the sand was confirmed that the liquefaction resistance strength of the SP sample close to SW was significantly higher. In addition, as a result of analyzing 30% of fine powder compared to 0% of fine powder, as the relative density increased to 40~70%, the liquefaction resistance strength decreased by 5~20%, and the domestic weathered soil ground had a fine liquefaction resistance strength compared to Jumunjin standard sand. When the minute was 10%, it was measured to be 30% or more, and when the fine particle was 30%, it was measured to be less than 50%.

• Journal of the Korean Geosynthetics Society
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• v.13 no.2
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• pp.49-57
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• 2014

In this study, in order to take advantage of samples collected in the Jangbogo station, and to grasp the liquefaction resistance characteristics of the dynamic load was performed cyclic triaxial test. Also, through the comparison with the existing literature. The test results, for the relationship between number of cycles for the same cyclic shear stress ratio and the cyclic shear stress ratio to produce an axial strain of 5%, in all samples, the cyclic shear stress ratio to liquefaction for the specimen, which has been liquefied, was increased, whereas number of cycles were reduced. The cyclic shear stress ratio of samples first decrease up to the fine content of about 10%. After this strength level, there is a little increase in cyclic shear stress ratio with increasing fine content. In addition, the cyclic shear stress ratio between cohesive strength, mean particle size, and friction angle decrease but some time later, there was a tendency that cyclic shear stress ratio is a little increased.

• Journal of the Korean Geotechnical Society
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• v.38 no.9
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• pp.35-44
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• 2022

The cyclic triaxial strength test is commonly applied as a laboratory test for evaluating the liquefaction resistance ratio. However, the test procedure was not standardized in South Korea until recently; thus, the test results could significantly differ depending on the performer and apparatus, even when identical soil is used. In this study, the American and Japanese standards for the cyclic triaxial strength test were analyzed and the Korean standard was developed considering domestic circumstances. To verify the effectiveness of the standardization of liquefaction laboratory tests, several cases of cyclic triaxial strength tests were conducted and analyzed (1) following the Korean standard and (2) without following any specific instructions for the test procedure. Under (1), the deviation of the liquefaction resistance ratio dramatically decreased.

• Journal of the Korean Geotechnical Society
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• v.21 no.7
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• pp.13-20
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• 2005

For experimental study on the effect of particle size distribution on the liquefaction resistance strength, particle size distribution curves of the dredged soil were investigated. In this process, four mean particle sizes and three uniformity coefficients were defined representatively and twelve representative particle size distribution curves which have different mean particle size and uniformity coefficient, were defined and manufactured by using the real dredged river soil. Cyclic triaxial tests and resonant column tests were carried out to analyze the effect of mean particle size and uniformity coefficient on the liquefaction resistance strength and dynamic characteristics.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.3C
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• pp.93-102
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• 2011

Most experimental studies on soil liquefaction are related to clean sands. However, soils in the field or reclaimed grounds commonly contain some amounts of silt and clay rather than clean sand only. Many researchers investigated the effect of fine contents on liquefaction resistance and mainly used non-plastic fines such as silts. In this study, 10% of plastic fines with various plasticity index (PI) such as 8, 18, 50, and 377 were mixed with wet Nakdong River sand and then loose, medium, and dense specimens were prepared by undercompaction method. A series of undrained cyclic triaxial tests were carried out by applying three different cyclic stress ratios. As a result, the liquefaction resistance tended to decrease as a PI of fines in the specimens with equal fine content increased. On the other hand, the difference between loose specimens with low and high plasticity fines was not clearly observed in terms of liquefaction resistance. However, in the case of dense specimens, liquefaction resistance decreased up to 40% as a plasticity of fines increased.

• Journal of the Korean Geotechnical Society
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• v.26 no.2
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• pp.5-14
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• 2010

In this study, cyclic triaxial tests were performed under anisotropically consolidated condition by using irregular earthquake loading to consider in-situ condition and seismic wave. Jumunjin sand with a relative density 50 percent was used in the tests. The consolidation pressure ratio (K) was changed from 0.5 to 1.0. The Ofunato and Hachinohe wave were applied as irregular earthquake loadings and liquefaction resistance strengths of each specimen were estimated from the excess pore water pressure (EPWP) ratio. As a results of the cyclic triaxial tests, EPWP ratio increased with increased K value. It shows that isotropically consolidated sand is more susceptible to liquefaction than anisotropically consolidated sand under equal confining pressure and dynamic loadings. From the test results, the relationship between K and EPWP ratio normalized by effective confining pressure and deviator stress was proposed. And a new factor which corrects the liquefaction resistance strength for the in-situ stress condition is proposed.

• Journal of the Korean Geotechnical Society
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• v.37 no.12
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• pp.107-116
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• 2021

In this study, a set of laboratory liquefaction test has been conducted using undisturbed samples collected from Songlim-park, Pohang where liquefaction phenomenon had been observed in 2017. Soil samples were frozen right after tube sampling to minimize the disturbances during transport, storage, and test preparation. Cyclic triaxial test has been carried out to evaluate the liquefaction resistance ratio of undisturbed soil samples. As a result, the liquefaction resistance ratio of samples collected from 8.0~8.8 m and 11.0~11.8 m were almost similar, and these values were approximately 0.04~0.07 larger than values estimated by simplified assessment method using field test results. It is expected that the application of undisturbed sample for the evaluation of liquefaction resistance could contribute to the economical design of geotechnical structures.

• Journal of the Korean Geotechnical Society
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• v.17 no.6
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• pp.235-244
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• 2001

Liquefaction may be caused by sudden decrease in the soil strength under undrained conditions. This loss of soil strength is related to the development of excess pore pressures. During this study, fines content affects the maximum and minimum void ratios are investigated. The results of static and cyclic triaxial test on silty saturated sands are presented. These tests are performed to evaluate liquefaction strength and static and cyclic behavior characteristics. The samples are obtained from Saemangeum and drying on air. The main results are summarized as follows : 1) The maximum and minimum void ratio lines follow similar trends. 2) Maximum and minimum void ratios are established at 20~30% fines content. 3) As confining pressures and overconsolidation ratio are increased, the resistance to liquefaction are increased. 4) Instability friction angles are increased with increasing initial relative density. 5) The resistance to liquefaction are decreased with increasing effective stress ratio.

• Journal of the Earthquake Engineering Society of Korea
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• v.10 no.3 s.49
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• pp.125-134
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• 2006

Conventional methods for the assessment of liquefaction potential were primary for severe earthquake regions $(M{\geq}7.5)$ such as North America and Japan. In Korea, an earthquake related research has started in 1997, but most contents in the guidelines were still quoted from literature reviews of North America and Japan, which are located in strong earthquake region. Those are not proper in a moderate earthquake regions including Korea. Also the equivalent uniform stress concept (Seed & Idriss, 1971) using regular sinusoidal loading which is used, in a conventional method for the assessment of liquefaction potential, can't reflect correctly the dynamic characteristics of real irregular earthquake motions. In this study, cyclic triaxial tests using irregular earthquake motions are performed with different earthquake magnitudes, relative densities, and fines contents. Assessment of liquefaction potential in moderate earthquake regions is discussed based on various laboratory test results. From the results, screening limits in seismic design were re-investigated and proposed using normalized maximum stress ratios under real irregular earthquake motions. Also from the tests using constant wedge loading and incremental wedge loading, the characteristics of liquefaction resistance of saturated sand under irregular ground motions are investigated.