• 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.

• Geomechanics and Engineering
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• v.18 no.5
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• pp.503-513
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• 2019

In the present, the liquefaction potential of fiber-reinforced sandy soils was investigated through the energy-based approach by conducting a series of strain-controlled cyclic simple shear tests. In the tests, the effects of the fiber properties, such as the fiber content, fiber length, relative density and effective stress, and the test parameters on sandy soil improvement were investigated. The results indicated that the fiber inclusion yields to higher cumulative liquefaction energy values compared to the unreinforced (plain) ground by increasing the number of cycles and shear strength needed for the liquefaction of the soil. This result reveals that the fiber inclusion increases the resistance of the soil to liquefaction. However, the increase in the fiber content was determined to be more effective on the test results compared to the fiber length. Furthermore, the increase in the relative density of the soil increases the efficiency of the fibers on soil strengthening.

• 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.

• 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.

• Geomechanics and Engineering
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• v.37 no.2
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• pp.123-133
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• 2024

This study investigates the effects of loading frequency (f) and specimen size on the liquefaction resistance of clean sand. A series of cyclic direct simple shear tests were conducted on Jumunjin sand with varying consolidated relative densities (40% and 80%), f values (0.05, 0.10, and 0.20 Hz), and diameter to height (D/H) ratios (3.63, 3.18, 2.82, and 2.54). The results demonstrated the significant influence of f and D/H ratio on the number of cycles to liquefaction (N_cyc-liq) and the cyclic resistance ratio (CRR₁₅). It was observed that increasing f linearly increased N_cyc-liq. Increasing the specimen height also led to higher N_cyc-liq values irrespective of the f or relative density. Moreover, a positive correlation between CRR₁₅ and f indicated that higher f yielded higher CRR₁₅. This relationship was more pronounced in dense sand than in loose sand. Specimen height also significantly affected CRR₁₅, with increasing the specimen height resulting in higher CRR₁₅ values. Furthermore, the effect of f on CRR₁₅ was less significant compared to the influence of specimen height. The effect of f on the normalized cyclic resistance ratio (NCRR) was relatively negligible for loose sand but more substantial for dense sand depending on the D/H ratio. Data analysis revealed that the NCRR generally decreases as the D/H ratio increases. An interpolation formula was provided to calculate the NCRR based on the D/H ratio regardless of the f and relative density.

• Journal of the Korean Geotechnical Society
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• v.22 no.12
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• pp.89-98
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• 2006

In this paper the behavior of saturated sand deposits where liquefaction occurred before is studied for successive earthquakes. The relationship between past pore pressure generation and reliquefaction resistance is examined by using cyclic direct simple shear tests. If the soil sample in direct simple shear produced nearly 90% of excess pore pressure during first time loading, its liquefaction resistance increased during following cyclic loading after consolidation. However, a fully liquefied soil during first time loading has a densely packed condition but shows less liquefaction resistance for the following cyclic loading. UBCSAND model that can account for pore pressure change and stiffness loss of soil during shaking is used to analyze the centrifuge test simulating reliquefaction. The pore pressure rise during first time cyclic loading controls liquefaction resistance. The measurements from reliquefaction centrifuge test are compared with numerical predictions. By considering frequent earthquakes having occurred at the Southern Korea near Japan, such effective stress approach is necessary for reliquefaction study.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.590-599
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• 2006

In this study, Liquefaction characteristics of saturated sand under various dynamic loadings such as sinusoidal loading, increasing wedge loading, and real earthquake loading were investigated focusing on the dissipated energy. From the results of cyclic triaxial test, liquefaction resistance strength was calculated by the concept of energy according to the type of input loading. Liquefaction resistance strength was expressed in accumulated dissipated energy calculated from stress-strain curve(hysteresis loop). The dissipated energy according to loading type was compared and the energy-based evaluation was proposed. The procedures are presented in terms of normalized energy demand(NED), normalized energy capacity(NEC), and factor of safely, where NED is the load imparted to the soil by the loading(both amplitude and duration), NEC is the demand required to induce liquefaction, and factor of safely is defined as the ratio of NEC and NED.

• Geomechanics and Engineering
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• v.20 no.3
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• pp.243-254
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• 2020

Due to the permanent damage to structures during earthquakes, soil liquefaction is an important issue in geotechnical earthquake engineering that needs to be investigated. Typical examples of soil liquefaction have been observed in many earthquakes, particularly in Alaska, Niigata (1964), San Fernando (1971), Loma Prieta (1989), Kobe (1995) and Izmit (1999) earthquakes. In this study, liquefaction behavior of uniform sands of different grain sizes was investigated by using the energy-based method. For this purpose, a total of 36 deformation-controlled tests were conducted on water-saturated samples in undrained conditions by using the cyclic simple shear test method and considering the relative density, effective stress and mean grain size parameters that affect the cumulative liquefaction energy. The results showed that as the mean grain size decreases, the liquefaction potential of the sand increases. In addition, with increasing effective stress and relative density, the resistance of sand against liquefaction decreases. Multiple regression analysis was performed on the test results and separate correlations were proposed for the samples with mean grain size of 0.11-0.26 mm and for the ones with 0.45-0.85 mm. The recommended relationships were compared to the ones existing in the literature and compatible results were obtained.

• Journal of the Korean Geotechnical Society
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• v.15 no.4
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• pp.133-152
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• 1999

The cyclic triaxial test was carried out to research liquefaction characteristics and sample disturbance effects of silty sand soils at the west coast in Korea. First, liquefaction in silty sand was generated when axial strain approached to $\pm10%$ of strain and behavior of pore pressure was similar to the formula suggested by Seed, Martin, and Lysmer(1975). Also, it was found that dilatancy was generated at failure. Secondly, the liquefaction evaluation methods suggested by many researchers were carried out and the results were compared. In these methods the weak depth in liquefaction was similar and the method carried out by cyclic triaxial test on remolded sample showed the least safety factor. Thirdly the stress ratio by cyclic triaxial test was compared with that obtained from SPT N-value as a kind of empirical methods. It was found that the effect of sample disturbance was relatively small when SPT N-value was less than 20, but there were large differences in safety factor and resistance of liquefaction in soil by the effects of disturbance and remolding when SPT N-value was more than 20.

• 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.