• Journal of the Korean Geotechnical Society
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• 제36권6호
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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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• 제32권6호
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• pp.49-59
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• 2016

We develop liquefaction resistance curves, which represent the correlation between cyclic resistance ratio (CRR) and number of cycles (N) to estimate the build-up of residual excess pore pressure from simple shear tests performed for this study and also from published literature. The liquefaction curve is calculated from two models. The comparisons show that one of the models is not reliable because it underestimates CRR. The scatter of the data is shown to be significantly reduced when CRR is normalized to the resistance ratio at N = 15 ($CRR_{N=15}$). Use of the normalization is particularly useful because CRR can be easily estimated from field tests. From normalization, we propose mean, upper, and lower curves. The corresponding design equation and its parameters are also proposed. We believe that the proposed curves can be used for effective stress site response analyses and evaluation of the seismic performance of port structures.

• KSCE Journal of Civil and Environmental Engineering Research
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• 제28권2C호
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• pp.83-94
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• 2008

In this study an effective stress analysis was performed to evaluate liquefaction potential and ground settlement for reclaimed sites. The effective stress model can simulate the stiffness degradation due to excess pore pressure and resulting ground deformation. It is applicable to a wide range of strain. An equivalent linear analysis suitable for low strain levels was also carried out to compare the effective stress analysis. Shear stress ratio calculated from an equivalent linear analysis was used to determine SPT blow count to prevent liquefaction. Depending on the magnitude of potential earthquake and fine contents, the SPT blow count was converted into an equivalent cone tip resistance. It was compared with the measured cone tip resistance. The measured elastic shear wave velocity and cone tip resistance from two reclaimed sites in Incheon were used to perform liquefaction analyses. Two liquefaction evaluation methods showed similar liquefaction potential which was evaluated continuously. The predicted excess pore pressure ratio of upper 20 m was between 40% and 70%. The calculated post-shaking settlement caused by excess pore pressure dissipation was less than 10 cm.

• Journal of the Korean Geosynthetics Society
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• 제13권2호
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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.

• Proceedings of the Korean Geotechical Society Conference
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• 한국지반공학회 2005년도 춘계 학술발표회 논문집
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• pp.1528-1537
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• 2005

The purpose of this study is investigated the method for estimation of the liquefaction on the reclaimed land, located in Incheon and assessed the ability of liquefaction under the condition of criteria, which is the magnitude '6.5' of seismic on the basis of the domestic seismic characteristics. Performed not only field test but the experiment as well to study how the fine content would affect into the dreging and reclaimed land and also estimated the safety factor through the empirical method and anticipated detail method based on the results. Within the reclaimed land, there are many sized soils which are almost extended from well-graded silty sand(SM) to poor-graded fine grained sand, and which have the condition, so called, the liquefaction which is easily to bring into under the circumstances within the ground. However, partly, now that the soil is mixed with silt and silty clay which include the content of fine grained dust quite a bit, the difficulties and inconveniences has been expected while trying to find the ratio of cyclic resistance, but finally Seed and Idriss method showed the most way when we estimate the safety factor on the liquefaction.

• Journal of the Korean Geotechnical Society
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• 제15권4호
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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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• 제18권1호
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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.

• Proceedings of the Korean Geotechical Society Conference
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• 한국지반공학회 2003년도 봄 학술발표회 논문집
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• pp.315-322
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• 2003

Cyclic simple shear tests were performed to find out the effect of preshear on dynamic strength of the sandy soil. Tests were performed for the specimens with 40% and 60% of relative density, under three different effective vertical stress of 50, 100 and 200kPa. For 50 and 100kPa, preshear ratios 0.00, 0.08, 0.12 and 0.16 were given, respectively, For low and high relative densities, two different results are shown in dynamic tests. Under the dense conditions, the maximum shear stress ratio($\tau$$\_$cyc//$\sigma$$\_$vo/) and the cyclic shear stress ratio($\tau$$\_$cyc//$\sigma$$\_$vo/) causing a certain shear strain increase with augmenting preshear ratio(${\alpha}$). However, the maximum shear stress ratio and the cyclic shear stress ratio increase or decrease with increasing preshear ratio under the loose conditions. Correction factor(K$\_$${\alpha}$/) for preshear increases at an early stage and then decreases with increasing preshear ratio at loose condition and increase with increasing preshear ratio at dense condition. Correction factor (K$\_$${\alpha}$,Max/) for preshear increases with the increasing preshear ratio irrespective of relative density, and the value of has same behavior as K$\_$${\alpha}$/.

• Journal of the Korean Geotechnical Society
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• 제16권5호
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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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• 제37권8호
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• pp.5-13
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• 2021

Liquefaction behaviors of two natural silty samples containing fines including clay of 50% or more (Sample No.1 was silt 44.1% and clay 8.8%, sample No.2 was silt 57.2% and clay 12.4%) were examined by a cyclic triaxial test. According to the results on samples containing 50% or more of fine particles, an increase in the fine content decreases the liquefaction resistance of the sample. In other words, when the fine content increases, the liquefaction state of sample is reached with a small number of cyclic loads. In the relationship between the excess pore water pressure ratio and the number of cycles, the slope of the excess pore water pressure ratio increases more steeply as the fine content increases. As a result of analyzing the liquefaction behavior of the two silts with the content of clay contained in the fines, liquefaction occurred more easily in the No.2 silt with high clay content. This result shows that the clay contained in the fines affects the liquefaction behavior of the silt.