• Proceedings of the Korean Geotechical Society Conference
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• 1993.06a
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• pp.1-14
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• 1993

Ground reinforcements is the essential method to prevent the liquefaction of loose sand deposit, However, in the construction of the life lines, it is impossible to treat the whole loose deposit against liquefaction. As an countmeasure for the life lines against the liquefaction, a monitorning system can be considered for an immediate judgement of the liquefaction occurrence during an earthquake. Through shaking table tests on model grounds, pore presure developments were investigated in terms of the surface spectral velocity, which was verified as a tool for the immediate judgement of the liquefaction occurrence.

• Journal of the Korean Geotechnical Society
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• v.23 no.8
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• pp.47-57
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• 2007

In this study, the analysis of density characteristics of some dredged and reclaimed ground sites, which is necessary for liquefaction evaluation of a dredged and reclaimed ground, was conducted. From analyzing a simplified liquefaction potential evaluation using SPT-N values which have been applied as domestic earthquake-resistant design criterion, improvement scheme is suggested. Based on the analysis result of density characteristics, it was found out that the relative density and the intial N-value ranged respectively $40{\sim}50%\;and\;5{\sim}8$. In the case of applying Liao & Whitman's equation to correct effective overburden pressure, liquefaction resistance of the upper ground that is relatively weaker than that of lower ground is overestimated. So, Skempton's equation is recommended. And the N value with depth which is applied for design process should be estimated by the exponential equation, $N=1.35{\sigma}'^{0.75}$.

• Geomechanics and Engineering
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• v.17 no.2
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• pp.145-156
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• 2019

Since behaviors of loose, dense, silty sands vary under seismic loading, understanding the liquefaction mechanism of sandy soils continues to be an important challenges of geotechnical earthquake engineering. In this study, 36 deformation controlled cyclic simple shear tests were performed and the liquefaction potential of the sands was investigated using three different relative densities (40, 55, 70%), four different effective stresses (25, 50, 100, 150 kPa) and three different shear strain amplitudes (2, 3.5, 5%) by using energy based approach. Experiments revealed the relationship between per unit volume dissipated energy with effective stress, relative density and shear strain. The dissipate energy per unit volume was much less affected by shear strain than effective stress and relative density. In other words, the dissipated energy is strongly dependent on relative density and effective stress. These results show that the dissipated energy per unit volume is very useful and may contain the non-uniform loading conditions of the earthquake spectrum. When multiple regression analysis is performed on experiment results, a relationship is proposed that gives liquefaction energy of sandy soils depending on relative density and effective stress parameters.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.575-586
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• 2008

The main objective of this paper is to develop an improved model for the analysis of liquefaction potential and to predict excess pore pressure (EPP) using the proposed model that can simulate behavior of saturated sand under earthquake loading conditions. The damage concept is adopted for the development of the proposed model. For the development of the model, a general formulation based on experimental results and damage potential using cumulative absolute velocity (CAV) is proposed for a more realistic description of dynamic responses of saturated sand. Undrained dynamic triaxial tests are conducted using earthquake loading conditions. Based on test results, the NCER-NCW function in terms of $w_d$ and CAV is developed. Procedure for the evaluation of EPP and determination of model parameters for the proposed model is presented as well. For the determination of initial liquefaction, the minimum curvature method using the NCS-NCW curve is proposed. It is observed that predicted initial liquefaction using the proposed method agrees well with measured initial liquefaction. From results of additional undrained dynamic triaxial tests, it is seen that predicted EPP generation using the proposed model agrees well with measured results for earthquake loading cases.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2000.04a
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• pp.105-111
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• 2000

If a saturate sand is subjected to ground vibrations it tends to compact and decrease in volume. if drainage is unable to occur the tendency to decrease in volume results in an increase in pore water pressure and if the pore water pressure build up to the point at which it is equal to the overburden pressure the effective stress becomes zero the sand loses its strength completely. This phenomenon is called "Liquefaction" It is associated primarily but not exclusively with saturated cohesion soils. The attention and study on liquefaction have been growing since the earthquake in Niigita Japan in 1964. Many researchers on liquefaction effect have been carried out in many countries under the potential influence of earthquake including Japan. However little research on liquefaction has been reported in Korea because Korea has been considered to be safe from earthquake. The term "liquefaction" is only known among geotechnical engineers,. In this paper overview of liquefaction and the evaluation on the applicability of vibrated crushed-stone pile as a liquefaction prevention method are presented.ethod are presented.

• Journal of the Korean Geotechnical Society
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• v.34 no.8
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• pp.37-49
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• 2018

Since the observation of ground motions in South Korea, liquefaction manifestation was the first to be observed in Pohang earthquake in 2017 with $M_L$ 5.4. Because liquefaction causes ground settlement and lateral spread damaging in-ground or super structures, various researchers have been analyzing the Pohang liquefaction case history to better understand and predict liquefaction consequence and to prevent future disasters. In prior research at the 2018 EESK conference, a map of Liquefaction Potential Index (LPI), indicating the severity of liquefaction, in Pohang was created and compared with damage observations. The LPI correlated well with the observations, but the severity categorized by LPI range was significantly higher than the actual observations in most regions. The prior LPI map was created evaluating ground motions using the simplified approach. In this research, we perform the effective site response analyses with porewater pressure generation model for the detailed evaluation of liquefaction on the liquefied sites in Pohang. We found that the simplified approach for LPI evaluation can overestimate the severity.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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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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• v.15 no.6
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• pp.307-317
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• 1999

The purpose of this study is to utilize conventional procedures for evaluation of liquefaction potential and to compare the results obtained by modified detailed method based on Korean earthquake magnitude (M=6.5). Liquefaction potential is assessed by comparing liquefaction strength of soil and cyclic shear stress generated in the soil layers during earthquakes. The cyclic shear stress is computed from the earthquake response analysis, and liquefaction strength of soil is evaluated by using results from cyclic triaxial tests. The cyclic triaxial tests are performed on many different conditions of sample ; relative densities(50%, 60%, and 70%), initial effective confining pressures (70kPa, 100kPa, and 150kPa), and fine contents(10%, 20%, and 30%). From the result of comparing the conventional procedure with the modified detailed method, it is found that the modified detailed method tends to evaluate larger safety factor against liquefaction in the weak sand site$(FS \leq1.5)$. Therefore in this case, it is suggested that liquefaction potential should be evaluated by using the modified detailed method based on cyclic triaxial tests. It is also found that in modified detailed method based on earthquake magnitude 6.5, critical depth where liquefaction can be generated is around 15m from the ground surface.

• Journal of the Korean Geotechnical Society
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• v.35 no.3
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• pp.37-46
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• 2019

Recently, the use of CPT-based liquefaction assessment method has increased by providing more accurate results than other field tests. In CPT-based liquefaction evaluation, various soil properties are predicted and they are used for liquefaction potential assessment. In particular, fines content is one of the important input parameters in CPT-based liquefaction assessment, so it is very important to use correct prediction model and to make quantitative evaluation of estimating variability of fines content. In this study, the error evaluation of existing models for prediction of fines content through CPT was performed, and the most suitable model was selected for Pohang area, where the liquefaction phenomenon was observed in the 2017. In addition, the inherent variability of soil was analyzed, and the estimating variability of fines content was evaluated quantitatively considering the inherent variability of soil, measurement error of CPT and transformation uncertainty of selected model.

• Journal of the Korean Geotechnical Society
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• v.36 no.10
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• pp.57-71
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• 2020

Liquefaction-induced sand boils were observed during the Pohang earthquake (Moment magnitude, 5.4) on November 15, 2017, specifically in the region of agricultural fields and park areas near the epicenter. This was recorded as the first observed liquefaction phenomenon in Korea. This paper analyzes liquefaction potentials at the key sites at Pohang area. The simplified methods and current design standard were used to evaluate the occurrence of liquefaction. The seismic demand was estimated based on the NGA-WEST2 ground motion prediction equations (GMPEs). The liquefaction resistance of the ground was determined using the in-situ tests: standard penetration test (SPT) and cone penetration test (CPT). The liquefaction potentials were quantified by liquefaction potential index (LPI), which were compared with those from the previous studies.