• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.4
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• pp.1-13
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• 2009

Liquefaction is a significant threat to structures on loose saturated sandy soil deposits in the event of an earthquake, and can often cause catastrophic damage, economic loss, and loss of life. Nevertheless, the Korean peninsula has for a long time been recognized as a safe region with respect to the hazard of liquefaction, as the peninsula is located in a moderate seismicity region, and there have been no reports of liquefaction, with the exception of references in some historical documents. However, some earthquakes that have recently occurred in different parts of the world have led to liquefaction in non-plastic silty soils, a soil type that can be found in many of the western coastal areas of Korea. In this study, we first present procedures for evaluating the liquefaction potential, and calculate the liquefaction potential index (LPI) distribution at two western coastal sites using both piezocone penetration test (CPTu) data and standard penetration test (SPT) data. The LPI is computed by integrating liquefaction potential over a depth of 20m, and provides an estimate of liquefaction-related surface damage. In addition, we compared the LPI values obtained from CPTu and SPT, respectively. Our research found that the CRR values from CPTu were lower than those from the SPT, particularly in the range between 40 and 120 for the corrected tip resistance, (qc1N)CS, from the CPTu, or in the range of CRR less than 0.23, resulting in relatively high LPI values. Moreover, it was observed that the differences in the CRR between the two methods were relatively higher for soils with high fine contents.

• Journal of the Korean GEO-environmental Society
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• v.21 no.1
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• pp.13-19
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• 2020

Recently, as the number of earthquakes increases in the Korean Peninsula and surrounding area, the importance of earthquake countermeasures and seismic design has been increasing. As a result, interest and concerns about liquefaction, which is one of the problems that concern the earthquake, are increasing. There are various methods that can assess the possibility of liquefaction by using geotechnical information for specific ground. However, direct comparisons of each method are not yet available. In this study, the two methods using the SPT-N value and the shear wave velocity among the methods for estimating the Cyclic Resistance Ratio (CRR) value required for the simplified liquefaction assessment method were compared. And the correction of the ground information required to use the two methods respectively was compared. As a result, more accurate evaluation results were obtained when the CRR value is calculated using the SPT-N values.

• Journal of the Korean GEO-environmental Society
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• v.23 no.5
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• pp.5-13
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• 2022

In this study, dynamic characteristics and liquefaction resistance characteristics of silica sand which is used to simulate sandy layer were conducted using the cyclic triaxial test according to the relative density difference. The difference in liquefaction resistance with the relative density was confirmed through the test results, which the relative density conditions were changed to 40%, 60%, and 80%, and the cyclic resistance ratio (CRR) curve of the silica sand was obtained. In addition, in order to examine the validity of the liquefaction resistance ratio (CRR) curve, artificial silica sand ground was created, and liquefaction potential was evaluated through the simple assessment method and the detailed assessment method, and the safety factors of each were compared.

• Therapeutic Science for Rehabilitation
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• v.9 no.4
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• pp.69-81
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• 2020

Objective : The purpose of this study was to develop a Yonsei dual task cognitive screening test (Y-DuCog) for the elderly. Methods : The reliability and validity test of Y-DuCog (Yonsei Dual Task Cognitive Screening Test) was developed by 229 elderly people aged over 60 years from community organizations at Gyeonggi-do and Chungcheong-do from May 2019 to August 2019. In addition, the criteria for classifying elderly with cognitive impairment were presented. Results : The correlation analysis between MMSE-K, MoCA-K and Y-DuCog were a correlation between the DTE and CRR of Y-DuCog. As a result of internal consistency, Cronbach's-α values of DTE and CRR showed .848 (p<.01) and .916 (p<.01), respectively. The test-retest reliability was high. The screening point showed 88.7% sensitivity and 83.5% specificity at 31.76 seconds in total DTE, and 84.5% sensitivity and 76.6% specificity at 0.38 in total dual-task CRR. Conclusion : This study verified the reliability and validity of Y-DuCog. It was found that the level of education was not a barrier to the undertaking of this test. Furthermore, the test could be performed easily and quickly. It is also expected to be used to evaluate the effectiveness of cognitive function assessment and intervention methods in the elderly.

• Journal of the Korean GEO-environmental Society
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• v.21 no.6
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• pp.5-11
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• 2020

Recently, due to the liquefaction caused by earthquakes in Pohang and surrounding areas, the importance of researches on the liquefaction assessment has increased. The possibility of liquefaction can be assessed using the geotechnical information. The cyclic resistance ratio (CRR) value used in the assessment of liquefaction can be determined by using the SPT-N values or shear wave velocity, V_s value. A study was conducted to compare the accuracy of the liquefaction assessment using these two types of geotechnical information, and concluded that the results using SPT-N values are more accurate than those using V_s values. The previous study speculated that the used V_s value was measured at a depth of 12 m uniformly without considering the critical depth of liquefaction. Therefore, 10 empirical equations that convert SPT-N values measured at critical depth of liquefaction into V_s values to confirm the validity of geotechnical information measured at 12 m points uniformly are used to assess the liquefaction possibility and the results were compared with the actual liquefaction results to confirm the accuracy. As a result, 7 out of 10 cases considering critical depth for liquefaction show higher accuracy than those not considered.

• 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.

• Journal of the Korean Geotechnical Society
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• v.36 no.6
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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.