• 한국지반공학회논문집
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• 제36권4호
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• pp.17-30
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• 2020

본 연구의 목적은 2017년 포항지진 시 액상화가 관측되었거나 액상화 가능성이 높은 부지 5곳에 대하여, 국내에서 통상적으로 적용해 왔던 액상화 평가 기준과 최근 개정된 평가 기준을 적용하여 액상화 평가를 실시하고, 이러한 이론적인 액상화 평가 결과와 대상 부지에서의 실제 액상화 발현여부를 비교·검토함으로써, 개정된 액상화 평가 기준의 타당성을 검토하는 데에 있다. 액상화 평가를 위한 해석지진은 기존 국내에서 통상적으로 사용해 온 지진파와 포항 실지진파를 사용하였고, 해석지진의 최대지반가속도 크기는 0.097g~0.2713g 범위의 값을 적용하였다. 해석결과로부터, 기존 국내에서 통상적으로 적용해 왔던 구조물기초설계기준(2016)에 제시된 액상화 평가 기준의 개선점을 제시하고, 2018년에 개정된 내진설계일반에 제시된 액상화평가 기준의 기존 기준대비 개정 사항의 상대적 타당성을 평가해 보았다.

• 한국지반신소재학회논문집
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• 제23권2호
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• pp.29-42
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• 2024

2017년 포항지진으로 인해 액상화 현상에 의한 안벽구조물에 피해가 발생하였다. 액상화는 지진 시 과잉간극수압 증가로 인해 유효응력이 소실되어 발생하게 된다. 이에 따른 잔교식 안벽의 피해 발생 부분을 규명하며 액상화로 인한 피해를 분석하였다. 또한 개량지반의 경우 연암층과 강성차이로 인해 하부 Sand 층의 액상화 현상으로 인해 피해가 발생하여, 비액상화 지반으로 가정하고 추가적인 수치해석을 수행하였다. 과잉간극수압비의 증가에 영향을 주는 요인으로는 지반의 상대밀도 및 입력 지진가속도의 크기 등 여러 가지 원인이 있다. 따라서 본 연구는 입력가속도의 크기를 증가시켜 Case 1~3에 대해 수치해석을 수행하였고, 개량지반의 경우 하부 Sand층의 액상화 현상으로 인한 피해가 발생하여 비액상화지반으로 가정하여 분석을 수행하였다. 결과적으로, 개량지반은 하부 액상화지반이 있을 경우 추가적인 보강이 필요하며, 잔교식 안벽 말뚝의 수평변위가 약 2배 감소하는 현상이 나타났다.

• 한국농공학회지
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• 제35권2호
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• pp.43-56
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• 1993

The laboratory tests are performed on how the liquefaction potential of the sea dike structures on the saturated sand or silty sand seabed could be affected due to earthquake before and after construction results are given as follows ; 1. Earthquake damages to sea dike structures consist of lateral deformation, settlement, minor abnormality of the structures and differential settlement of embankments, etc. It is known that severe disasters due to this type of damages are not much documented. Because of its high relative cost of the preventive measures against this type of damages, the designing engineer has much freedom for the play of judgement and ingenuity in the selection of the construction methods, that is, by comparing the cost of the preventive design cost at a design stage to reconstruction cost after minor failure. 2. The factors controlling the liquefaction potential of the hydraulic fill structure are magnitude of earthquake(max. surface velocity), N-value(relative density), gradation, consistency(plastic limit), classification of soil(G & vs), ground water level, compaction method, volumetric shear stress and strain, effective confining stress, and primary consolidation. 3. The probability of liquefaction can be evaluated by the simple method based on SPT and CPT test results or the precise method based on laboratory test results. For sandy or silty sand seabed of the concerned area of this study, it is said that evaluation of liquefaction potential can be done by the one-dimensional analysis using some geotechnical parameters of soil such as Ip, Υt' gradation, N-value, OCR and classification of soils. 4. Based on above mentioned analysis, safety factor of liquefaction potential on the sea bed at the given site is Fs =0.84 when M = 5.23 or amax= 0.12g. With sea dike structures H = 42.5m and 35.5m on the same site Fs= 3.M~2.08 and Fs = 1.74~1.31 are obtained, respectively. local liquefaction can be expected at the toe of the sea dike constructed with hydraulic fill because of lack of constrained effective stress of the area.

• 한국지반공학회지:지반
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• 제14권2호
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• pp.9-20
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• 1998

지진에 의한 지반의 액상화 현상으로 인하여 지하에 매설된 생활관거가 파괴될 가능성은 대단히 높다. 만일 지진이 발생하는 즉시 지반의 액상화 가능성을 판단할 수 있다면 관거가 파괴됨으로 인한 피해를 최소한으로 감소시킬 수 있다. 액상화 현상이 지반에 발생하는 동시에 이를 판별하기 위해서는 지표에서 진동의 이력을 측정함과 동시에 해석함으로써 가능하다. 본 논문에 서는 지표에서 측정된 가속도 기록을 통하여 지반의 액상화 가능성과 액상화된 지반의 두께를 평가하는 방법을 제시하고자 한다. 이를 위하여 실제로 측정된 지진 기록을 해석하고, 또한 진동대시험이 실시되었다. 이 결과 액상화 지반의 판별과 액상화된 지반의 두께는 지반 최대 가속도와 스펙트럼 강도로 결정할 수 있음이 증명되었다.

• Geomechanics and Engineering
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• 제37권4호
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• pp.395-418
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• 2024

The epicentral region of earthquakes is typically where liquefaction-related damage takes place. To determine the maximum distance, such as maximum epicentral distance (R_e), maximum fault distance (R_f), or maximum hypocentral distance (R_h), at which an earthquake can inflict damage, given its magnitude, this study, using a recently updated global liquefaction database, multiple ML models are built to predict the limiting distances (R_e, R_f, or R_h) required for an earthquake of a given magnitude to cause damage. Four machine learning models LSTM (Long Short-Term Memory), BiLSTM (Bidirectional Long Short-Term Memory), CNN (Convolutional Neural Network), and XGB (Extreme Gradient Boosting) are developed using the Python programming language. All four proposed ML models performed better than empirical models for limiting distance assessment. Among these models, the XGB model outperformed all the models. In order to determine how well the suggested models can predict limiting distances, a number of statistical parameters have been studied. To compare the accuracy of the proposed models, rank analysis, error matrix, and Taylor diagram have been developed. The ML models proposed in this paper are more robust than other current models and may be used to assess the minimal energy of a liquefaction disaster caused by an earthquake or to estimate the maximum distance of a liquefied site provided an earthquake in rapid disaster mapping.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.1246-1249
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• 2009

Liquefaction hazard caused by earthquake is the damage in a wide range. Until now, liquefaction hazard potential at a small area or most structure in Korea was assessed by modified Seed & Idriss method. However, it has been known that this method is not proper for metropolitan area due to a lot of time and data to perform the related ground response analyses such as Shake program. For these reasons, the current method has been used facilities or structures, not metropolitan area. In this study, several contents in seismic design of Eurocode and Korean seismic design standard for Port and Harbor were introduced and applied for assessing the liquefaction potential and mapping the liquefaction hazard by LPI(Liquefaction Potential Index). Finally, Ulsan metropolitan city was practically drawn in two dimensional space.

• 한국농공학회지
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• 제33권3호
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• pp.51-62
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• 1991

A comprehensive laboratory investigation of the liquefaction characteristics of Jumunjin standard sand. Seoul sand and Hongsung sand was peformed by the undrained cyclic triaxial compression test under different relative densities, confining pressures and cyclic deviator stresses. The results obtained are as follows ; 1. Liquefaction potential was dominated by the stress ratio at a given number of cycle. That is, the number of cycle required to cause initial liquefaction became samller as the stress ratio increased. 2. Liquefaction potential of a sand was infliuenced by initial relative density or void ratio. Under a given relative density. liquefaction potential of Jumunjin standard sand and Seoul sand was smaller than that of Hongsung sand. 3. The pore pressure ratio of Hongsung sand was the smallest three under a given relative density and stress ratio, and it showed higher value when the cyclic stress and the shear strain were high. 4. An excessive pore pressure ratio not found when initial shear was smaller than 0.01%, and the pore pressure ratio started to increase when initial shear became greater than 0.01%. 5. Soil texture is an important factor to cause liquefaction, and liquefaction potential decreased a the mean grain size decreased. however the sand having fine grain such as Hongsung sand showed somewhat higher liquefaction potential. 6. Based on the analysis of the specimens whose number of the cycles to cause liquefaction was 8~12, it was found that the relationship between density and stress ratio was linear. The curves for Hongsung sand was steeper than the other. 7. From the above results and the method suggested by Seed-Idriss, it may be considered that the damages by Hongsung earthquake was not directly caused by liquefaction.

• Geosciences Journal
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• 제22권6호
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• pp.871-880
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• 2018

During and shortly after the 2017 Pohang Earthquake ($M_w$ 5.4), sand blows were observed around the epicenter for the first time since the beginning of instrumental seismic recording in South Korea. We carried out field surveys plus satellite and drone imagery analyses, resulting in observation of approximately 600 sand blows on Quaternary sediment cover in this area. Most were observed within 3 km of the epicenter, with the farthest being 15 km away. In order to investigate the ground's susceptibility to liquefaction, we conducted a trench study of a 30 m-long sand blow in a rice field 1 km from the earthquake epicenter. The physical characteristics of the liquified sediments (grain size, impermeable barriers, saturation, and low overburden pressure) closely matched the optimum ground conditions for liquefaction. Additionally, we found a series of soft sediment deformation structures (SSDSs) within the trench walls, such as load structures and water-escaped structures. The latter were vertically connected to sand blows on the surface, reflecting seismogenic liquefaction involving subsurface deformation during sand blow formation. This genetic linkage suggests that SSDS research would be useful for identifying prehistoric damage-inducing earthquakes ($M_w$ > 5.0) in South Korea because SSDSs have a lower formation threshold and higher preservational potential than geomorphic markers formed by surface ruptures. Thus, future combined studies of Quaternary surface faults and SSDSs are required to provide reliable paleoseismological information in Korea.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.722-729
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• 2004

The horizontal movement of sloping ground due to flow liquefaction has caused many pile foundations to fail, especially those in ports and harbor structures. In this study, a virtual case is assumed in which flow liquefaction is induced by earthquake loads in a fully saturated infinite sand slope with a single pile installation. Under the assumption that the movement of liquefied ground is viscous fluid flow, the influence of ground movement due to flow liquefaction on the pile behavior was analyzed. Since the liquefied soil is assumed as a viscous fluid, its viscosity must be evaluated, and the viscosity was estimated by the dropping ball method ,md the pulling bar method. Finally, the influence of the flow of liquefied soil on a single pile installed in an infinite slope was analyzed by a numerical method.

• 한국지반환경공학회 논문집
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• 제14권6호
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• pp.13-19
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• 2013

본 연구에서는 액상화 평가 대상지반을 선정하여 미국, 일본 등 액상화 발생지역에 적용한 사례가 있는 에너지를 기반으로 하는 Arias intensity 액상화 평가법을 적용하고, 적용성을 검토하기 위하여 기존의 원위치시험을 통한 액상화 간편예측법을 수행하여 평가결과를 비교하였다. 대상지반에 대한 액상화 평가결과, Hachinohe 지진과 Ofunato 지진의 실지진기록을 이용한 Arias Intensity 안전율은 간편예측 안전율과 유사하게 산정되었으며, 설계응답스펙트럼으로부터 작성된 인공지진의 경우 Arias Intensity 안전율은 간편예측 안전율과 비교하여 다소 차이가 나타났다. 액상화를 발생시키는 전단응력비와 발생강도는 응력과 에너지라는 서로 다른 개념으로 산정되지만, 간편예측법의 전단저항응력비와 Arias Intensity의 저항강도는 실지진에 따른 액상화 발생지역을 대상으로 한 표준관입시험 등 경험적 도표를 사용한다는 점에서 Hachinohe 지진과 Ofunato 지진의 경우 Arias Intensity 평가법과 응력개념의 간편예측법 사이에 비슷한 결과가 나타난 것으로 판단된다. 따라서, 에너지를 기반으로 하는 Arias Intensity 액상화 평가법은 응력개념의 간편예측법에서 고려하지 않은 실지진 기록에 대한 가속도, 지속시간, 진폭 등의 지진특성으로 야기되는 지반의 동적변화를 표현할 수 있음을 확인할 수 있었다.