• Title/Summary/Keyword: 액상화 평가

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A Study on the Evaluation of the Effect of the Ground Improvement of Reclaimed Land Based on Dynamic Compaction Method (동다짐 공법이 적용된 준설매립지반의 개량효과 평가에 관한 연구)

  • Kim Jong-Kook;Chae Young-Su
    • Journal of the Korean Geotechnical Society
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    • v.22 no.5
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    • pp.13-26
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    • 2006
  • The purpose of this study is to examine the method of liquifaction potential occuring at the reclaimed land in Incheon district and to compare the result obtained by the method based on the earthquake of 6.5 magnitude. In addition, the effects of ground improvement and liquifaction potential were evaluated on the basis of SPT and CPT, which have been performed before and after the compaction pilot test. As a result, we realized that the bigger the energy of dynamic compaction test was, the better effect we got. After the dynamic compaction test, as the strength of ground increased, the safe factor also increased. It was evaluated that the method of dynamic compaction improved the seismic performance. Accordingly, the method of the quality control of reclaimed land based on dynamic compaction method was presented.

Examination of Applicability of Liquefaction Potential Index to Seismic Vulnerability Evaluation of the Korean River Levees (액상화 가능 지수의 국내 하천제방 지진취약도 평가 적용성 검토)

  • Ha, Iksoo;Moon, Injong;Yun, Jungwon;Han, Jintae
    • Journal of the Korean GEO-environmental Society
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    • v.18 no.4
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    • pp.31-40
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    • 2017
  • In this study, a simple method to evaluate the seismic vulnerability of river levees was examined considering the structural characteristic of river levee, that is long, and the functional characteristic of river levee that performs temporary function against flood but is a permanent structure in the ordinary way. Considering the fact that one of the main failure modes of the levee during the earthquake are the settlement due to the strength reduction of the ground caused by the increase of the excess pore pressure in the levee body and foundation and the settlement due to liquefaction, the 2-dimensional section of the levee was regarded as the 1-dimensional section and the liquefaction potential index (LPI) for the regarded section was estimated. The estimated LPI was correlated with the seismic vulnerability of river levees. The relationship between the displacement of the levee crest caused by the earthquake and the seismic vulnerability of the levees was obtained from the results of previous researches and the correlation between the displacements of the levee crest computed by 2-dimensional dynamic coupled analyses and LPIs based on the results of 1-dimensional seismic response analyses was investigated. In connection with this correlation, as a result of examination of the correlation between LPI and the seismic vulnerability of the levee, it was concluded that the method for evaluation of the seismic vulnerability of the Korean river levee using LPI is applicable.

Evaluation of Liquefaction Potential for Marine Silty Sand Deposits during Earthquake (서해안 사질토지반의 지진시 액상화 예측)

  • 이희명;정두영
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.6 no.1
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    • pp.23-33
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    • 1994
  • Liquefaction characteristics of the reclaimed marine sand deposits is studied by means of the dynamic response analysis and the cyclic triaxial compression test. 1) From the result of the dynamic response analysis. it was found that the amplification of ground surface maximum acceleration varied with input earthquake motions and soil data, and earthquake coefficients were proposed to be applicable in evaluating liquefaction potential by simplified prediction methods. 2) For upper and soft sand deposits with small N-value, liquefaction strengths estimated by Seed and Idriss's simplified method were lower than those by the cyclic triaxial test while those by Iwasaki & Tatsuoka's or Vs-method were not lower. 3) Simplified methods were inclined to overestimate liquefaction potential in comparison with the dynamic response analysis and the cyclic triaxial compression test Allowable depths of liquefaction(safety factor 1) were estimated to be 7-14m for 0.1 -0.2g of input maximum acceleration.

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Evaluation of Liquefaction Triggering for the Pohang Area Based on SPT and CPT Tests (SPT와 CPT 지반조사결과에 기초한 포항지역 액상화 위험도 평가)

  • Kim, Yeon-Jun;Ko, Kil-Wan;Kim, Byung-Min;Park, Du-Hee;Kim, Ki-Seog;Han, Jin-Tae;Kim, Dong-Soo
    • 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.

Stiffness Degradation and Unconfined Strength of the Chemically Grouted Sand Subjected to Cyclic Shear (반복전단을 받는 고화 처리토의 강성저하와 일축압축강도)

  • Kwon, Youngcheul;Lee, Bongjik;Bae, Wooseok
    • Journal of the Korean GEO-environmental Society
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    • v.8 no.5
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    • pp.23-29
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    • 2007
  • The performance of the improved soil against liquefaction depends upon the chemical density, and it has been decided on the basis of the unconfined compressive strength of the improved soil up to date. On the other hand, several authors have proposed that the stiffness degradation could be treated as the clue for the judgment of the possibility of liquefaction. In this study, therefore, the stiffness degradation of the improved soil was estimated as the resistance against liquefaction by using the strain controlled cyclic triaxial test equipment. Based on the test results, it is concluded that the chemically treated sand can resist against the liquefaction in aspect of the reduction in effective stress and in the stiffness. Furthermore, even in the case of low chemical density, such as 2% in this study, has enough liquefaction resistance when compared with the 5~6% which often used in practical design. Considering this fact, the design of chemical density based on the unconfined strength can lead the overestimation in chemical density, and chemical density can be reduced when considering the stiffness reduction shown in this study.

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A proposed model of limit equilibrium analysis for stability assessment of underground structure in liquefied ground during earthquakes (지진 시 액상화된 지반 내 지중 구조물의 안정성 평가를 위한 한계평형해석 모델 제안)

  • Ju-Young Oh;Jaehwan Lee;Seokbue Chang
    • Journal of Korean Tunnelling and Underground Space Association
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    • v.26 no.5
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    • pp.435-448
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    • 2024
  • Liquefaction of the ground caused by earthquakes results in significant damage to underground structures such as tunnels, pipelines, manholes, and underground tanks. The uplift of underground structures due to liquefaction has been identified as a major cause of this damage. However, current design practices have not adequately considered the upward displacement of underground structures. This paper proposes an analytical solution based on the limit equilibrium method for cut-and-cover tunnels. Using this solution, a sensitivity analysis was performed on soil cover height, liquefaction depth, ground improvement, and ledge. It was confirmed that the contribution of each factor to the safety factor can be reasonably derived through changes in the safety factor. Although there are still many assumptions and uncertainties that need to be reviewed for their appropriateness, a conservative approach appears to mitigate a significant portion of these uncertainties. This study is meaningful as a stability evaluation method considering the uplift behavior characteristics of underground structures.

Occurrence of Sand Liquefaction on Static and Cyclic Loading (정적 및 동적 하중에서 모래의 액상화 발생)

  • 양재혁
    • Journal of the Korean Geotechnical Society
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    • v.17 no.6
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    • pp.235-244
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    • 2001
  • Liquefaction may be caused by sudden decrease in the soil strength under undrained conditions. This loss of soil strength is related to the development of excess pore pressures. During this study, fines content affects the maximum and minimum void ratios are investigated. The results of static and cyclic triaxial test on silty saturated sands are presented. These tests are performed to evaluate liquefaction strength and static and cyclic behavior characteristics. The samples are obtained from Saemangeum and drying on air. The main results are summarized as follows : 1) The maximum and minimum void ratio lines follow similar trends. 2) Maximum and minimum void ratios are established at 20~30% fines content. 3) As confining pressures and overconsolidation ratio are increased, the resistance to liquefaction are increased. 4) Instability friction angles are increased with increasing initial relative density. 5) The resistance to liquefaction are decreased with increasing effective stress ratio.

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Probabilistic Analysis of Liquefaction Induced Settlement Considering the Spatial Variability of Soils (지반의 공간변동성을 고려한 액상화에 의한 침하량의 확률론적 해석)

  • Bong, Tae-Ho;Kim, Byoung-Il
    • Journal of the Korean Geotechnical Society
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    • v.33 no.5
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    • pp.25-35
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    • 2017
  • Liquefaction is one of the major seismic damage, and several methods have been developed to evaluate the possibility of liquefaction. Recently, a probabilistic approach has been studied to overcome the drawback of deterministic approaches, and to consider the uncertainties of soil properties. In this study, the spatial variability of cone penetration resistance was evaluated using CPT data from three locations having different variability characteristics to perform the probabilistic analysis considering the spatial variability of soil properties. Then the random fields of cone penetration resistance considering the spatial variability of each point were generated, and a probabilistic analysis of liquefaction induced settlement was carried out through CPT-based liquefaction evaluation method. As a result, the uncertainty of soil properties can be overestimated when the spatial variability is not considered, and significant probabilistic differences can occur up to about 30% depending on the allowable settlement.

Investigation of Pohang Earthquake Liquefaction Using 1D Effective-Stress Site Response Analysis (1차원 유효응력개념의 지반응답해석을 통한 포항지진의 액상화 현상 규명)

  • Ahn, Jae-Kwang;Baek, Woo-Hyun;Choi, Jae-Soon;Kwak, Dong Youp
    • 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.

Analysis of the Characteristics of Liquidization Behavior of Sand Ground in Korea Using Repeated Triaxial Compression Test (반복삼축압축시험을 이용한 국내 모래지반의 액상화 거동 특성 비교)

  • Seo, Hyeok;Kim, Daehyeon
    • The Journal of Engineering Geology
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    • v.31 no.4
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    • pp.493-506
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    • 2021
  • Liquefaction refers to a phenomenon in which excessive pore water pressure occurs when a dynamic load such as an earthquake rapidly acts on a loose sandy soil saturated with soil, and the ground loses effective stress and becomes liquefied. The indoor repeated test for liquefaction evaluation can be confirmed through the repeated triaxial compression test and the repeated shear test. In this regard, this study tried to confirm the liquefaction resistance strength according to the relative density and particle size distribution of sand using the repeated triaxial compression test. As a result of the experiment, it was confirmed that the liquefaction resistance strength increased as the relative density increased regardless of the soil classification, and the liquefaction resistance strength according to the particle size distribution of the sand was confirmed that the liquefaction resistance strength of the SP sample close to SW was significantly higher. In addition, as a result of analyzing 30% of fine powder compared to 0% of fine powder, as the relative density increased to 40~70%, the liquefaction resistance strength decreased by 5~20%, and the domestic weathered soil ground had a fine liquefaction resistance strength compared to Jumunjin standard sand. When the minute was 10%, it was measured to be 30% or more, and when the fine particle was 30%, it was measured to be less than 50%.