한국지반공학회논문집 (Journal of the Korean Geotechnical Society)

  • 제35권7호
  • /
  • Pages.15-27
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  • 2019
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  • 1229-2427(pISSN)
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  • 2288-646X(eISSN)
한국지반공학회 (Korean Geotechnical Society)
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2차원 유효응력 해석에 의한 지진시 포항 안벽구조물의 변형 사례 분석

A Case Study on Earthquake-induced Deformation of Quay Wall and Backfill in Pohang by 2D-Effective Stress Analysis

  • 투고 : 2019.03.22
  • 심사 : 2019.06.01
  • 발행 : 2019.07.31
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초록

본 연구는 2017년 11월 15일에 발생한 규모 5.4의 포항지진을 대상으로 영일만항 안벽 및 배면에서 발생한 피해의 메커니즘을 규명하는 것이 목적이다. 현장조사 등에 의해 영일만항은 케이슨이 5cm~15cm 정도의 수평변위가 발생하였고, 뒤채움 지반에서는 10cm 이상의 침하가 발생하였다. 이에 대한 원인을 규명하기 위해 2차원 유효응력해석을 수행하였다. 입력 지진하중은 포항구항의 기반암에서 계측된 지진가속도($3.25m/s^2$)를 이용하였다. 수치해석 결과 배후지의 뒤채움 지반내 국부적으로 과잉간극수압이 증가하여 유효응력이 감소한 것으로 밝혀졌다. 이로 인해 케이슨의 경우 수평방향으로 약 14cm의 변위가 발생하였고, 3cm 정도 침하하였다. 뒤채움 지반의 경우 6cm~9cm 정도 침하한 것으로 나타났다. 이는 현장조사와도 유사한 결과임이 밝혀졌다. 또한, 뒤채움 지반내 유효응력 경로 및 응력-변형률 거동으로부터 반복적 하중에 의해 지반이 Mohr-Coulomb의 파괴선에 근접하는 것으로 나타났고, 이는 과잉간극수압의 증가에 따른 유효응력의 소실에 의한 지지력의 감소로 판단된다.

The purpose of this study is to investigate the mechanism about damages occurring at quay wall and backfill in Youngilman Port during Pohang earthquake (M5.4) on November 15, 2017. In the field investigation, the horizontal displacement of the caisson occurred between 5 cm and 15 cm, and the settlement at backfill occurred higher than 10 cm. 2D-effective Stress Analysis was performed to clarify the mechanism for the damage. The input earthquake motion used acceleration ($3.25m/s^2$) measured at bedrock of Pohang habor. Based on a numerical analysis, it was found that the effective stress decreased due to the increase of excess pore pressure in the backfill ground and the horizontal displacement of the caisson occurred by about 14 cm, and the settlement occurred by about 3 cm. In backfill, the settlements occurred between 6 cm and 9 cm. This is similar to field investigation results. Also, it was found that the backfill soil was close to the Mohr-Coulomb failure line due to the cyclic loading from the effective stress path and the stress-strain behavior. It may be related to decreasing of bearing capacity induced by the reduction of effective stress caused by the increase of the excess pore water pressure.

키워드

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Fig. 1. Damage of coastal structure by liquefaction (Sugano et al., 2014)

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Fig. 2. Youngilman Port

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Fig. 3. Damages to Youngilman habor during earthquake

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Fig. 4. Representive cross-sectional plan

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Fig. 5. Acceleration station during Pohang earthquake

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Fig. 6. Acceleration of Pohang Earthquake measurement

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Fig. 7. Schematic diagram for multiple simple shear mechanism model (Iai, 1992a)

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Fig. 8. Schematic diagram for liquefaction front, state variable (S) and shear stress ratio (Iai et al., 1992a, 1992b)

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Fig. 9. Mesh for dynamic analysis

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Fig. 10. grain-size distribution curve at Youngilman (Mun, 2018)

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Fig. 11. Responded Accelerations

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Fig. 12. Distribution of excess pore water pressure ratio

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Fig. 13. Excess pore water pressure ratio

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Fig. 14. Displacement of caisson and backfill ground

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Fig. 15. Shear stress-strain at E1

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Fig. 16. Shear stress-strain at E4

Table 1. Soil parameters for the 2-D effective stress analysis

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Table 2. Parameters of the excess pore water pressure generation model

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피인용 문헌

  1. Assessment of Pohang Earthquake-Induced Liquefaction at Youngil-Man Port Using the UBCSAND2 Model vol.10, pp.16, 2019, https://doi.org/10.3390/app10165424