Journal of the Korean GEO-environmental Society (한국지반환경공학회 논문집)

Korean Geo-Environmental Society (한국지반환경공학회)
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Seismic Margin Assessment of Concrete Retaining Walls

콘크리트 옹벽의 지진여유도 평가

  • Park, Duhee (Department of Civil and Environment Engineering, Hanyang University) ;
  • Baeg, Jongmin (Department of Civil and Environment Engineering, Hanyang University) ;
  • Park, Inn-Joon (Department of Civil Engineering, Hanseo University) ;
  • Hwang, Kyeungmin (Korea Electricity Power Corporation Research Institute) ;
  • Jang, Jungbum (Korea Electricity Power Corporation Research Institute)
  • Received : 2019.05.09
  • Accepted : 2019.07.01
  • Published : 2019.07.01
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Abstract

In recent Gyeongju and Pohang earthquakes, motions that exceed the design ground motion were recorded. This has led to adjustments to the design earthquake intensity in selected design guidelines. An increment in the design intensity requires reevaluation of all associated facilities, requiring extensive time and cost. Firstly, the seismic factor of safety of built concrete retaining walls are calculated. Secondly, the seismic margin of concrete retaining walls is evaluated. The design sections of concrete walls built at power plants and available site investigation reports are utilized. Widely used pseudo-static analysis method is used to evaluate the seismic performance. It is shown that all concrete walls are safe against the adjusted design ground motion. To determine the seismic margin of concrete walls, the critical accelerations, which is defined as the acceleration that causes the seismic factor of safety to exceed the allowable value, are calculated. The critical acceleration is calculated as 0.36g~0.8g. The limit accelerations are significantly higher than the design intensity and are demonstrated to have sufficient seismic margin. Therefore, it is concluded that the concrete retaining walls do not need to be reevaluated even if the design demand is increased up to 0.3g.

최근 발생한 경주지진('16.9.12., $M_L=5.8$) 및 포항지진('17.11.15., $M_L=5.4$)에서 국내의 설계지반운동 수준을 초과하는 진동이 관측되었으며 이를 계기로 설계지반운동이 일부 내진설계지침서에서 개정되었다. 설계지반운동이 조정되면 관련된 모든 시설물의 내진성능을 재평가해야 하며 이를 위해서는 막대한 시간과 비용이 소요된다. 본 연구에서는 일차적으로 조정된 설계지반운동기준에 대한 기설된 콘크리트 옹벽의 내진성능 확보 여부를 평가하였으며 이차적으로 콘크리트 옹벽의 지진여유도를 평가하였다. 변전소 주변에 기설된 콘크리트 옹벽 단면과 지반주상도를 사용하였으며 지진에 대한 안전율은 유사정적해석법을 사용하여 계산하였다. 평가에 사용된 모든 옹벽은 조정된 설계지반운동에 대해서 충분한 성능을 확보하고 있는 것으로 나타났다. 나아가 옹벽의 지진여유도를 평가하기 위하여 기준 안전율을 만족하지 못하는 임계가속도를 계산하였다. 임계가속도는 0.36g~0.8g 범위로 설계지반운동을 크게 상회하며 콘크리트 옹벽의 지진여유도는 매우 큰 것으로 분석되었다. 따라서 추후 설계지반운동이 0.3g 이상으로 상향조정되어도 옹벽의 전면적인 재평가는 불필요할 것으로 판단된다.

Keywords

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Fig. 1. Schematic of Mononobe-Okabe method (Wagner & Sitar, 2016)

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Fig. 2. Section of concrete retaining wall

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Fig. 3. Flow chart for evaluation of the seismic performance of concrete walls

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Fig. 4. Spectrum matched acceleration time histories and 5% damped response spectra of input ground motions

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Fig. 5. Shear wave velocity profiles of wall sites

Table 1. Safety factors of concrete retaining wall (MOLIT, 2016)

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Table 2. Dimensions of inverted T-type retaining walls (h = height of wall, B = width of wall base, H = height of backfill, Df = depth of penetration)

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Table 3. Comparison of calculated PGA with KEPRI PGA

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Table 4. Calculated safety factors and critical accelerations of concrete retaining walls

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