서해안 사질토지반의 지진시 액상화 예측

Evaluation of Liquefaction Potential for Marine Silty Sand Deposits during Earthquake

서해안 사질토매립지반을 대상으로 지진응답해석 및 반복삼축압축시험 결과를 통하여 지진 및 예측방법에 따른 액상화특성에 대하여 검토하였다. 지수응답해석 결과, 입력지진과 지반특성에 따라 지표면에 도달하는 최대가속도의 크기가 다르게 나타남을 알았으며 간역예측법으로 해안매립지반의 액상화 평가시 적용 가능한 지진계수를 제시하였다. N치가 작고 느슨한 상부층에 대한 액상화강도는 반복삼축압축시험 결과에 비하여 Seed법에 의한 결과가 작게 나타났고 Iwasaki 방법과 S파속도 이용법은 크거나 유사한 결과를 얻었다. 또한 간역예측법들은 상세법에 비해 액상화 가능성을 과대 평가하는 경향이 있었으며 액상화 한계심도(안전율 1일때)는 입력가속도(0.1g-0.2g)에 따라 7m-14m정도로 추정되었다.

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.