Journal of the Korean Geotechnical Society (한국지반공학회논문집)

Korean Geotechnical Society (한국지반공학회)
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A Quantitative Physical Parameter for Detection of Ultimate Failure State of Soil Using CEL Method in Finite Element Analysis

CEL 기법을 이용한 유한 요소 해석에서 지반의 극한 파괴 상태 감지를 위한 정량적 물리량 기준

  • Kim, Seongmin (Dept. of Civil Engrg., Kyung Hee Univ.) ;
  • Lee, Ju-Hyung (Geotechnical Engrg. Research Institute, Korea Institute of Civil Engrg. and Building Technology) ;
  • Jung, Young-Hoon (Dept. of Civil Engrg., Kyung Hee Univ.)
  • 김성민 (경희대학교 사회기반시스템공학과) ;
  • 이주형 (한국건설기술연구원 지반연구소) ;
  • 정영훈 (경희대학교 사회기반시스템공학과)
  • Received : 2018.10.08
  • Accepted : 2018.11.15
  • Published : 2018.12.31
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Abstract

In order to use the limit equilibrium theory, it is necessary to find a slip line under the ultimate failure condition. The strength reduction method using the Lagrangian finite element method defines the ultimate failure state at a time when the numerical solution cannot converge within the certain number of the iteration. When the coupled Eulerian-Lagrangian (CEL) method is used, however, such definition is inappropriate because the numerical solution of the CEL method can converge even under the ultimate failure condition. In this study, an objective condition designating the ultimate failure state in the finite element analysis adopting the CEL method was proposed. In the problem of the bearing capacity of the undrained soft ground subjected to the strip footing loading, we found that the rate of the plastic dissipated energy is highly sensitive at the load of the theoretical limit of the ultimate failure state.

한계평형법 이론들을 사용하기 위해서는 극한 파괴 상태에서 나타나는 파괴 전단면을 찾아야 한다. 강도 감소법에서는 유한요소해석의 수치해가 일정 반복 횟수 이내에 수렴하지 못하는 시점을 극한 파괴 상태로 정의한다. 하지만 Coupled Eulerian-Lagrangian (CEL)기법을 유한요소해석에서 사용하면 극한 파괴 상태에 도달하여도 수치해의 비수렴 상황이 발생하지 않으므로 이러한 정의는 사용하기 어렵다. 본 연구에서는 CEL 기법을 이용한 유한요소해석에서 지반의 극한 파괴 상태를 감지할 수 있는 객관적인 물리량 기준을 제시하였다. 비배수 조건의 연약지반이 연속기초 하중을 받는 경우 극한 파괴 상태에 해당하는 이론적 하중에서 소성 소산 에너지의 변화속도가 민감하게 변화함을 찾을 수 있었다.

Keywords

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Fig. 1. Geometry and boundary conditions of strip footing model

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Fig. 2. Geometry and boundary conditions of CEL model

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Fig. 3. Reaction force-time curve of the strip footing

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Fig. 4. Variations of observed parameters during loading

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Fig. 4. Variations of observed parameters during loading (Continued)

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Fig. 5. Rate variations of observed parameters during loading

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Fig. 5. Rate variations of observed parameters during loading (Continued)

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Fig. 6. Finite element models along the analysis conditions

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Fig. 7. Reaction force-time curves and plastic dissipated energy rates along the analysis conditions

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Fig. 8. Failure slip lines along the analysis conditions

Table 1. Material properties of strip footing model

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Table 2. Analysis conditions of the strip footing model

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