원심모형시험을 이용한 케이슨 안벽의 지진시 거동에 대한 수치해석 검증

Verification of the Numerical Analysis on Caisson Quay Wall Behavior Under Seismic Loading Using Centrifuge Test

Abstract

본 논문에서는 항만구조물의 성능기반 내진설계 도입을 위해서 액상화를 포함하는 비선형 유효응력해석기법의 검증을 실시하였다. 중력식 케이슨안벽의 지진시 거동에 대해서 수치해석의 결과는 동적원심모형시험의 결과와 원형스케일로 직접 검증되었다. 중력식 안벽의 모형은 강성토조내에 지진시 과잉간극수압의 증가가 발생하는 포화 사질토 지반위에 조성되었으며, 원심가속도 60g하에서 높이 10m, 폭 6m의 케이슨 안벽을 묘사할 수 있다. 원심모형시험의 원형스케일과 동일하게 2차원 평면 변형율 조건하에서 비선형 유효응력 수치해석 모델을 구성하였다. 지반의 비선형 거동모델과 함께 Byrne의 액상화 모델을 사용하였으며, 경계요소를 적용하여 안벽과 지반의 분리거동을 묘사하였다. 검증결과, 안벽의 잔류변위를 포함하여 지반 및 안벽의 수평가속도와 안벽기초 하부 사질토 지반의 과잉간극수압 증가양상 모두 유사한 결과를 나타내었다.

In this study, verification of the nonlinear effective stress analysis is performed for introducing performance based earthquake resistance design of port and harbor structures. Seismic response of gravitational caisson quay wall in numerical analysis is compared directly with dynamic centrifuge test results in prototype scale. Inside of the rigid box, model of the gravitational quay wall is placed above the saturated sand layer which can show the increase of excess pore water pressure. The model represents caisson quay wall with a height of 10 m, width of 6 m under centrifugal acceleration of 60 g. The numerical model is made in the same dimension with the prototype scale of the test in two dimensional plane strain condition. Byrne's liquefaction model is adopted together with a nonlinear constitutive model. Interface element is used for sliding and tensional separation between quay wall and the adjacent soils. Verification results show good agreement for permanent displacement of the quay wall, horizontal acceleration at quay wall and soil layer, and excess pore water pressure increment beneath the quay wall foundation.

Fig. 1. Typical failure mechanism of caisson quay wall and quay crane after earthquake

Fig. 2. Experimental model setup for dynamic centrifuge test

Fig. 3. Measurement system installation profile (Model scale, Dimensions in cm)

Fig. 4. Dimensions of the numerical model

Fig. 5. Interface behavior used in the numerical analysis

Fig. 6. Shear modulus and damping ratio fitting results of dry silica sand

Fig. 7. Updated the maximum shear modulus distribution after static equilibrium (Unit, Pa)

Fig. 8. Shear wave velocity of silica sand with confining pressure

Fig. 9. Incremental Volumetric Strain Curves (Martin et al., 1975)

Fig. 10. Changes of volumetric strain as increasing number of cycles (Itasca, 2013)

Fig. 11. Diagrammatic cross section of particulate group showing packing changes that occur during cyclic loading (Youd, 1977)

Fig. 12. Forces acting on a typical waterfront retaining wall (Bellezza et al., 2009)

Fig. 13. Step by step analysis following construction stage

Fig. 14. Comparison of the horizontal acceleration history for the major points

Fig. 15. Comparison of the porewater pressure history for the major points

Fig. 16. Comparison of the permanent displacement of the quay wall

Table 1. Input parameters for the numerical analysis

Table 2. Engineering properties of the silica sands

Table 3. Mathematical fitting function models for nonlinear cyclic behavior of soil in FLAC analysis

Table 4. Engineering parameters of silica sand