| Summary: | 碩士 === 國立中央大學 === 土木工程研究所 === 92 === ABSTRACT
During earthquake, foundation soils liquefaction will cause settlement, lateral spreading and crest crack of an embankment. Recently, dynamic effective stress methods have been developed to simulate complex -liquefaction deformation behavior of an embankment. However, due to the difficulties in obtaining the relevant soil parameters and computing effort. it was recommended to establish a simplified liquefaction deformation method for use in engineering practice. Based on softening strength parameters of foundation sandy soil to simulate the liquefaction effect, this study uses 2D explicit difference program FLAC to analyze statically the post-liquefaction behavior of an embankment. The numerical results seem to be roughly consistent with the results of the dynamic centrifuge experiments. Moreover, the liquefaction-induced settlement is influenced by foundation soil types, embankment height and river topography. After the investigation of past-liquefaction deformation behavior, the effectiveness of three countermeasures is evaluated for use in preventing liquefaction of the foundation soils. Numerical results show that the use of jet grouted soilcrete at both toes of the embankment is most efficient in confining liquefied foundation soil and in reducing the post-liquefaction deformation of embankment; the effectiveness of deep mixing method is also great; however, the sheet piles can not efficiently confine foundation soil without a high-tension tie rod. In the proposed methodology, the undrained strength of all liquefiable soils was softening to the same degree; however the softening degree due to liquefaction is dependent on initial static shear stress ratio of foundation soil. This study shows that the ratio is influenced by the geometry shape of embankment and strength parameters of foundation soil.
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