強震往往會造成基礎和結構物的破壞以及人員的傷亡。從大地地震工程的觀點，在強烈地震侵襲下，一個經常會發生的現象就是土壤液化。大家一致同意的觀點是液化容易發生於均勻的鬆砂土層。實際上，砂土層有可能含有粉土層；在這具有更小的滲透係數的粉土層底面，在大震時會產生具有高孔隙水壓的水膜，需要長時間才能消散完畢，是許多在地震動停止一段時間後才發生破壞的原因。 本研究利用三維非線性有效應力有限元素法分析土層的受震反應。首先以離心機試驗的結果進行驗證，然後再以九個數值分析模式進行參數分析，以瞭解含粉土層之砂土層的液化行為與在該土層內使用碎石樁以防止液化的機制。 使用碎石樁可以延緩及降低超額孔隙水壓的上升，但是在某些情況下，還是無法避免液化的產生。一般而言，碎石樁的使用可以提高土層的勁度，因而降低了地表沉陷，其值隨碎石樁面積的增加而增加。對於含粉土層之砂土層而言，粉土層的存在會降低液化區的範圍以及地表沉陷，但是在粉土層的底部會產生具有高孔隙水壓的水膜，且須要長時間才能消散完畢。隨著粉土層越多，使用碎石樁的有效性會降低。 Strong earthquakes can cause serious damage to the failure of foundations and structures, which may result in loss of lives. From the geotechnical point of view, for a large earthquake one of the frequently occurred phenomenon is known as liquefaction. The common consensus about this phenomenon is that liquefaction may easily occur in a uniform loose sandy soil stratum. In reality, the presence of intralayers of silt may be found in the field. The smaller permeability of these silt layers may develop a water film at its bottom with a high pore water pressure, leading to failure of ground even long after the earthquake shaking stopped. In this study, the seismic responses of sandy soil stratum with silt layers were obtained by using nonlinear 3D effective stress finite element program. Verification and validation of the program was done first by comparing with centrifuge test results which are in good agreement. The parametric studies using nine numerical models were then conducted to investigate the behavior of liquefiable sand-silt stratum under strong earthquakes and to gain a better understanding of the mechanism of stone columns as a countermeasure in a liquefiable sand-silt stratum. The use of stone columns can delay and reduce the accumulation of excessive pore water pressure; although in some cases liquefaction cannot be avoided. The stiffening benefit from stone columns also reduces the ground settlement which is in parallel with the area of treatment; but the effectiveness of stone columns decreases as the more intralayers of silt are introduced to the stratum. The presence of intralayers of silt will reduce the extent of liquefaction and significantly reduce the ground settlement; however, the large pore water pressure beneath each silt layer forms the water film which requires longer time to dissipate.
