橋樑通常是透過樁基礎穿越軟弱土層，將荷載傳遞到可承載的深層土層。過去許多地震災害的報告中，都可看到橋樑之樁基礎受土壤液化而導致損壞的情況。本研究的目的是探討橋樑樁基礎在不規則液化土層中之受震反應。 本研究中，不規則液化土層中基樁的受震反應分析是採用三維非線性有效應力有限元素法。非線性土壤的行為以依 Mohr-Coulomb破壞準則的帽蓋模式模擬，而孔隙水壓則採用Pacheco模式。參數研究方面採用三方向的加速度歷時作為輸入震源，針對側邊岩盤坡度的變化、局部岩盤凸起與二種樁帽與基樁的銜接方式來分析液化土層中的樁基礎的受震反應。 經參數分析後，發現不規則液化土層中橋樑樁基礎的受震反應(位移、剪力、軸力與彎矩)受地震的特性、基樁在群樁中的位置與不規則土層的構造的影響很大。因此，採用橋樑興建場址的地震動以及盡可能地掌握該場址的土層及岩盤構造，對於橋樑樁基礎的耐震能力的檢核是很重要的。 Pile foundations are often used to transfer loads of bridge through soft soil to stronger bearing strata at depth. In the past earthquakes, there have been many reports about damage to bridge’s pile foundations caused by soil liquefaction. The purpose of this study is to investigate the seismic responses of pile foundations of a bridge pier in a liquefiable soil stratum underlain by irregular bedrock. In this study, the effect of irregular bedrock on the seismic responses of pile is investigated using nonlinear three-dimensional effective stress finite element method. The nonlinear soil behavior is modeled using the Cap model with Mohr-Coulomb type failure line. The pore pressure model adopted is the one proposed by Pacheco. The seismic responses of pile foundations in liquefiable soil stratum were then studied for slope variation of inclined lateral rock and local intrusion of bedrock and two types of connection between pile cap and piles were considered in the analysis: fixed connection and hinge connection. Three acceleration time-histories were used as input motion. From the parametric studies, it was found that the effect of irregular bedrock on the pile responses (displacement, shear force, axial force and bending moment) depends on the characteristics of earthquake motions, location of pile within the pile group and sometimes the configuration of the irregular bedrock. Therefore, it is important to check the adequacy of pile foundation design using the earthquake motions measured at the construction site whose bedrock configuration should be determined as accurately as possible.