饱和砂土在地震荷载的作用下往往会产生液化变形，包括竖向震陷和侧向扩展。砂土由于液化的作用，其渗透系数会发生改变，而目前描述砂土液化变形的本构模型均采用常量渗透系数，这是造成自由场地的震陷数值模拟结果低于试验观测值的重要原因之一。利用开源有限元平台OpenSees对饱和砂土的自由场地震陷进行模拟分析，对比离心机模型试验，分析了渗透系数对饱和砂土液化震陷的影响。为进一步提高数值模拟的准确性，采用了适合于动力分析及液化模拟的边界面模型。与固定渗透系数模型相比，最终提出的变渗透系数模型允许液化状态的渗透系数升高为初始值的数倍，该模型模拟结果较好，可以作为从渗透模型角度提高数值模拟精度的近似考虑。通过一系列的模拟和分析发现，采用合理的变渗透系数模型，可在一定程度上提高砂土自由场地地震液化震陷的数值模拟精度。

Seismic loading may result in liquefaction-induced deformation in saturated sand, including seismic settlement and lateral spreading. The permeability coefficient of sand may change after liquefaction. Variation of the permeability coefficient has not been included in the existing models. This is one of the main reasons for the underestimation of the seismic settlement in the numerical simulations comparing to the experimental observations. To analyze the effect of the variation of permeability coefficient on the liquefaction-induced settlement, the settlement in free-field condition is simulated using OpenSees platform, and compared with centrifuge experiments. The proposed model with variable permeability coefficient allows the maximum permeability coefficient during the liquefaction several times of its initial value. Compared with the model with fixed permeability, the proposed model properly describe the evolution of settlement and excess pore water pressure, and improve the accuracy of the settlement prediction in the numerical simulation. The results show that the adopted variable permeability model is capable to simulate the behavior of the sand in the free-field condition under seismic loading with an acceptable accuracy.