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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Open Sees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。
Saturated sand tends to liquefy under seismic loads, including vertical seismic subsidence and lateral expansion. The permeability coefficient of sandy soil changes due to the liquefaction. However, constitutive models that describe the liquefaction deformation of sand are constant permeability coefficient, which is the important reason that the numerical simulation result of free fall is lower than the experimental observation one. The open-ended finite element platform Open Sees is used to simulate the free-field seismic subsidence of saturated sand. Comparing with the centrifuge model test, the influence of permeability coefficient on the liquefaction subsidence of saturated sand is analyzed. In order to further improve the accuracy of numerical simulation, a boundary model suitable for dynamic analysis and liquefaction simulation is adopted. Compared with the fixed coefficient of permeability model, the proposed permeability coefficient model finally allows the permeability coefficient of the liquefied state to increase several times as much as the initial value. The result of this model is good and can be used as an approximation to improve numerical simulation accuracy from the perspective of the permeability model . Through a series of simulations and analyzes, it is found that the numerical simulation accuracy of seismic liquefaction shock in free-field sand ground can be improved to a certain degree by using reasonable permeability coefficient model.