Evaluation of ultimate strength and deformation capacity of foundations during liquefaction and cyclic mobility

提出了一种有效的应力分析方法来模拟涉及土壤液化和循环迁移的土壤沉积物的动力响应。利用地震时在土壤沉积物中记录的加速度和孔隙压力来研究所提出的分析的有效性。加速度时程、孔隙压力时程和傅立叶谱分析结果与观测值吻合较好，表明了分析方法的有效性。提出了一种评价土-桩-结构体系液化过程动力响应的解析方法。该方法由结合有效应力分析的修正Penzien模型和将自由场响应与桩结构响应联系起来的水平路基反力模型组成。对大型容器内的土-桩-结构模型进行了振动台试验，并与分析结果进行了比较。分析结果表明，超孔隙水压力、超孔隙水加速度、超孔隙水位移时程以及地表和桩顶的傅立叶谱与观测值吻合较好，表明分析方法是有效的。试验与分析结果的对比表明：(1)无论桩身刚度如何，液化前桩身弯矩受土沉积变形的影响较大；(2)除非桩身足够刚性，否则桩身弯矩也会受到土沉积变形的影响；(3)桩身最大弯矩与地基变形的关系大于与结构上实测加速度的关系。在此基础上，提出了一种估算土体液化过程中桩身弯矩的简化方法。

An effective stress analysis procedure is proposed for simulating dynamic response of a soil deposit involving soil liquefaction and cyclic mobility. The effectiveness of the proposed analysis is studied using accelerations and pore pressures which were recorded in soil deposits during earthquakes. The analytical results including time histories of acceleration and pore pressure and Fourier spectra are in good agreement with the observed values, indicating the effectiveness of the proposed analysis.An analytical method is then presented for evaluating dynamic response of soil-pile-structure system during soil liquefaction. The method consists of a modified Penzien's model combined with the effective stress analysis and a horizontal subgrade reaction model which connects free field response with pilestructure response. Shaking table tests are conducted on soil-pile-structure models constructed in a large container, and the results are compared with analytical ones. The analytical results including the time histories of excess pore water pressures, accelerations, and displacements, and the Fourier spectra of the ground surface and the pile head, are all in good accord with the observed values, showing that the proposed analysis is effective.The comparison of experimental and analytical results indicate that : (1)regardless of the rigidity of pile, the bending moment of the pile before liquefaction is significantly influenced by the deformation of the soil deposit : (2)unless the pile is rigid enough, the bending moment of the pile is also influenced by the deformation of the soil deposit : (3)the maximum bending moment of the pile is related better to the ground deformation than to the acceleration measured on the structure. Based on the above findings, a simplified method is presented for estimating bending moment of piles during soil liquefaction.