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考虑土体液化和循环移动性的土体的动力响应。使用地震期间记录在土壤沉积物中的加速度和孔压来研究所提出的分析的有效性。分析结果包括加速度时程、孔压时程和傅立叶谱，与实测值吻合较好，验证了分析方法的有效性。该方法由修正的Penzien模型和水平地基反力模型组成，其中Penzien模型与有效应力分析相结合，水平地基反力模型将自由场反应与桩结构反应联系起来。对某大型集装箱中的土-桩-结构模型进行了振动台试验，并与理论分析结果进行了比较。分析结果包括超孔隙水压力时程、加速度时程、位移时程、地面和桩头的傅立叶谱，均与观测值吻合较好，说明该分析方法是有效的。对比分析结果表明：(1)无论桩的刚度如何，桩液化前的弯矩都受到土体变形的显著影响：(2)除非桩的刚性足够大，否则桩的变形对液化前的弯矩有很大的影响。桩的弯矩还受土体变形的影响：(3)桩的最大弯矩与地面变形的关系比与结构上测得的加速度关系更密切。在此基础上，提出了土体液化过程中桩的弯矩的简化估算方法。

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.