Effects of soil liquefaction on horizontal subgrade reaction of pile during earthquakes

采用振动台试验研究了土体液化过程中桩-土动力相互作用。在长4m、宽2m、深2m的大型集装箱中，构建了砂堆-桩-结构体系模型。该容器由堆叠的钢板组成，可允许土体剪切变形。以土密度、桩径、桩刚度、液化层厚度和输入运动为控制变量，进行振动台液化试验。监测并记录了试验过程中土-桩-结构体系的孔隙压力、加速度、变形和桩的弯矩。通过对振动台试验结果的分析，结合基本资料表明：(1)在不考虑桩刚度的情况下，液化前土-结构体系的动力响应受到土沉积物响应的显著影响；(2)除非桩刚度足够大，液化后土-结构体系的动力响应也会受到土响应的影响；(3)桩的最大弯矩与地表最大变形的关系大于与结构和地表最大加速度的关系。为了模拟上述结果，本文提出了考虑液化作用下桩基水平反力系数退化和土模量退化的分析方法。对液化和非液化情况进行了分析，并与实测值进行了比较。分析结果包括桩的加速度、位移、弯矩时程，以及地表和结构的响应谱，与观测值吻合较好，说明分析模型是合理的。

Shaking table tests were conducted to study dynamic soil-pile- structure interaction during soil liquefaction. A model sand deposit-pile-structure system was constructed in a large container 4m long, 2m wide and 2 m deep. The container, consisting of stacked steel plates, can allow shear deformation of the soil. Shaking table liquefaction tests were then conducted in which soil density, pile diameter, pile rigidity, thickness of the liquefied layer and input motion were controlling variables. Pore pressure, acceleration, and deformation of soil-pile-structure system, and bending moment of pile were monitored and recorded during the test.The analysis of shaking table test results together with the basic information indicated that: (1) regardless of the rigidity of pile, the dynamic response of the soil-structure system before liquefaction is significantly influenced by the response of soil deposit, (2) unless the pile is rigid enough, the dynamic response of the soil-structure system after liquefaction is also influenced by the response of soil, and (3) the maximum bending moment of the pile is related better to the maximum deformation of the ground surface than to maximum accelerations measured on the structure and the ground surface.In order to simulate the above findings, analytical method was developed in which regradation of the coefficient of horizontal subgrade reaction of pile due to liquefaction is taken into account as well as the regradation of soil modulus. Analysis was made for both liquefied and non-liquefied cases, and the results were compared with the measured values. The analytical results including the time histories of acceleration, displacement, and bending moment of pile, and the response spectra of the ground surface and structure, are all in good accord with the observed values, showing that the model used in the analysis is reasonable.