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

通过振动台试验，研究了土-桩-结构动力相互作用的液化过程。在长4 m、宽2 m、深2 m的大型集装箱内建立了砂堆-桩-结构模型体系。由堆叠的钢板组成的容器可以允许土壤的剪切变形。然后进行振动台液化试验，其中土壤密度，桩直径，桩刚度，液化层厚度和输入运动的控制变量。试验过程中对土-桩-结构体系的孔隙水压力、加速度、变形以及桩身弯矩进行了监测和记录，结合振动台试验结果和基本情况进行了分析，结果表明：（1）无论桩的刚度如何，液化前土-结构体系的动力响应受土存款的影响显著，（2）除非桩有足够的刚度，否则土-结构体系在液化后的动力响应也会受到土的响应的影响;（3）桩的最大弯矩与地表的最大变形的关系比与结构和地表上测得的最大加速度的关系更好。提出了考虑液化引起的桩水平地基反力系数的递变和土模量递变的分析方法。对液化和非液化两种情况进行了分析，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反应谱，均与实测值符合雅阁，表明所采用的模型是合理的。

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.