地震激励下冻土–液化土–单桩共同作用试验研究

地基土地震液化诱发的侧向扩展可导致桩基侧移过大甚至失效破坏,但如果场地存在冻土层,情况则变得复杂。通过试验研究了在地震作用下冻土、液化土和单桩三者之间的相互作用,分析了由于存在冻土层这一因素对地基液化和桩基承载性能的影响。试验中土体盛放在一个柔性模型箱当中,分为上下两层：下层为饱和砂土,上层为模拟冻土层。模拟的钢管桩嵌入土体之中,上部设有附加集中质量。测试过程中选取不同等级的调幅地震波对装置进行激励加载,分别观测桩身应变、桩与冻土层位移以及砂土内的孔隙水压力等参数。试验结果显示：地基土液化时,冻土层限制孔隙水排出而致使地基液化程度急剧发展,从而导致桩基的侧向变形快速增长；随着地震激励的增强,冻土层与桩体接触部位可能因挤压出现局部破损,导致二者分离；冻土层端面处桩体变形存在突变,此处桩体易于失效。

Experimental study on frozen soil-liquefiable soil-single pile interaction during earthquakes

Liquefaction-induced lateral gound spreading can result in excessive lateral displacement, even failure of piles, nevertheless the situation may be somewhat different in frozen ground. Shaking table tests are conducted with the purpose of investigating the corresponding influence. The soil profile, contained in a large flexible box, consists of a horizontally saturated sand layer overlaid with a simulated frozen soil layer. The simulated steel-pipe pile is embeded in these two soil layers, with a supplemental lumped mass at the top. The device is excited through several amplitude-scaled seismic waves with different levels. During the tests the strain of the pile, the displacements of the pile and the frozen-soil layer, and the pore water pressure in the sand are recorded. Some important conclusions can be drawn. When liquefaction occurs, the frozen-soil layer can suppress the pore water drains from the saturated sand soils and make the pore water pressure increase continuously. Hence, the liquefaction has the tendency to accelerate and the lateral displacement of the pile may increase significantly. With the increasing levels of seismic excitation, the position on the frozen crust corresponding to the contact surface of the frozen-soil layer and the pile may be damaged because of squeezing, and thus the contact surface cannot be maintained effectively any longer. The sudden changes in the lateral deformation of the pile occour at the positions corresponding to the bottom and the top surface of the frozen crust, and consequently these positions on the pile can be easily damaged.