砂土非极限位移状态动土压力形成机理及拟动力计算研究

The retaining structure is generally subjected to dynamic earth pressure due to earthquake or traffic loads. However, since the lateral deformation of the structure is under strict control or the displacement modes are different, the structure can not reach the limit displacement state required in the conventional earth pressure theory and thus it works in the non-limit displacement state. The existing methods can not accurately describe this kind problem of dynamic earth pressure. In this project the saturated sand is regarded as the main research object. Firstly, it is proposed to study the development of asymptotic state for the sand under cycle dynamic loads by the dynamic triaxial tests with controlled strain increment ratio. Then the quantitative relationship between stress ratio and strain increment ratio when the sand reaches asymptotic state is revealed. Secondly, the influences of the waveform, vibration times and frequency of the cycle dynamic loads on the asymptotic state for sand are analyzed, and a comparative study of the effect of the sand density and the consolidation state on the asymptotic state is carried out in order to explain the mechanics nature and the formation mechanism of dynamic earth pressure. Finally, the corresponding relationship between the mobilized friction angle of soil and the strain increment ratio under dynamic loads is summarized based on the experiments, and the pseudo-dynamic method is derived which can be applied to the dynamic earth pressure under non-limit displacement state. The interaction among the structure displacement, dynamic loads and earth pressure is established consequently. The calculation diagrams for engineering design are given, which will provide a theoretical reference for improving the method of the dynamic earth pressure in retaining and underground structure.

挡土结构普遍承受着地震或交通荷载引起的动土压力。但是，由于结构受到严格的侧向变形控制或存在位移模式的差异，无法达到传统土压力理论所需的极限位移状态，而是处于非极限位移状态下工作。现有计算方法无法准确地描述这类动土压力问题。本项目主要以饱和砂土为研究对象，通过控制应变增量比的动三轴试验，研究周期动荷载作用下砂土渐近状态的发展过程，揭示砂土达到渐近状态时的应力比与应变增量比的定量关系。分析周期动荷载的波形、振次和频率对砂土渐近状态的作用规律，对比砂土密实度和固结状态对砂土渐近状态的影响，从而阐释动土压力的力学本质和形成机理。在试验的基础上，总结动荷载下填土起动摩擦角与应变增量比的对应关系，推导提出可适用于非极限位移状态的动土压力拟动力计算方法，从而建立结构位移-动荷载作用-土压力这三者之间的作用关系。给出工程设计的计算图表，为改进支挡结构和地下结构的动土压力计算方法提供理论参考。

挡土结构普遍承受着地震或交通荷载引起的动土压力。但是，由于结构受到严格的侧向变形控制或存在位移模式的差异，通常是处于非极限位移状态下工作，现有计算方法无法准确地描述这类动土压力问题。本项目以地震荷载下的刚性挡土墙为研究对象，基于试验得出的结构-位移函数，总结了填土内摩擦角和墙土外摩擦角的发挥值与挡墙位移量的对应关系，结合水平层分析法和极限平衡理论，建立了可适用于非极限位移状态的动土压力拟动力计算方法，阐释了土体强度随结构位移状态的发展过程。推导建立挡土墙RB、RT、T模式下的地震非极限土压力和合力作用点的计算表达式。计算模型根据墙顶、墙底最大位移的不同分成2种非极限状态工况，可描述摩擦角沿着墙高逐渐发展的不同非极限位移状态工况，并建立了挡墙位移，地震动荷载和土压力之间的相互联系，揭示了非极限动土压力的形成机理。同时，考虑浸水条件下的挡土墙，建立了可计算地震主动和被动土压力的改进拟动力法，分析了浸水工况、二维渗流工况以及各项异性的渗流系数对地震土压力的影响，此外，针对临水的加筋挡土墙，提出了考虑地震作用和浸水条件综合影响的加筋条拉力计算方法。结果表明，RB模式下，土压力随挡墙位移增大而逐渐减小，直到达到主动极限状态；而挡墙的位移量越大，合力作用点高度却越低。对于RT位移模式，地震作用的影响则主要位于土压力曲线的中上部。挡墙位移量对合力的影响相对较小；挡墙位移量越大，土压力合力作用点越高。研究成果对改善支挡结构的抗震设计具有一定的理论参考意义。

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