中文摘要：

近年人工冻结法在地铁联络通道施工中得到广泛应用,土体经过冻融后工程性质将发生改变。通过室内不排水动三轴试验模拟冻结法施工后冻融土在地铁列车荷载作用下的动力特性,针对重塑黏土开展冻结温度和冻融周期影响下的动孔压测试试验,并首次提出了考虑冻结温度和冻融周期的孔压发展模型。结合扫描电子显微镜（SEM）试验,对软土冻融后及循环加载后微观结构的变化进行分析,从微观角度揭示冻融软土宏观特性的变化机制。试验结果表明：冻结温度越低,在循环荷载作用下孔压发展速率越快,稳定孔压也越大;随着冻融循环次数的增加,软土结构弱化效应越明显,将会加剧孔压发展;对比软土冻融前后的微观结构可以看出,冻融循环过程将破坏土颗粒之间的联结作用,导致颗粒骨架重新排布,微小孔隙联结成为较大孔隙,结构性发生弱化效应,处于非稳定状态;在循环加载过程中,外部传递的能量使内部结构向稳定状态发展,大孔隙体积逐渐减少,发生较为显著的挤密作用,微观结构的变化在宏观表现为超孔压的累积和变形的发展。并基于试验数据,采用复合指数函数对孔压发展曲线进行非线性多元拟合,建立循环孔压累积经验模型,结果表明,拟合效果较好。

英文摘要：

In recent years,artificial freezing method has widely been used in the construction of connection tunnel between metro tunnels. The engineering properties of soil change under the freezing-thawing action. In this paper,the dynamic characteristics of frozen-thawed soil were studied with the undrained dynamic triaxial test in laboratory to simulate the effect of artificial freezing. Dynamic pore pressure of remolded clay was measured during the cycles of freezing and thawing. A new pore pressure model was proposed. The microstructure change of soil during the cycles of freezing and thawing was analyzed with the scanning electron microscope（SEM）. The macroscopic characteristics of deformation were revealed from the microscopic perspective. The lower the freezing temperature,the faster the development of pore pressure and the larger the stable value under cyclic loading. With the increase of freezing-thawing cycles,the weakening effect of soil structure increases. The freezing-thawing action breaks the link between the soil particles,resulting in the re-arrangement of grain skeleton and the development of large micro-pore. Then,structural weakening effect occurrs which leads the structure intothe instable state. Due to the external energy,the internal structure tends to be steady during cyclic loading. The decrease of the volume of macro pore further leads to a more significant compaction of frozen-thawed soil,which causes the accumulation of excess pore pressure and the development of deformation in macro perspective. Multivariable nonlinear fitting of pore pressure described by the composite exponential model based on the experimental data was proposed and the proposed pore pressure model fit the data well.