(1. Department of Civil Engineering，Zhejiang University City College，Hangzhou，Zhejiang 310015，China；
2. College of Civil Engineering and Architecture，Zhejiang University，Hangzhou，Zhejiang 310058，China)
Abstract：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 into the 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.
2016, Vol. 35 
