Vertical vibration of a pile in a double-layered stratum under the freezing and thawing processes of saturated porous media

In permafrost or seasonally frozen regions, due to seasonal factors or engineering factors, an active layer is produced at the upper part of the stratum to form a double-layered foundation which has an effect on pile integrity test. The theories of Leclaire's frozen porous medium and Biot's porous medium are used to simulate permafrost and unfrozen soil, respectively. A simplified model for studying the vertical vibration of a pile embedded in double-layered soil is established. The double-layered stratum is divided into four types of cases, according to the freezing or thawing of the upper active layer in the permafrost or seasonally frozen regions, and the analytical solutions of the dynamic responses at the pile head are obtained. The result shows that the simplified double-layered model is in good agreement with the monolayer solution and can meet the needs of engineering research. The effect of stratification caused by freezing and thawing processes on the vertical vibration of a pile is studied via the parametric analysis method. The results show that the freezing and thawing processes of permafrost or seasonally frozen soil have an obvious influence on the reflected wave curves of the pile.