Consolidation Analysis of Saturated Clay around a Permeable Pipe Pile Based on Fractional Derivative-Based Model

Permeable pipe pile integrates drainage and bearing functions, and it promotes the bearing capacity of the pile foundation by accelerating the consolidation of the soil around the pile. To investigate the consolidation characteristics of the saturated clay around a permeable pipe pile, the axisymmetric consolidation model of saturated clay around a permeable pipe pile is established by adopting the fractional derivative-based Merchant model to describe the rheological behavior of the clay, and at the same time using the impeded drainage boundary to simulate the drainage condition of the pile-soil interface. By means of the separation of variables method and Laplace transformation, the corresponding consolidation solution is obtained, and then its reasonableness is verified by comparing with the experimental results and the existing solutions. Based on the obtained solutions, the parametric analyses are carried out to investigate the influence of relevant parameters of the soil and the permeable pipe pile on the consolidation behaviors of the clay around the pile. The results indicate that the fractional order has a considerable effect on the creep stage of the clay, while it has little impact on the dissipation process of excess pore water pressure. The dissipation of excess pore water pressure is not synchronous with the settlement development in the soil around the pile, but the gap between them decreases with the increase in the fractional order. The increase in both viscosity coefficient and pile-soil interface parameter accelerates the dissipation of excess pore water pressure, and the former slows down the creep rate of the soil, while the latter does not affect the creep development of the soil.