A mathematical model is proposed to investigate the dynamic behavior of an end-bearing pile under vertical seismic loading in a water-pile-saturated soil system. The model is based on the Euler-Bernoulli beam theory and takes into account the stress balance between pile sections, representing the pile as a one-dimensional rod. The overall response of site is divided into two components: the free-field response and the scattered-field response. The pile and soil are considered as linearly viscoelastic materials with hysteresis-based damping, while water is modeled as a linear acoustic medium. By accounting for boundary conditions involving force equilibrium and displacement continuity at the pile-soil and water-soil interfaces, an analytical solution for the system response is derived. Analytical expressions of pore water pressure and displacements are obtained, on the basis of considering water-soil interaction in both fields. A parameterization study is then conducted to evaluate the impact of key parameters on the vibration characteristics of piles in a water-pile-saturated soil system.

CPTu (piezocone penetration test) is widely used in engineering practice to determine various parameters of clays under partially drained conditions. However, most existing research is based on undrained or fully drained conditions for clays, leading to underestimation or overestimation of soil strength. By applying the Eulerian-Lagrangian large deformation finite element method to analyse the water-soil interaction, the CPTu driving mechanism in offshore saturated soft clays under different drainage conditions is revealed. An advanced hypoplastic constitutive model for clays is used to simulate the nonlinear behaviour of kaolin under different drainage conditions. The generation, accumulation, and dissipation of excess pore water pressure under different drainage conditions are analysed, as well as the influence of excess pore water pressure on cone tip resistance and the effective stress of the soil during the CPTu penetration process.

Based on the effective stress principle, indoor model tests were conducted in this study to calculate the buoyancy of an underground structure and determine the law of pore water pressure conduction in silty clay strata. A comprehensive underground structure-water-soil interaction test system was established with four-in-one features: Elimination of lateral friction, controllable water head, circulating water supply and drainage, and simulation of groundwater flow. Fourand seven-gradient buoyancy continuous monitoring tests were completed using fine sand and silty clay, respectively, to verify the reliability and accuracy of the test system. The hydrostatic pressure and seepage-hydrostatic process of the silty clay strata were simulated separately to investigate the buoyancy of the underground structure of the strata, the buoyancy reduction coefficient, and the pore water pressure conduction law. The results show the reliability and accuracy of the comprehensive test system for underground structure-water-soil interaction. The concept of buoyancy starting intercept is proposed based on this system, where the underground water level value should be the head of water supply minus the buoyancy starting intercept when calculating buoyancy in weak permeable layers. Under hydrostatic action, the groundwater is phreatic, deeper burial depths show greater magnitude of this discount. When the groundwater is confined, the water head reduction coefficient increases with increase in the burial depth or hydraulic gradient. Buoyancy calculations of an underground structure within the range of confined water should not be reduced in this case. Whether in a seepage or hydrostatic state, the pore water pressure in the silty clay layer is below the theoretical value. The results of this work may provide a theoretical basis for further analysis of the pore water pressure conduction law and buoyancy reduction mechanism of clay soils. We also may provide a theoretical reference for the development of innovative underground structure-water-soil interaction comprehensive test systems.