The Engineering Characteristics of Uplift Piles in Soft Clay

As densely populated urban areas increasingly focus on the development of underground space, engineers are concerned with solving the problem of antifloating design for underground structures. This study focuses on two landmark projects in the Wenzhou area. Through in-depth comparison and analysis of long-term on-site data, the aim is to reveal the mechanism of pore water pressure formation in antifloating pile foundation engineering and the mechanical response of pile foundation structures under different working conditions. To analyze the variation in pore water pressure over time, spanning from deep excavation to postcast zone sealing, and to ascertain the disparity between theoretical and actual buoyancy values, long-term monitoring was conducted on selected piles at distinct test sites within soft clay. The internal forces within the specified section of the pile were monitored. Sensors were embedded in specific locations to capture variations in groundwater levels and pile body stress, and data were collected in real-time. The test spanned over 400 days, during which the impact of changing test site conditions and environmental factors on pile performance was analyzed. The observation results show that: (1) After the closure of the basement structure floor and the removal of drainage measures, groundwater movement becomes the main cause of the rise in pore water pressure, followed by rainfall. (2) The theoretical buoyancy and actual buoyancy rate in the deep soft clay layer have decreased, and the decrease in pore water pressure has a direct impact on buoyancy, which is influenced by two key factors: permeability coefficient and soil layer thickness. (3) The increase in pore water pressure in a short period of time will lead to a rapid decrease in buoyancy rate.