The buoyancy of groundwater in clay layers is a critical factor that influences the behavior of geotechnical engineering structures. However, there is still a lack of understanding regarding the factors that contribute to the reduction of groundwater buoyancy. This study aims to elucidate the influence of soil parameters and matric suction on groundwater buoyancy, employing laboratory model tests and innovative experimental methods. The research findings uncover noteworthy variations in the reduction coefficient of groundwater buoyancy contingent upon the clay type, ranging from 0.45 to 0.85. Furthermore, experimental results indicate that matrix suction effectively diminishes pore water pressure but exerts minimal influence on groundwater buoyancy. It is elucidated that pore ratio, permeability coefficient, and water content evince a robust positive correlation with the buoyancy reduction coefficient, whereas dry density and wet density exhibit an inverse trend. Conversely, parameters such as cohesion, saturation, internal friction angle, specific gravity, liquid limit, and plastic limit manifest minimal correlation with the buoyancy reduction coefficient. These findings have practical implications for anti -floating design in geotechnical engineering.

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.