As underground structures' burial depth increases, buoyancy resistance due to groundwater becomes more pronounced. This study, through numerical simulation, analysis of field measurement data, and theoretical analysis, explores the impact of changes in groundwater level on the failure mode and uplift resistance of expanded base piles and proposes a new method for calculating the ultimate uplift capacity of expanded base piles considering the effect of groundwater. The research shows that the rise in groundwater level significantly affects the uplift performance of expanded base piles by altering the physical and mechanical properties of the soil and the morphology of the pile-soil failure surface, thereby affecting the pile's load-bearing capacity. The study identifies a three-segment failure mode for expanded base piles and notes that as the groundwater level rises, the extent of the failure surface gradually expands. Additionally, the paper underscores the importance of considering groundwater levels in practical engineering design and suggests re-evaluating the measured uplift capacity using the calculation method proposed in this study to ensure engineering safety. This research provides a theoretical basis and computational tools for designing belled uplift piles under the influence of groundwater, offering significant reference value for engineering practice.

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.

Gas hydrates formed in oceans and permafrost occur in vast quantities on Earth representing both a massive potential fuel source and a large threat in climate forecasts. They have been predicted to be important on other bodies in our solar systems such as Enceladus, a moon of Saturn. CO2-hydrates likely drive the massive gas-rich water plumes seen and sampled by the spacecraft Cassini, and the source of these hydrates is thought to be due to buoyant gas hydrate particles. Dispersion forces can in some cases cause gas hydrates at thermal equilibrium to be coated in a 3-4 nm thick film of ice, or to contact water directly, depending on which gas they contain. As an example, the results are valid at a quadruple point of the water-CO2 gas hydrate system, where a film is formed not only for the model with pure ice but also in the presence of impurities in water or in the ice layer. These films are shown to significantly alter the properties of the gas hydrate clusters, for example, whether they float or sink. It is also expected to influence gas hydrate growth and gas leakage.

This review presents a synthesis of four decades of palsa studies based on field experiments and observations mainly in Fennoscandia, as well as laboratory measurements. Palsas are peat-covered mounds with a permanently frozen core: in Finnish Lapland, they range from 0.5 to 7 m in height and from 2 to 150 m in diameter. These small landforms are characteristic of the southern margin of the discontinuous permafrost zone. Palsa formation requires certain environmental conditions: long-lasting air temperature below 0 degrees C, thin snow cover, and low summer precipitation. The development and persistence of their frozen core is sensitive to the physical properties of peat. The thermal conductivity of wet and frozen peat is high, and it decreases significantly as the peat dries and thaws. This affects the development of the active layer and makes its response to climate change complex. The insulating properties of dry peat during hot and dry summers moderate the thawing of the active layer on palsas. In contrast, humid and wet weather during the summer causes deep thawing and may destroy the frozen core of palsas. Ice layers in palsas have previously been interpreted as ice segregation features but because peat is not frost-susceptible, the ice layers are now reinterpreted as resulting from ice growth at the base of a frozen core that is effectively floating in a mire. (C) 2010 University of Washington. Published by Elsevier Inc. All rights reserved.