Research On Buoyancy In Anti-floating Design Of Underground Structures

With the high-speed increase of the national economy, the accelerating process of urbanization, urban land resources has become increasingly scarce, which triggered a wave of development and utilization of urban underground space. However, the complex dynamic changes of groundwater is restricting the safe and reliable operation of underground structures strongly. The presence of groundwater has led to a series of engineering problems, of which the groundwater buoyancy effect on underground structure basement is the most prominent. The value of anti-floating water level and the buoyancy of underground structures are reasonable or not determine not only the safety of the entire structure, and have a great impact on the engineering design, cost and duration.Based on the above research background, this paper systematically studies the value of anti-floating water level, the buoyancy and its reduction of underground structures. Provide a reference for anti-floating design of actual engineering. The main work and results in this thesis as follows:1.The anti-floating water level of the underground structure should be the highest water level throughout the whole operation period of the groundwater aquifer which plays a leading role in the buried deep within the scope of underground structure foundation.2.Baced on the unique microstructure features of cohesive soil, this paper expounds the migration mechanism of bound water in cohesive soil, analyzes the mechanism of groundwater buoyancy and the applicability of the principle of effective stress in the cohesive soil.3.Introducing the current internal advanced indoor model tests for the study of groundwater buoyancy effect mechanism. Furthermore, using MIDAS/GTS numerical analysis software, underground structures under different soil layer combination and different types of groundwater conditions were stimulated. Through the numerical simulation, obtained that when the foundation slab of the underground structure is located in sand soil layer, the buoyancy of the underground structure should be calculated according to the hydrostatic pressure, when the foundation slab of the underground structure is located in the clayey silt or silty clay layer, the buoyancy of the underground structure should be multiplied by a reasonable reduction coefficient based on the hydrostatic pressure.4.Using MIDAS/GTS numerical analysis software stimulated a typical two-layer basement in Changsha. Compared with the groundwater buoyancy value calculated by traditional method, the buoyancy value which calculated by MIDAS/GTS software was much smaller. This shows that using traditional method to calculate the buoyancy of underground structure has certain limitations.