Analysis Of The Floating Effect Of Groundwater On Underground Structures Under Rainfall Conditions

In recent years,with the rapid development of China’s construction industry,there are more and more underground construction projects in most cities.In some places with abundant groundwater resources,due to ignoring the buoyancy of groundwater,the underground structure fails to resist floating,and accidents of underground structure tilting or cracking of components often occur.The fundamental reason is that the setting of antifloating fortification water level is low or the rise of groundwater level caused by heavy rainfall in rainy season is not considered.Therefore,in order to reasonably determine the anti-floating fortification water level of underground structures,explore the influencing factors and laws of underground water level changes,and analyze the causes of underground structures’ floating damage,this paper has carried out a series of research and analysis based on an actual project in Qinhuangdao.Firstly,this paper analyzes and summarizes the research status of determining the antifloating fortification water level of underground structures and the calculation methods of groundwater buoyancy at home and abroad.This paper further analyzes the research status of anti-floating measures of underground structures at home and abroad,and briefly introduces three failure modes of anti-floating failure of underground structures and the antifloating measures that can be adopted.Combined with the case of floating damage of an underground garage in Qinhuangdao,it is analyzed that the root cause of the accident is that the anti-floating fortification water level of underground structure is low,and the adverse impact of heavy rainfall in rainy season on underground structure is ignored.The Midas GTS finite element software is used to establish a three-dimensional calculation model,and the change of groundwater level and the deformation of the garage raft under different working conditions are analyzed.The analysis conditions are stable water level,continuous rainfall A1,continuous rainfall A2 and heavy rainfall B1.The deformation of underground structure foundation under different conditions is simulated and analyzed.The distribution of pore water pressure at the bottom of raft under continuous rainfall conditions A1,A2 and heavy rainfall conditions B1 is compared and analyzed.Under the same rainfall conditions,the influence of different permeability coefficients of backfill on the pore water pressure at the bottom of raft and the floating of raft are also analyzed.The results show that the pore water pressure in the edge area of raft is larger than that in the middle area.The permeability coefficient of backfill soil has great influence on the distribution of pore water pressure at raft position.Through the maximum pore water pressure to reverse the change of groundwater level,the rise of groundwater level around underground structures is positively correlated with rainfall intensity,rainfall time and the permeability coefficient of backfill around underground structures.Under the same rainfall conditions,with the duration of rainfall time,the floating of raft of underground structures becomes more and more serious.