Fertilizer Tank Effect And Fertilizer Tank Water Level Control For Floatation Resistance Failure Of Underground Buildings In Weakly Permeable Sites

In recent years,the underground structure of the weakly permeable site anti-floating failure accidents occur frequently.In Chengdu,three similar accidents occurred in succession,all of which were caused by surface water infiltrating into the fertilizer tank after rainfall,and the impermeable layer of the pit and foundation easily formed the "water basin effect",resulting in the rise of groundwater pressure,which led to a series of anti-floating accidents.The rising height of the water level in the fertilizer tank is an important parameter to determine the size of the impact of a single rainfall,and it is also the main parameter to judge whether the antifloating accident occurs or not.Therefore,through the method of field test and numerical simulation,the thesis researched the influence law of rainfall time,rainfall intensity,infiltration coefficient,fertilizer tank slope,fertilizer tank width and other factors on the change of fertilizer tank water level in the foundation pit,established the empirical formula for calculating the change of fertilizer tank water level and proposed the targeted fertilizer tank water level control method.The main results of this thesis are as follows:(1)Through field test analysis,the mechanism of anti-floating failure occurred in such sites is clarified.The relationship between the recharge and discharge of the site water source was obtained.After the rainfall occurs,the rainwater continuously recharges to the fertilizer tank and the miscellaneous fill,the permeability coefficient of the fertilizer tank is higher than that of the miscellaneous fill,the water level falls quickly,and the upper layer of stagnant water in the miscellaneous fill continues to recharge to the fertilizer tank.After the rainfall,the water level of fertilizer tank and miscellaneous fill rose significantly,and after the rainfall ended,the water level of fertilizer tank gradually decreased,and about 3 days after the rainfall,the water level of fertilizer tank stabilized and the influence cycle of single rainfall ended.(2)Numerical simulation analysis using Midas Gts Nx was conducted to study the influence law of different influencing parameters on fertilizer tank water level(rainfall duration,rainfall intensity,infiltration coefficient,fertilizer tank slope and fertilizer tank width),and the influence law of related parameters on fertilizer tank water level was derived,among which rainfall duration and rainfall intensity were important influencing parameters,and the width of fertilizer tank bottom had less influence on fertilizer tank water level,and the water level of single rainfall The variation of water level in a single rainfall is about 0.2m.(3)Establishing the qualitative theoretical formula of fertilizer tank water level,and comparing the calculation results with the numerical simulation results,the results show that the accuracy of the theoretical formula is low,and the theoretical formula needs to be corrected,and the corrected calculation results should be greater than the numerical simulation of the fertilizer tank water level results to ensure the accuracy of the floatation resistance of the building structure.(4)Using engineering cases to verify the derived theoretical formula,according to the actual engineering situation and engineering survey data,the water level of the fat tank in extreme cases is calculated to rise by 2.97 m,then the value of the anti-floating water level is 419 m,the actual engineering experience,the anti-floating water level is 421.3m,the value of the qualitative formula is smaller than the value of engineering experience,which is more The value of the qualitative calculation formula is smaller than the value of engineering experience,which is closer to the actual value and can save the relevant design cost.(5)The reinforcement plan for existing projects in such sites was designed,adopting the basic idea of "interception" and "drainage",adding automatic drainage and pressure relief measures on the basis of not destroying the function of the basement structure of the original building,and monitoring the drainage measures for a long time.Monitoring results show that the drainage measures have good anti-floating effect.