Application Study On Anti-floating Reliability Of Random Water Level Distribution Analysis During Construction Of Super-large Underground Structure

With the development of urban underground space development in China,the underground structure anti-floating failure accidents are common.Many studies have shown that happen during construction period is anti-floating failure hour.The lack of existing research for anti-floating of attention during the construction,structure of anti-floating capacity is limited to the use of safe coefficient to evaluate,and ignored the many factors that influence the anti-floating.Therefore,in order to put forward an effective anti-floating research method,this paper conducted the following research:(1)The objective of the paper is to establish the finite element model for anti-floating reliability analysis.The paper based on ANSYS finite element software,to build a model of an underground garage of a project that had anti-floating failure in Kaifu District,Changsha.Then we loaded the measured water level of the project site into the model in the form of load steps to obtain the bottom plate deformation data at the same time as the two actual measurements in the model and compare them with the actual measured values to verify the rationality of the model.The results showed that the fitting effect is good and the model can be used in subsequent studies.(2)Reliability analysis of anti-floating: step loading was used to study the mechanical characteristics of the structure under the action of water buoyancy and determine the discriminant basis of anti-floating failure.The finite element model in the second chapter was analyzed according to the three stages of construction and the validity period.The sensitivity analysis of several factors affecting anti-floating was carried out.Considering the secondary damage caused by the continuous influence of water level on the structure,the analysis was made based on several damage states.The results showed that with the tensile failure of the floating pile,the superstructure was destroyed one after another,so the tensile failure of the floating pile was taken as the judging basis of the anti-floating failure.The anti-floating ability of the structure reflected by the reliability analysis results was consistent with the actual situation.The sensitivity analysis showed that the water level is the most important factor.The analysis results of the damage state showed that,with the increase of the damage proportion,the reliability index of the structure decreases and the failure probability increases.The variation range is related to the damage proportion.When the damage proportion is less than 14%,the variation range will be relatively gentle,and the variation range will be very large from 14% to 16%,and then will tend to be gentle.(3)Study the influence of clay and sand on the anti-floating reliability by using the anti-floating model test:Three kinds of counterweights and three groups of water level distribution were designed.The model boxes with three kinds of counterweights were placed in pure water,clay and sand soil respectively to get the reliability under different working conditions.The reliability index of the same counterweights and water level was compared.The results showed that the reliability in sand soil was 1.2 times that in pure water.However,the reliability index in clay is1.73 times higher than that in pure water in the other two working conditions,which provides a basis for the optimization of anti-floating reliability index.(4)In chapter 3,the feasibility of reliability analysis is verified and the water level distribution is the most important factor.On this basis,the anti-floating early warning mechanism based on the prediction of water level in construction period is put forward.