Study On The Anti Floating Characteristics Of The Concrete Bottom Sealing Structure Of Deep Foundation Pit

With the increasing of high-rise buildings in recent years,deep foundation pit has gradually become a hot issue in geotechnical engineering field.Deep foundation pits usually correspond to groundwater with high head,which makes anti-floating design crucial.In general anti-floating design,the methods of curtain for cutting off water,counterweight,uplift pile or anti-floating anchor are usually adopted.The concrete bottom sealing-partition wall(uplift wall)studied in this paper is a new type of anti-float structure,which is suitable for underwater excavation and plays the role of anti-float,support and convenient construction.Based on the foundation pit project of Yongdingmenwai station of Beijing metro line 8,this paper studies the mechanical properties of the new anti-floating structure by numerical simulation,and provides a theoretical reference for the optimization of the structure.The research of this paper is mainly divided into the following parts:1)A single wall model is built in PFC2 D software.By applying different uplift loads,the change of soil shear band in the process of wall uplift is explored,and the failure process of wall uplift under ultimate load is analyzed.Based on the model of bottom sealing and uplift wall,the uplift displacement of anti floating structure under different wall spacing is studied by changing the wall spacing.2)In midas /GTS software,the foundation pit model of Yongdingmenwai station was established,the foundation pit excavation was simulated by combining with the actual construction process,and the correctness of the model was verified by comparing the monitored value and simulated value of the underground diaphragm wall displacement.In the case of the same anti-floating safety factor,three anti-floating schemes of the partition wall method,the counterweight method and the uplift pile method were simulated,the displacement and bending moment of the bottom sealing in the three schemes are compared,and the stress and deformation rules of the partition wall method are summarized.And try to optimize the structure by changing the number of partition wall.3)Through numerical simulation,the lateral displacement of diaphragm wall with and without partition wall is compared,and then the supporting effect and influence range of partition wall on diaphragm wall are analyzed.The influence of the spacing,depth and elastic modulus of the partition wall on the lateral deformation of the diaphragm wall was investigated by using the control variable method.By means of the above methods,this new anti-floating structure is studied at the micro and macro levels,and some mechanical properties of the structure were obtained.The influence of the parameters such as the number of partition wall and material on the structure has been analyzed,which provides ideas for the optimization of the structure and can be used to guide the design of related projects in the future.