Comparative Analysis Of Mechanical Characteristics Of Construction Of Transverse Tunnel Cover Method And PBA Construction Method In Subway Station

In order to reduce the interference of urban traffic during the construction process,the subway station usually adopts the shallow buried method,and the PBA method is the most widely used.However,there are many shortcomings in the PBA method.One is that the small number of holes and the formation of a complete lateral force structure in the top of the station,the number of times of force conversion is complicated and the construction is complicated;the second is that the advanced support is long in the longitudinal direction,construction The working surface is small,the construction precision is high,and the construction period is long.The third is that the station forms a V-shaped node at the top of the column,which makes the structure difficult to prevent and drain.In order to solve the above problems,China's civil engineers proposed a new method of underground excavation of subway stations-the horizontal hole cover method.The main advantage of this method is that a temporary lateral bearing system with a large rigidity can be formed once in the longitudinal guide hole,which reduces the number of force conversion,and the construction node is simple and the transmission force is clear.Based on a metro station in Shijiazhuang,this study used the Midas GTS finite element software to simulate the PBA method and the transverse hole cover method respectively.The stratum displacement,surface settlement and structure affected by the two methods were analyzed.The law of force and plastic zone changes.Then,the construction sequence of the two methods and the structural parameters of the new method are optimized.Finally,the applicability of the two methods to different depths is studied.The research results have important guiding significance for on-site construction,and also provide theoretical support for the promotion and application of new construction methods.The research contents and conclusions of this paper are as follows:(1)The two methods are similar in the process of stratum displacement,plastic zone change and structural stress during the construction phase.Under the current engineering background,the PBA method is more conducive to controlling surface settlement,while the lateral cavity cover method is less stressed.(2)Under the current geological conditions,regardless of the lateral hole cover method or the PBA method,the small guide hole adopts the excavation sequence of"first up,down,first and then back",and the excavation of the station floor and platform is "first" The surface settlement caused by the excavation sequence of the span and the mid-span is minimal;the excavation sequence of the tunnel has a greater impact on the surface settlement caused by the lateral tunneling method,and the excavation sequence of the station has little effect on the surface settlement.(3)The guiding hole in the upper layer of the lateral hole cover method is used as the leading guiding hole,which is not only convenient for construction,but also more favorable for controlling the ground settlement and reducing the structural stress.(4)The jacking stiffness and jacking range of the transverse hole cover method have little effect on the surface settlement.The D400 pipe jacking is adopted,and the jacking pipe is pushed into the outside of the station 2m,which is most beneficial for controlling surface subsidence.(5)Under the same geological conditions,the surface settlement of the two methods in the range of 4?9m buried depth increases with the increase of the buried depth,the buried depth is less than 6.5m,and the surface settlement caused by the transverse hole cover method Smaller,buried depth is more than 6.5m,PBA method is better for surface settlement control,and horizontal hole cover method is more suitable for ultra-shallow burial.