Study On Pile Foundation Underpinning Techniques In Subway Construction

With the development of the cities'construction, the ground traffic becomes too much heavy. Many cities choose to build Subway which is convenient and efficient to alleviate the traffic pressure on the ground. Undercutting method becomes the main way to build subway in most cities, because of its little influence to the ground traffic and its widely application. Some tunnels are inevitable to go through the foundations of the construction on the ground, and the foundations which enter into the tunnel must be underpinned. Many buildings are supported by pile foundations. Therefore, it is of great importance to study the displacement of the old foundation and the mechanic behavior of the tunnel's lining in pile foundation underpinning.Firstly, the author summarized the type and the characteristic of the foundation underpinning methods which partly go through the construction in open-cut subway and go through the construction in total in undercutting subway, and the FEM theory is introduced simply in this dissertation.Next, based on the Tiantan East-station of Beijing No.5 Subway which goes through the pile foundation of the 109th high school's passenger footbridge, the underpinning scheme that the newly built pile and the old pile supporting the upper load is constituted, and in the scheme truncating the pile in the tunnel is also determined. Then the construction process is imitated with FEM software. At last, it is proved that this underpinning scheme is rational and feasible by the comparison of the imitation result and the actual measured result.And then, based on the left tunnel of PuTian of Beijing subway which goes through the pile foundation of the South Moat, in the case of lacking the condition to actualize pile foundation underpinning on the ground, the underpinning scheme in the tunnel is constituted firstly. This scheme is actualized by adding the tunnel's supports and several new techniques such as the followings: inserting reinforced bars, shelling piles, lining arch, truncating piles and secondary lining arch. Then the tunnel support and lining arches become the new foundation of the old pile. In the following study,...