Abstract:

In order to study the mechanical performance of buried isolation piles near subway shield tunnel,the deformation and earth pressure distribution of subway shield tunnel with buried isolation piles are studied and also the influences of three supporting systems, namely, buriedisolation pile, common isolation pile and no buriedisolation pile, on earth pressure and deformation of the existing tunnel are analyzed respectively, with the mixing method of model test and numerical simulation and based on a typical subway shield tunnel and its nearby foundation pit project in Beijing. The study results show that: (1) In the process of excavation and loading, as horizontal displacement of tunnel is far larger than the vertical displacement and uneven displacements existing in the horizontal and vertical directions of the tunnel, it can be concluded that the tunnel shows a trend of rotation towards the direction of foundation pit. (2)Horizontal displacement of tunnel decreases in buried isolation piles system, compared with no isolation piles system and the tunnel slightly rises, which indicates that the rotary trend of the tunnel has been effectively controlled. (3)The isolation effect of both buried isolation piles system and normal isolation piles system is basically the same. As for subway tunnel, the part of normal isolation pilesnear to the ground has nearly nothing to do with the control of tunnel deformation, in actual projects, applying the buried isolation piles can decrease the length of pile to lower the cost. (4)Initial earth pressure of tunnel is distributed as gourd shape. In the process of excavation and loading, the distribution of earth pressure deflects. It can be concluded that the tunnel shows a trend of rotation towards the direction of foundation pit. The buried isolation piles effectively decrease earth pressure of tunnel, and the effect is as the same as that of the normal isolation piles.

Key words: subway, shield tunnel, buried isolation pile, soil unloading, the foundation loading, similar material model test, numerical simulation