To improve the disaster prevention and mitigation of metro shield tunnel

model test of similar material and numerical calculation is studied in this paper to simulate the construction of building adjacent to foundation pit in Beijing. Under unloading-loading conditions of the foundation pit above

the mechanical characteristics of shield tunnel are studied

and the influence of spacing between the bottom of the foundation pit and the shield tunnel top and the loading strength of foundation pit are also analyzed. As shown by calculation

in unloading stage

the vertical displacement of shield tunnel gradually increases. When the foundation pit is excavated to the bottom

the vertical displacement reaches the maximum value. Under loading condition

the vertical displacement of shield tunnel can be restored. The greatest impact on shield tunnel always occurs at the end of the foundation excavation. At this point

the work of foundation slab construction should be completed as soon as possible. In the unloading-loading process of foundation pit

earth pressure of shield tunnel presents calabash type symmetrical distribution. At the top and bottom of the shield tunnel the earth pressure is larger than the soil pressure in the middle of the shield tunnel. In unloading stage

the earth pressure of shield tunnel vertical axis was significantly reduced. In loading stage

the earth pressure of shield tunnel can be restored. With the spacing between the bottom of foundation pit and shield tunnel top increases

the displacement of shield tunnel

the displacement difference between arch bottom and arch and the horizontal convergence are incrementally reduced. When the spacing greater than 3 times of the depth of deep excavation

the additional deformation of shield tunnel caused by foundation pit unloading-loading effect is slightly. When the loading strength of foundation pit 2 times than the unloading strength

the vertical displacement of shield tunnel can be restored to its original state.