Abstract: The deformation of surrounding rock of tunnel in upper soil and lower sand strata constructed by threebench method is difficult to control. As a result, the surrounding rock deformation laws of Yangcheng Tunnel on HaolebaojiJi′an Railway under different burial depths and different ratios between upper soil and lower sand are analyzed by laboratory test, numerical simulation and theoretical analysis method; and the selection principles for surrounding rock deformation control method is put forward. The study results show that: (1) The deformation curves of surrounding rock of tunnel with different burial depths and different ratios between upper soil and lower sand can be divided into 4 stages, i.e. predevelopment, rapid development, slow development and stability; and the curves can be well fitted by Boltzmann function. (2) When the ratio between upper soil and lower sand increases from 0∶1 to 1∶0, the response laws of tunnel crown settlement, horizontal convergence and inverted arch uplift vary. (3) The selection principles for the surrounding rock deformation control methods of the tunnel in upper soil and lower sand strata constructed by threebench method are put forward, which are proved to be effective for surrounding rock deformation control.

Key words: tunnel engineering, upper soil and lower sand strata, surrounding rock deformation, control method, numerical simulation