For the shallow tunnel of Qizishan with small net distance bias,the typical locations of the tunnel were selected to establish a fine three-dimensional model,and the tunnel construction process un-der different construction sequences was simulated.The effects of three different construction sequences of bias side first,bias side second and simultaneous construction on the formation deformation and struc-tural stress were studied,which provided a basis for the determination of construction sequence.The re-sults show that the first construction on the bias side causes the largest stratum displacement,followed by the simultaneous construction,and the last is the backward construction on the bias side.The maxi-mum variation of the vertical and horizontal displacement of the stratum caused by the construction se-quence is 15.50%and 62.50%respectively,and the maximum variation of the internal force of the supporting structure is 22.63%.Considering that the formation displacement and structural force varia-tion caused by the change of construction sequence are within the allowable range,the on-site construc-tion of Qizishan tunnel adopts the scheme of simultaneous tunneling of left and right lines,and the cons-truction process and monitoring data verify its rationality.
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