Abstract: There are a series of technical problems in TBM positioning and stepping device installing in TBM secondary stepping in the construction of West Qinling tunnel on LanzhouChongqing railway. The normal boring is simulated by means of TBM in tunnel section enlarged by drilling and blasting method, the organization of the material delivery trains is optimized and the invert segment installing machine is modified. In the end, the determination of the position of the sliding supporting frame, the supply of the construction materials and the invert segment installing efficiency are guaranteed, which ensures the efficiency of TBM secondary stepping. 

Key words: West Qinling tunnel, tunneling by TBM, stepping technology