Abstract:

The constructioninduced upfloating of shield tunnel on South Changsha Railway StationGuangda Station Section of Changsha Metro Line No. 4 needs to be rehabilitated. As a result, the replacing technology of defective shield tunnel segment by composite lining is proposed according to the environment and geological conditions. (1) After route fitting by measured data, the defective shield tunnel length is about 40 m, and segment should be replaced reaches 25 (from ring 223 to 247). (2) The replacing technology of defective shield tunnel segment by composite lining is the best choice according comparison results among different replacing technologies by fuzzy comprehensive evaluation method. (3) The displacement and stress variation of ground and segment is studied by finite element method when dismantling ring by ring; and the results show bad situations, i.e., increase of vertical displacement crown top of surrounding rock, connected plastic zones of crown top of surrounding rock, increase of vertical displacement toward tunnel inside and horizontal displacement toward tunnel outside at segment adjacent to ring 1, compression of segment and increase of bending moment and axial force of segment, etc; which indicates that the segment dismantling number should be strictly controlled. (4) A new kind of movable trolley and its relevant construction technologies are developed and put into application to guarantee the safety of the tunnel structure and rapid construction.

Key words: metro, shield tunnel, upfloating, composite lining, segment replacing, fuzzy comprehensive evaluation method, movable trolley