Abstract: Maximum vault settlement, plastic zone volume, maximum shear rock stress and maximum axial force of bolt etc., are determinant factors which reflect the stability of tunnel group with small clear distance. To investigate into the correlation degree among these factors, we obtained the values of these determinant indexes by using finite difference software together with modified Drucker-Prager model. Dunhua road station of Qingdao metro is taken as engineering background. In line with fuzzy grey relational theory, the order of determinant factors and the optimum scheme of construction sequence are analyzed. Results reveal that maximum axial force of bolt can be taken as the primary determinant factor of tunnel group stability; while maximum vault settlement and plastic zone volume could also reflect the tunnel group stability significantly; maximum shear rock stress has the smallest influence on tunnel group stability. In the present study, scheme 4 and scheme 5 are concluded as the optimum construction sequences, and both are verified by equivalent stress analysis.

Key words: tunnel group with small clear distance, stability, determinant factor, fuzzy grey relational analysis, optimization selection of schemes