Abstract: In this paper, the shield tunneling process of Hefei Metro under 3 different strata conditions, i. e. soft soil, hard rock and composite strata, is simulated by geotechnical finite element software PLAXIS 3D. And then the influences of support force N of tunneling surface, shrinkage rate C caused by the taper of shield steel shell and grouting pressure p behind lining on surface settlement and deformation of surrounding rock are studied. The study results show that: (1) For the surface settlement, the stratum condition and burial depth have a greater limitation on N and p than that on C. (2) The impact of shield tunneling parameters (N, C and p) on surface settlement of soft soil layer is larger than that on surface settlement of composite strata. (3) The p has a significant influence on segment floating and internal force, which should not be overlarge; the soft soil layer is most sensitive to p, followed by hard rock and soft-hard composite formation. The study results are applied to the control of shield tunneling parameters in a section of Hefei Metro Line 4, and according to the fiel data analytical results, the shield tunneling attitude is correct, the surface settlement is stable, and the tunneling parameters are rational and feasible.

Key words: composite strata, grouting pressure, shield taper, tunneling face support pressure, shield tunneling parameters, metro tunnel, numerical simulation