Abstract: This paper presents the finite difference analysis results using FLAC3D of the effect of Tunnel Boring Machine (TMB) excavation of the Changsha Metro No. 1 tunnel on the adjacent highway box culvert. By comparing the field monitoring data and the numerical analysis results, effect of the tunnel excavation on the active highway box culvert such as settlement in the longitudinal and transverse direction were investigated. The results indicate that, in the left side of the tunnel excavation, the “V” shape of the settlement at D1 cross section was observed and settlement influence zone is within three times of the tunnel diameters; During the excavation of the right tunnel, the settlement trough was becoming wider and a zone of settlement superposition at area between two tunnels was formed and the maximum settlement was 18.24 mm. The monitoring point near the center line of the left line had the largest disturbance when the shielded tunnel passed through. The rate of the settlement change decreased from 0.94 mm·m^-1 to 0.40 mm·m^-1 as the distance to the excavation face increased, which reflected in the soil settlement and deformation monitoring values. The monitoring points D1-5 in the middle area of the left and right lines were affected by the grouting diffusion effect of shielded tail, and the variation of soil settlement disturbance was not obvious. The settlement deformation of the highway box culvert did not exceed the control value, but the differential settlement was relatively large due to the influence of the consolidation of disturbed strata, slurry solidification and pore water pressure dissipation. It was suggested that the circular grouting of cement-water glass slurry method should be adopted in the future projects to reduce the settlement deformation.

Key words: shielded tunnel, highway box culvert, sleeve pipe reinforcement, settlement superposition, settlement rate