Field monitoring analysis of ground response induced by a large-diameter slurry shield tunnelling through upper-soft lower-hard strata at shallow depth: A case study of the Guanghua Intercity Railway

Shallow-buried large-diameter slurry shield tunnelling through upper-soft/lower-hard composite strata is highly sensitive to tunnelling parameters, making deformation control challenging. To investigate the characteristics of ground response induced by shield tunnelling, three monitoring sections were established in the launching section of Work Area 5 of the Guanghua Intercity Railway project, and field monitoring was conducted on surface displacement, subsurface vertical displacement, horizontal displacement (inclinometer), and pore water pressure. The results show that the disturbance influence zone is relatively large during tunnelling through such composite strata. The ground response exhibits distinct stage-dependent characteristics, spatial variability, and an asymmetric distribution due to stratum heterogeneity. Identifiable ground deformation was observed when the cutterhead was approximately five rings ahead of the monitoring section, and the most intense response occurred during the crossing stage. The subsurface vertical displacement was characterized by upper-layer heave, lateral outward displacement, and asymmetric distribution, while the surface displacement changed from settlement to heave and exhibited a W-shaped profile. Segment erection and shield tail passage induced local secondary disturbances, after which the ground response gradually stabilized. During the crossing stage, pore water pressure increased on both sides but decreased in the middle, and fluctuated cyclically with shield advance and stoppage. The dissipation of excess pore water pressure induced by grouting exhibited a lagging effect. Variations in tunnelling parameters significantly affected both the magnitude and extent of ground response, and higher advance rates resulted in greater deformation magnitude and a wider disturbance influence zone.