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Abstract

Following in-ground shield docking, staged cutterhead removal progressively reduces face support in layered subsea ground, inducing stage-dependent stress redistribution and deformation around the tunnel opening. This study investigated the response of sand-over-tuff ground at the Jintang Subsea Tunnel using physical similarity tests and three-dimensional numerical simulations. Five cutterhead segments were removed in a fixed sequence, and the evolution of ground stress and displacement was evaluated at each stage. Removal of the top segment caused the greatest stress release and displacement increment above the crown. Subsequent removal of the upper segments extended the disturbed zone towards the shoulders, whereas lower-segment removal mainly induced local responses. Deformation was concentrated near the tunnel opening and in the upper half of the cross-section. The numerical model identified a collapse arch above the crown, with its inner boundary approximately 2 m above the crown and its outer boundary near the sand–rock interface. The model reasonably reproduced the stage-dependent displacement trend; the final vertical displacement at monitoring point 1# was 5.7 mm, compared with 8.9 mm in the physical test. These findings identify the critical removal stages and provide a stage-resolved basis for dismantling risk assessment under comparable unreinforced conditions.