Tail Seal Brushes and Grout: Stopping Water Ingress at the TBM Tail

Tail sealing is the TBM's last line of defence against groundwater. In water-rich sands, gravels and fractured rock, three or four rows of wire-brush tail seals, packed with injected grease, must hold back the head difference across the shield tail while backfill grout fills the segment annulus. When that barrier leaks, the consequences compound quickly: saturated muck, screw conveyor surging, face pressure instability, surface settlement and erosion of the grout ring.

Discipline matters as much as hardware. Grout should be pumped at a pressure that tracks — and slightly exceeds — measured annulus and groundwater pressure, with injected volume checked against theoretical tail-void volume on every ring. Continuous annulus pressure monitoring turns sealing from a guess into a trend. Operators should also watch grease consumption: a sudden rise usually means a brush is worn, misaligned or damaged, not that more grease is the answer.

Across Latin American metro and water tunnel programmes, volcanic and sedimentary mixed ground makes that monitoring harder, because permeability and abrasiveness swing from ring to ring. Keeping spare tail seals, brushes, grease and grout-line components on site is what stops a sealing problem becoming a stoppage. OUSUN, based in Deyang, Sichuan — China's largest TBM industrial cluster — supplies interchangeable tail seals, brushes and TBM spares with roughly 2–4 week lead times. tunnel-boring.com; [email protected].