TBM Tail Sealing in Water-Rich Ground: Brushes, Grout and Annulus Pressure

The tail of a shield machine is its most exposed interface: a moving steel cylinder passing a ring of segment lining, with an annular gap that groundwater is only too willing to exploit. Sealing that gap is not a single component but a system — typically three or four rows of wire brushes forming grease chambers, charged with fibrous tail seal grease that must hold pressure while segments advance. In the high water table alluvial sands and silts now driving metro expansion across South Asia, this system separates a dry tunnel from a flooded one.

Two variables decide whether the seal holds. First, annulus grout: pressure at the tail void must offset local hydrostatic head without fracturing the surrounding soil, so grout pressure and take are logged continuously against the theoretical void. Second, grease discipline — chamber pressure and consumption per ring expose brush wear and leakage paths before water appears. Rising grease consumption, falling chamber pressure or grout returns at the screw conveyor are early warnings that a brush row is failing.

The takeaway for engineers and buyers is that tail sealing is a consumables and monitoring problem as much as a design one. Brush sets, tail grease, segment bolts and hydraulic seals must arrive at ring-cycle speed; a machine idling for a valve or a brush ring costs far more than the part. OUSUN supplies TBM tail seal brushes, seals and spares factory-direct from the Deyang cluster, with typical lead times of two to four weeks — [email protected].