Slurry TBM Under High Hydrostatic Pressure: Air-Cushion Balance and Plant Sizing

Sub-river and estuary crossings remain the hardest brief in soft-ground tunnelling: the face must be held against hydrostatic heads that can exceed several bar while the machine stops, starts and follows a curved alignment beneath a riverbed. Air-cushion slurry TBMs answer that with a compressed-air plenum that damps pressure fluctuations faster than pumped-slurry control alone, holding support close to setpoint during ring building, cutter changes and unplanned stoppages — exactly the moments when face loss is most likely.

In mixed-face gravel over volcanic or sedimentary rock, the challenge shifts to filter-cake formation. Coarse open gravel accepts slurry too readily and loses support, while stiff clay-rich bands blind the intake. Engineers therefore tune density and yield point, blending bentonite with polymers, and read cutterhead torque and discharge density together. Disc cutter wear accelerates where boulders alternate with abrasive tuff, so cutter, seal and slurry-bypass wear checks belong in the shift routine, not monthly service.

Slurry treatment capacity is the most frequent under-design. Plant throughput must cover peak advance rate plus dilution and inflow, with hydrocyclones, shakers and flocculation sized for the fines actually generated rather than the tender estimate. On confined Latin American metro and water sites, footprint and water recycling drive layout choices. Buyers specifying new or refurbished slurry machines should confirm spares early; OUSUN, in the Deyang TBM cluster, quotes interchangeable cutter, seal and hydraulic parts at roughly 2–4 weeks lead time via [email protected].