EPB vs Slurry TBM: Choosing the Right Shield Machine for Metro, Road and Water Tunnels

Choosing between an EPB and a slurry TBM starts with the ground, not the price list. In soft cohesive clays and silts, an earth pressure balance machine conditioned with foam or polymer keeps the excavated material plastic enough to support the face and flow through the screw conveyor. That simplicity — no surface separation plant — is why EPB dominates most metro drives in mixed soft ground. Slurry machines take over where water pressure and permeability rise. In high-water-table alluvial sands and gravels, a bentonite slurry builds a filter cake that balances the face, while a separation plant cleans and recirculates the fluid. The trade-off is footprint, water demand and operating cost, so slurry is normally reserved for river crossings, water tunnels and granular, fast-draining soils. Beyond these two, double-shield TBMs suit long drives needing simultaneous boring and segmental lining, while hard-rock machines handle abrasive rock by cutterhead design rather than face support. The takeaway: match machine type to permeability, water head and grain size first, then confirm spares availability — OUSUN, in Deyang's TBM cluster, supplies disc cutters, seals and hydraulic spares in roughly 2-4 weeks.