For shield-driven tunnels, particularly in subaqueous (below-water) regions, which lining material is most suitable due to its strength, watertightness, and ease of erection in segments?

Introduction / Context:
Shield tunnelling under rivers or water-bearing strata demands a lining that can withstand external hydrostatic pressure, provide watertight joints, and be rapidly erected as segments within the shield. Historical and contemporary practice has extensively used segmental metallic linings for such conditions.

Given Data / Assumptions:

• Tunnel is driven by shield method.
• Environment is subaqueous with significant groundwater/head.
• Key requirements: strength, watertightness, and segmental constructability.

Concept / Approach:

Cast iron segmental linings are bolted together to form continuous rings, offering high compressive capacity and tight joints using gaskets/caulking. They are especially suitable where immediate support and water control are critical during excavation.

Step-by-Step Solution:

Verification / Alternative check:

Case histories (e.g., early river crossings) used cast iron linings extensively, validating their performance under hydrostatic pressure and rapid segmental erection.

Why Other Options Are Wrong:

• Brick/stone: Permeable joints, slower construction, less suitable under high water pressure.
• Timber: Temporary support only; inadequate durability and watertightness.
• Concrete lining: Common in NATM or after initial support; cast iron excels in immediate watertight segmental installation in shields.

Common Pitfalls:

• Confusing final cast-in-place concrete linings with initial segmental support requirements of shield tunnelling.
• Underestimating joint watertightness needs in subaqueous conditions.

Final Answer:

cast iron lining