Permanent drainage of tunnels: which measures are typically adopted to ensure long-term dry and durable operation of the tunnel and its lining?

Introduction / Context:
Water management is a defining feature of tunnel durability. Even small inflows can degrade trackbeds, pavements, or utilities and promote lining damage. Designers therefore combine multiple permanent drainage tactics to intercept, convey, and reduce inflow throughout the life of the tunnel.

Given Data / Assumptions:

• Tunnel through rock/soil with potential inflow.
• Goal: long-term drainage and watertightness.
• Available measures: longitudinal drains, open channel drains, linings, and pre/post grouting.

Concept / Approach:
Longitudinal drains collect seepage along the sidewalls or invert and take it to sumps. Continuous open drains provide redundancy and access. Concrete or segmental linings reduce seepage and protect the structure. Grouting seals discontinuities in the surrounding ground. Used together, these measures minimize pore-pressure buildup and protect the tunnel envelope and track/roadbed.

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