7.4. Tunnel drainage

Road tunnels are equipped with a drainage system to deal with surface water from portals, groundwater infiltration through the lining, wall washing water, spillages from a road tanker and fire fighting water.

Where the transport of dangerous goods is permitted, the drainage of flammable and toxic liquids is a key concern. Drainage is important to minimise the size of pools that may otherwise form in the event of a spillage from a road tanker. In the event of a spillage of flammable liquid, the drainage system can have a major effect on the size of a resulting fire.

Drainage systems typically consist of gulleys, channels, pipes, sump and pumps, oil/water separators and control systems for collection, storage, separation and disposal of effluent that might otherwise collect on the roadway. Some authorities specify the use of slot gutters in order to maximise drainage performance. Sump and pumps are generally provided at the portals and at low points.

The impact of water on tunnel construction and operations is discussed in Section Water impact.