6. Water drainage

The purpose of a drainage system, which must be included in the design of the structure, is to ensure :

• rapid drainage of rainwater to prevent flooding of the roadway;

• protection of the structure from water infiltration, with varying levels of harmful agents.

The rainwater drainage system is essentially made up of gargoyles placed every 20 m or so on either side of the roadway or railway platform (figure 18 ). They collect surface water from a roadway, which is usually roof-shaped (for a two-way roadway) with two 2.5% slopes, or with a single slope (for a one-way or two-way roadway) of the same value. Water can be evacuated without special...