Tunnels lined with concrete formed on site are subject to ageing and developments that may endanger their stability, functions, safety and the required level of service. A certain number of defects are inevitably noted during or after tunnel construction. Moreover, depending on the age of the structure, construction methods and the pasage of time, a wide variety of defects may be obseved. In older, non waterprofed tunnels, water inrush is often at the origin of other defects.

Appropriate tunnel design work, correct construction procedures and best practice should make it possible to eliminate or minimise defects in lining work.