There are two types of water infiltration:
Recurrent infiltrations are caused by heavy rainfall or by an increase in the groundwater table, the underground surface where water saturation varies depending on the season and amount of rainfall. These two phenomenon can go hand in hand: when there is heavy rainfall above ground, the runoff flows into the water table through cracks, infiltrating the upper parts of our structures and trickling down from the ceilings.
- Situational infiltrations occur when modifications are carried out to surface infrastructure, such as roadwork or station repairs. Sometimes they are due to leaks in the water, sewage, or district heating networks. Major leaks damage the equipment in our transport system and are a factor in the creation of concretions. In other words, they contribute to the accumulation of various chemical and physical elements that eventually form a solid mass (like stalactites in a cave!)
Water infiltration? What does that mean?
To handle this problem, we have recourse to several different solutions:
Daily maintenance: when cleaning stations, we are able to notice the formation of any new concretions, as well as the progression of existing infiltrations.
Basic maintenance: a set of repair measures that are designed to halt the progression of infiltrations – such as resin injections, for example.
- Long-term maintenance: large-scale maintenance work that is heavy and intrusive by nature, such as the laying of drainage bands and watertight panels along tunnels or drainage systems, which are sometimes complemented by the installation of upper level water retention units.
Sometimes we need to apply in-depth treatments. In this case, we intervene directly on our stations. First, we dig down through the roadway to lay bare the structure. Then we waterproof the station from above by placing a watertight membrane over the structure. Although this treatment is effective for 50 years, the cost and complexity of its implementation mean that it has to be used sparingly!