Grand Paris Express, freezing monitoring station Vert de Maisons

The station Vert de Maisons (Maisons-Alfort), a station on the RER D, is one of the four stations on line 15 Sud of the Grand Paris Express lot T2A. During the excavation of the lateral access tunnels to the platforms, the Sables de Beauchamp are crossed, a water-bearing formation with high pore water flow rates. The new underground tunnel at the station must also be constructed with freezing measures, as the vault is in the Sables de Beauchamp.

Installations and instrumentation

192 freezing boreholes were drilled in the Sables de Beauchamp and in the underlying formation, the Marnes et caillasses. To control the freezing, Solexperts installed 500 temperature sensors to observe the following areas:

The temperature of the brine circuit (- 30 °C at the entrance)
The temperature at the interface between the terrain and the diaphragm wall
The temperature distribution in the frozen rock in specially drilled observation boreholes

The sensors are distributed over all frozen areas on four levels of the station. They are interrogated hourly by an automated control centre on the surface.

Visualisation and alerting

The hourly recorded data is sent to a web platform where it can be accessed and displayed in various graphical formats. When defined threshold values are exceeded, an alarm system is activated and SMS and e-mail messages are sent.