THE SANGATTE SHAFT AND FOND PIGNON DAM
THE DESIGN AND FUNCTIONS OF THE SHAFT
The emblematic structure of the Sangatte shaft is the main access to the underground work site and allows the excavation of tunnels from a single intermediate starting point.
It consists of the shaft itself with a diameter of 55 m. and a depth of 65 m. and 6 stations extending over 50 m. on either side of this shaft.
The main functions of the shaft and stations are:
- To allow the elements of the tunnel boring machines TBM and the trailers of the
train following the TBM to be lowered and assembled.
- To ensure access to staff and the supply of excavation sites.
- To allow the supply and evacuation trains to be operated.
- To ensure the evacuation of the waste to the Fond Pignon depot using the bottom
of the shaft for the disposal and pumping facilities
To ensure the discharge of water and the supply of electrical power.
THE CONSTRUCTION OF SHAFT AND STATIONS
The tunnel starting points stations are built inside a huge vertical waterproof surrounding wall in bentonite cement in the shape of an ellipse of 200 m in length and 100 m in width.
After digging by excavators and evacuation of the excavated materials by trucks on a peripheral ramp, the concrete coating of the upper part of the shaft is made by successive rings of 2.50 m in height.
This work is stopped at the tunnel level to allow the construction of stations by traditional methods.
They are then re-started to perform the lower part of the shaft.
THE INSTALLATIONS AND THE EQUIPEMENTS IN THE SHAFT
Facilities and equipment are designed to make each tunnel-tube independent for its supplies and muck shifting, while providing for the ability to come to the rescue of another tunnel. They are sized to allow tunnel boring machines to work simultaneously at their optimal speeds.
The main equipment of the shaft is:
- 4 over Head cranes: 1x 430 t – 2×60 t -1×30 t
- 2 12-persons elevators and 3 7.5-t lifts
- 5 goods lifts each handling 3 wagons at a time
- 1 complex network of railway tracks with 80 switches/points
- 5 double shredders feeding 5 detainers
- 8 piston pumps feeding 8 push-back lines 250 mm in diameter up to the Fond Pignon Dam, with the flow of each line being 90 m3/h to 120 m. high and 1,600 m. away.
THE DAM OF FOND PIGNON
The Fond Pignon dam, designed by the Coyne and Bellier design firm, is built with compacted fill of white chalk obtained from the rights-of-way applicable to the current reservoir.
A significant dam of 1200 m long and 38 m in height is carried out in 3 successive phases as the TBMs progress.
At the end of the tunnel excavation, the volume of the deposit stored in the dam is 5.4 Mm3 excavated volume representing 3.1 Mm3 of chalk in place.
This dam of Fond Pignon has been the subject of specific measures to integrate into the local landscape after the work. For this purpose it has been carefully vegetated with selected species.
It is considered an example of industrial success in terms of ecology and the environment.