Pumping out

The pumping out indicates, by definition, the exhaustion of seepage waters mainly employed in the mines and mediums underground

For the Channel tunnel

The realization of a tunnel under the sea implies a perfect control of the seepage water flow: it is the essential condition of the success of the project. But this one passes by a certain number of precautions to take as a preliminary:

the choice of the geological layer tightest possible; chalk blue;
Of the Tunneller S and the Voussoir S designed to be adapted to the ground;
an installation of hopper before the execution of the surveys.

All these precautions are implemented during the digging of the tunnel, considering three origins distinct from makes of water:

leak-flows of the coating;
normal and accidental makes of water during work of excavation (in additional tunneller and work);
the collection of the industrial water used in tunnel.

The leak-flow of the voussoirs in tunnel corresponds to the level of sealing for which the coating was designed. It is thus equal to the final flow of infiltration of the coating, that is to say 5 liters a second.

The normal makes of water to the face, come from the leak-flow to the joints of tail of the tunneller, for a maximum pressure of work dimensioned as follows: - T1: 9 L/s. - T2 and T3: 15 L/s. each one - Tunnels Ground: 11 L/s. each one The accidental makes of water in gallery, in the principal tunnels, can come from the deterioration of a joint of the tunneller: • Side sea: 150 L/s. (10 bars of near. max.) • Side ground: 50 L/s. (3 bars of near. max.) For the additional work dug in opened mode, it was taken into account the possibility of a brutal increase in the makes of water, outputting 500 L/s. in railway tunnel under sea.

The flow of industrial water supply in tunnel (network sets fire to) is of 10L/s. by tunnel. Side ground, the digging of the tunnels is done in rising attack and the drainage in tunnel is done by gravity until the shaft bottom. Side sea, the attack is downward, except over a 2,5 km length. slightly going up (0,28%) beyond the first low point with the km No 8,7; it is thus necessary to go up water since the face to the well on uneven which can reach 67m. between the junction point and the stations.

The installation of pumping out is composed of 3 distinct parts:

the pumping out with face installed on the tunneller which pumps water since the face on approximately 2 km to the last relay station installed in tunnel;
the pumping out in tunnel installed progressively of 'advance which brings back water to the basin plug in shaft bottom;
the pumping out out of well which pumps water coming from the tunnels side sea and side ground since the underground of to at sea reject them by an emissary.

Each tunnel is equipped since the tunneller to the well with 2 independent installations:

for the permanent pumping out moving continuous;
for the pumping out of help. This line is used in the event of important accidental make of water or the permanent pumping out when this one is broken down or maintenance.

The pumping out with face is installed inside the skirt of the tunnellers, and must evacuate to the first station of relayage fixes the permanent and exceptional makes of water at face. Flexible devices on rollers ensure the connection between the following train and pipings in tunnels. Two pipings reject water in the first coffer dam of collection in tunnel where the station of head of the pumping out in tunnel is installed. Downward inclined, stoppings are installed in erasing all the kilometers approximately, with the right of the stations of relayage in order to create basins. Pumps submarines are installed in the artificial basins, like at the low point of the tunnels. These pumps feed, in parallel, a control of diameter of 200mm (maximum capacity 80 L/s) emerging in the following basin, side well, and so on. The starting of the pumps is ordered by gauges level high. In the same way, the stop is carried out by probes of bottom grade. Downstream from each pump, is installed a non-return Clapet to prevent the return by a pump to the stop, and line with the complete stop drains it. The pumping out of help of the tunnel of service consists of a control of 300mm. of diameter, equipped with pumps relay enters the station of head and the well. This line is able to take again the totality of the accidental flow of 150 L/s taken into account in tunnel of service.

The pumping out of help of the railway tunnels consists of 2 lines:

in each tunnel, a control of 400mm of diameter is equipped with pumps relay between the station of head and the well, of a capacity of 350 L/s;
the complementary flow necessary to evacuate the accidental flow of 500 L/s, taken into account in railway tunnel, is taken again on the level of the station of head by a control 300 mms in diameter. This flow is rejected into the other railway tunnel through the last bored branch.

The pumps relay are installed at the stations of relayage of the permanent pumping out; the pumps are sinkable and the switchgear is installed in height, which authorizes the temporary flooding of the pumps. Each pump can be isolated to allow the replacement or maintenance without stopping the operation of the line. Moreover, all the stations of head and resumption of coffer dams are equipped with a pump of replacement.

In shaft bottom, two basins plug of a full capacity of 3.500 m ³, collect water of pumping out of the tunnels side sea and side ground and are connected by a control supplying 4 mine pumps of the underground of of 325 l/s of capacity each one. Water of permanent pumping out is rejected at sea by a diffuser after passage in the station of treatment which makes it possible to reduce the suspended matter rate to 0,2 g/l for water charged 20 chalk fine g/l. The power supply of the installations of pumping out is ensured by the network priori: to conceal helped by generators of safety. The food of replacement of the installations of pumping out is ensured by the doubling of the circuits from post office EDF " Mandarins" and since the power station of help to transformers MT/BT feed of the pumps. These transformers and the electrical equipment boxes of the pumping out with face and the stations of relayage of the low point of the profile are tight; all the pumps are sinkable.

The operational safety is ensured by the existence of several independent lines of pumping:

in tunnel, in the case of breakdown of the permanent pumping out, the evacuation is ensured by the pumping out of help, by recovery in the coffer dam in low point, after overflow of the preceding coffer dams;
the presence of a piping putting in communication the pumpings out of the railway tunnels ensures a redundancy of 'pumping out of help.

Thanks to the doubling of the pumps on each line of pumping, the stop of a pump never stops the operation of a line. The whole of the installations of pumping out is controlled since the PCC where synoptic makes it possible to check the good performance of each component.

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