Coo-Trois-Ponts Hydroelectric Power Station

Micropile technique

• 4 vents realized

• Ø 204, 142 and 90 mm

• 20.5 m deep

For once, we are using micropile technique to .. not make piles (!) but to drill holes:

At the Coo power station, during electricity production, the water is turbined from the upper basins to the lower basin through galleries and turbines, with a flow rate of up to a volume of 10 Olympic swimming pools per minute. ! We are drilling vents there to bring the galleries (connecting the units to the lower basin) to atmospheric pressure when emptying these galleries for maintenance work.
Considering the different layers to go through and the precision work required, we came up with a complex solution that could be achieved with a single drilling machine. We first drill through the rock using a down-the-hole hammer (diameter 204 mm), then we partially drill the reinforced concrete constituting the structure of the galleries using a tube equipped with a crown (diameter 142 mm). The borehole is then fitted with a tube and sealed. Finally, the last cm of reinforced concrete are drilled (diameter 90 mm) in order to open the vent.