CERN AC Note (2000-03)-General description of the CNGS Project

4. Civil engineering

4.5 Use of explosives

The use of explosives is strictly regulated both in Switzerland and France. As in the case of the civil engineering works in the Geneva valley plain for LEP, CERN will keep the use of explosives to a strict minimum. At the same time their use cannot be completely ruled out as certain construction work cannot otherwise be carried out. Only in case of absolute necessity will CERN authorize their use on the CNGS project. In such circumstances, the blasting plans that must be drawn up by the firms will be submitted to a licensed laboratory for approval.

4.6 Construction techniques

4.6.1 Temporary access shaft

This 8 m diameter shaft is will be excavated using hydraulic rock-breaking techniques, or by blasting, if absolutely necessary. The walls of the shaft will be protected and shored up by anchoring systems and shotcrete. It will not be finished with in situ concrete. When the work is completed the shaft will be covered by a concrete cap so that it is guaranteed to be completely safe and so that it blends with its surroundings.

4.6.2 Tunnels

These can be dug by using either road header boring machines or by full-face tunnelling machines. The choice will be up to the contractor. The tunnels will be shored up provisionally as work advances by using rock bolts, whose function is to reinforce the rock mass and lock together separate rocks, in combination with shotcrete strengthened by welded mesh or fibres. For the proton beam tunnel the shoring phase will be followed by inserting an internal lining poured on site with a watertight system. As the decay tunnel will subsequently have a steel pipe inserted into it only the temporary shoring will be erected. Finally, in the remaining tunnels, once shoring work is done, a layer of shotcrete will be applied.

4.6.3 Chambers

These will either connect the different underground structures or be used to install the technical equipment. They will be dug out using road header boring machines. As the excavation progresses, the workforce will be protected and the walls consolidated by anchoring, structural steel, shotcrete or other relevant techniques. The finishing will be done by conventional methods using shuttering brought to the work-site from the surface.

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