CNGS: Le faisceau de neutrinos du CERN vers le Gran Sasso.

3. Underground structures

All civil engineering work for the CNGS project is underground. 1000 m of the tunnels and the access shaft are to be built in France, with the remainder in Switzerland (see Figure 10 on page 20 and Figure 11 on page 21):

Table 2: Underground structures

Structures	Length or diameter (m)	Width or diameter (m)	Height (m)	Volume excavated (m3)	Volume of concrete to be poured (m3)
Temporary access shaft	8.0	_	57.0	3400	450
Access tunnel	769.0	3.1	_	8100	2250
Proton beam tunnel	590.0	3.1	_	6300	2300
Target chamber and annexes	_	_	_	_	_
Target chamber	115.0	6.5	_	5500	2060
Service tunnel	148.0	3.4	_	2100	900
Associated structures	_	_	_	2700	1100
Decay tunnel	992.0	3.1	_	11150	1550
Hadron stopping chamber	26.0	6.0	_	1100	250
Connection tunnel to LEP/LHC	355.0	3.1	_	3950	1250
Second muon detection chamber	3.5	6.0	_	200	90
Total	_	_	_	44500	12200

3.1 The temporary access shaft

This shaft is needed so that the civil engineering work does not interfere with works for the LHC. The shaft will have a diameter of 8 m and a depth of 57 m, and will be situated 130 m from the existing cavern ECA 4. It will be used only during the construction period. The excavation will be protected by shotcrete. Once the project is completed, the shaft will be covered by a concrete slab, and then topsoil so that the surroundings revert to their initial state.

3.2 The access tunnel

This tunnel will connect the existing cavern ECA4 to the target chamber. It will allow equipment and personnel access from Point BA4 of the SPS accelerator. Its length will be 769 m with an internal diameter of 3.10 m. The walls and ceiling will be shotcreted. The general slope of the structure will be 2.2%.

3.3 The proton beam tunnel

This tunnel will link the existing cavern TJ8 to the target chamber. It will be 590 m long and it will have an internal diameter of 3.10 m. The walls and ceiling will be of concrete poured "in-situ". The general slope will be 3.5%.