Longitudinal solution of the CERN sample site project, given as an example.

The conventional facilities and siting studies are currently organised in a global group within the GDE. Some specific studies, like civil engineering, are totally site-dependent and studied separately in each region.

In Europe, two sample sites have been proposed for the Baseline Configuration Document for the ILC, one at DESY (Germany) and one at CERN (Switzerland and France). These proposed sites benefit from past studies for LEP, LHC, HERA and from the TESLA Technical Design Report. (The ILC layout would follow closely the TESLA layout for the first 32.8 km.) The two sites particularly differ by the composition of the rock and soil underground. At CERN, the bedrock called "molasse" is rather stable and watertight, and dictates a deep tunnel configuration (around 120 metres). The Tesla underground, however, is made of damp sand for the majority, which is in favour of a shallow tunnel (around 20 metres). Because of environmental and technical constraints, the suggested layouts of the sites would be fixed at one end. Actual positioning of the interactions points would thus take into account the final length of the project (after a potential upgrade of the energy).

Jean-Luc Baldy

Environmental studies are playing a large role in the evaluation of the sample sites in all regions. "An environmental impact study is mandatory. We have given much attention to it from the start of the ILC Reference Design Report", said Jean-Luc Baldy, co-convenor of the Conventional Facilities and Siting (CFS) GDE group and head of civil engineering at CERN. For instance, because of the noise and vibrations generated to bore rocks, engineers may have to use quieter machines. "These tunnels would be built by a Tunnel Boring Machine (TBM). This kind of equipment has the smallest impact on the existing surface buildings and infrastructure and on natural environment", he said.

The proposed tunnel would stand underneath both inhabited and uninhabited areas, having direct impacts on the machine construction. "For example, for both European sites, careful attention will be given to the great quantities of spoil to be excavated. Whether we will eliminate or ‘landscape’ it, we will operate with the least possible disturbance to the present surroundings", said Baldy. Although the GDE will select the most efficient layout, the periodicity of the access shafts to the tunnel might also be in certain cases in contradiction with the surface environment. Engineers may have to shift them in the design or to add connecting galleries to access the tunnels. They must also evaluate the seismic activity of each site, though the impact is expected to be very low. For both sites in Europe, the group has mandated a common consulting company (previously mandated for the TESLA project) for their worldwide recognised underground technology expertise. These consultants will realise a preliminary design and subsequent costing. They recently visited the two sites to evaluate potential specific potentialities and difficulties.

Apart from civil engineering, some other aspects are being studied globally such as ventilation, water cooling, safety and fire fighting systems, survey and alignment, handling and electric equipments. Members of the global group are currently gathering all the information they need from the different GDE Area Groups to determine the size of the facilities, including diameters of the different tunnels, detector halls and dimensions of the required alcoves and access shafts. They have drawn a first schematic layout which was recently presented at the Bangalore Workshop and is being updated according to confirmed data received from the other Groups.

Last Version of the BCD for Conventional Facilities and Siting (.doc)

-- Perrine Royole-Degieux