February 19 was the second anniversary of i the authorisation of construction of the Super ' Proton Synchrotron (SPS). It was celebrated by the start of tunnel boring by the "mole". This conventional Robbins boring machine, built in Seattle, came by sea from the US Pacific Coast, through the Panama Canal to Rotterdam, up the Rhine to Basel, and then by lorry to Geneva. It arrived at the end of last year. The SPS tunnel will be 4.8 m in diameter with a circumference of 6.9 km. A tunnelling scheme was selected (rather than the "cut-and-fill" method) to avoid changing the character of the countryside in a major way so that agricultural and forestry activities can continue much as previously. A second reason is the variation in altitude over the site. To retain a minimum Earth shield of 20 m for radiation protection, the tunnel will be 65 m below the highest point on the surface at an average depth of 40 m. A final point is that the molasse bedrock is solid enough to allow the tunnel to be bored reasonably easily.
展开▼
