With the excavation of the two 60m deep access shafts now complete, construction of the 1380m² UX15 detector cavern on Package 01 of the massive CERN particle accelerator project in Switzerland is due to begin.
The two shafts, PX14 and PX16, with a diameter of 20.5m and 14.5m respectively, have been excavated by contracting JV Porr Asgag Tunnelbau/C Baresel/ Zschokke Loche. The vault of the UX15 cavern, which will house CERN’s 7000 tonne ATLAS detector, will be excavated by the JV from five headings before two benches are dug out to reach the crane beam level.
Work below this level can only be started after the existing LEP beam tunnel, which passes through the planned location of the UX15 cavern, has been shut down in October 2000. The concrete vault lining will be cast and pre-supported with 200 tonne working load anchors before bench excavation proceeds.
Meanwhile, excavation of the USA15 technical cavern (23m span, 338-550m² cross section) is ongoing from the base of the existing PX15 shaft. Support comprises fibre-reinforced shotcrete and 9m grouted bars.
Excavation is being carried out using Liebherr 954 and 944 excavators with chisel hammer, roadheader and bucket attachments.
Design and site supervision for Package 01 is performed by a JV of Knight Piésold/Electricite de France.
Elsewhere on the project, Package 02, designed by a JV of Gibbs/SGI Ingenierie/Geoconsult, suffered initial difficulties with ground freezing due to the thick moraine sequence encountered. Contracting JV Dragados/SELI has overcome them and excavation for the two shafts (20.4m and 12m diameter) is now proceeding. The shafts will access two large caverns (26.5m and 18m span respectively) which will house technical equipment and the 14 500 tonne CMS detector. Excavation is due for completion later this year.
The final Package, 03, has been designed and supervised by Brown & Root with Intecsa and split into two smaller contracts. Package 3A, under construction by JV Taylor Woodrow/AMEC/Spie Batignolles and Package 3B by Prader/ Losinger Sion/Scrasa. Work includes construction of the PM12 shaft (12m x 18m) and the PGC8 shaft (8m dia.), which are completed, and ongoing excavation of two 3m dia. injection tunnels.
The 2.6km long TI 2 tunnel is being excavated with an Alpine roadheader and the 2.3km long TI 8 tunnel with a Robbins TBM. These headings are scheduled for completion in 2002.
After the civil works, installation of the LHC machine and the experimental detectors is expected to be completed by mid-2005.