ABSTRACT:

In preparation for the construction of a new underground facility at CERN, a programme of 3D finite element analysis was carried out to assist in assessing the feasibility of constructing the complex series of interconnecting caverns, shafts and tunnels. The paper describes the rock mass characterisation processes and the parameters assumed for analysis, plus summaries of the modelling carried out and the results obtained.

RESUME:

Pour preparer pour la realisation des structures nouveaux souterrain à la site CERN, on a fait une programme de "3D Finite element analysis" pour verifier la praticabilite de la construction tres complexe des cavernes, puits et tunnels. Rapportes ici sont les precedes de classification des rocheux, les va leurs calcules pour faire l'analyse, et un sommaire des analyses.

ZUSAMMENFASSUNG:

Fuer die Vorbereitung des Baus einer neuen Untergrundeinrichtung bei CERN wurde ein Programm zur 3-D finiten-Elemente-Analyse eingesetzt. Es wurde fuer die Abschatzung der Machbarkeit der zu bauenden komplexen Folgen von miteinander verbundenen Kavernen, Schachten und Tunneln verwendet. Beschrieben wird der Prozeß der Charakterisierung der Gesteinmassen und die fuer die Analyse angenommenen Parameter. Zudem werden Zusammenfassungen der Modellierungen und der errechneten Ergebnisse vorgestellt.

INTRODUCTION

The European Laboratory for Particle Physics, CERN, arranges collaboration between European countries in the field of high energy physics of a purely scientific and fundamental character. The organisation is formed by 19 member states. CERN facilities are located on both sides of the French - Swiss border, just outside Geneva. The facilities cover an area of around 10*10 kilometres and consist of more than five hundred surface buildings as well as an extensive network of underground structures including shafts, tunnels, galleries and large caverns. The organisation has recently obtained approval for the construction of a new particle accelerator termed the large Hadron Collider (LHC). This will be constructed in and adjacent to an existing, 27 kilometer long, quasi-circular tunnel which currently houses the Large Electron Positron Collider (LEP). The construction of the existing facilities has been described by Panet and Leblais, (Ref 1). Although much of the existing civil engineering infrastructure will be utilised for the LHC, a substantial number of modifications will be required. These major civil engineering works will include the construction of two very large caverns and several kilometres of new tunnels and galleries. In addition, several new shafts will be required with diameters up to 29 meters. These will be constructed through sands, gravels, silts and weak sedimentary strata. New surface buildings will also be required at many locations, ranging from small buildings for shaft access to very large industrial buildings in which experimental detectors will be assembled before being lowered underground. The current, estimated construction costs for these new civil works is in excess of 300 million Swiss Francs. Much of the new civil works will take place on the French side of the CERN site, with a certain amount of construction required on the Swiss side. This paper reports on a programme of 3D finite element analysis carried out to assess the feasibility of constructing a complex arrangement of underground openings at one particular location on the circumference of the quasi-circular LEP tunnel (Point 1). The existing facilities at Point 1 comprise the beam tunnel, two localised enlargements to the beam tunnel, a cavern offset from the beam tunnel with a tunnelled connection to the two enlargements, and twin shafts to surface. CERN's proposals for the LHC Project allow for the excavation of two additional caverns (roughly 34m and 20m span) and two new shafts to intersect the roof of the larger of the two new caverns (USA 15) at close proximity to the two existing shafts and tunnels.

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