Tunnels in Opalinus Clayshale - A review of case histories and new developments

Numerous tunnels have been built and new tunnels are planned in the Swiss Jura Mountains, and most of them intersect Opalinus Clayshale. This paper reviews several tunnel case histories which show that Opalinus Clayshale can be quite problematic by swelling during construction and also during operation, if the invert cover is not strong enough and if water can penetrate into the shale. Modern testing methods and a newly developed behavioral model based on these tests are then presented. They clearly show that Opalinus Clayshale when unloaded as can occur around the tunnel perimeter swells which in turn can induce creep and even failure. Considering this behavior in design and construction will reduce swelling and creep. Modern, TBM-based tunnel construction which utilizes prefabricated liner elements satisfies these requirements In. addition, the paper describes project management procedures that allow one to include the risks associated with swelling when assessing and awarding bids. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.