The Kielder experimental tunnel: final results

The entrance to the Kielder experimental tunnel was sealed late in 1979 about the same time as the driving of the 32 km long 3·3 m dia. tunnel for the Kielder Water Scheme was completed. The experimental tunnel was the scene of quite detailed studies of the performance of a variety of support systems in the Four Fathom mudstone over a period of five years. The important lessons learned from these long-term experiments are reviewed. In particular the most recent experiment where the same support, consisting of an annulus of sprayed concrete, was placed at different times after excavation (equivalent to different amounts of rock yielding) is reported. This has enabled characteristic lines, or ground-reaction curves, to be established in the field. The strains and deformations in the cast in situ concrete lining, in a part of the Kielder main tunnel where it passes through the same mudstone, are also presented. These demonstrate that it is lightly loaded-a result to be expected from the experimental tunnel studies.