PREDICTED AND MEASURED PERFORMANCE OF THE 62-M SPAN NORWEGIAN-OLYMPIC-ICE-HOCKEY-CAVERN AT GJOVIK

The feasibility of excavating caverns of very large span for underground siting of nuclear power stations in Norway was investigated in the early 1970s. In the end, the 1994 Winter Olympic Games provided the necessary impetus for utilizing a very large engineered rock cavern and proving its general feasibility. The 62m span Olympic Ice Hockey Cavern was constructed in Gjovik by Veidekke-Selmer JV in 1991. It is located in a jointed gneiss of average RQD = 67%. The Q-values range from 1 to 30, with a weighted mean of about 9, i.e. fair quality rock. The cavern has a rock cover of only 25-50m, thus posing challenging design problems. The investigations prior to construction included two types of rock stress measurements, cross-hole seismic tomography, geotechnical core logging, Q-system classification and numerical modelling with UDEC-BB. Predicted maximum deformations were 4-8mm; these were surprisingly small due to the high horizontal stresses recorded. Extensometer (MPBX) installations from the surface prior to construction, precision surface levelling and MPBX installed from inside the cavern gave a combined measure of maximum deformations in the range 7-8mm with the 62m span fully excavated and three adjacent caverns for the Postal Services also completed. Permanent rock reinforcement based on the Norwegian method of tunnelling (NMT), consisted of 10cm wet process steel fibre reinforced shotcrete, and systematic bolting and cable bolting in alternating 2.5 and 5.0m c\c patterns. Both the cables and bolting were untensioned and fully grouted.