Abstract
This article describes the construction experience of the Oslo tunnel, whose path cuts through several different geological formations. The tunnel is being excavated by conventional drill and blast techniques, despite the very strict vibration limits that have been specified. Purpose-designed charging and blasting techniques are being applied to keep ground vibration under control, and very sophisticated drill rigs are being used. The Norwegian geotechnical institute has coordinated the ground investigation, support design, and vibration monitoring on the tunnel. There have been extensive site investigations of the ground under the tunnel route, using seismic and acoustic measurements, core drilling and bedrock soundings. These surveys have provided excellent information about ground conditions above the tunnel and ahead of the face, and they have contributed to the design of the blasting and support systems. Numerical modelling has been used successfully to predict the effects of blasting on the pre-grouted sections of the tunnel. Nitro consult was engaged to design the blasting system to satisfy the requirements for extremely low ground vibrations. Experience indicates that this system can be applied to all tunnels under all conditions, providing a safe method of working and efficient use of explosives and detonators; ground vibrations can be restrained in a manner not previously considered possible. It was found in practice that all sections of the Oslo tunnel could be blasted full-face if required. (TRRL)
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