Sprayed concrete applied at the Landeck by-pass tunnel, construction lot north

The landeck by-pass tunnel is going to divert heavy transit traffic from the town of landeck. After long discussions construction started in 1997. By mid-2000 cars and lorries will pass through the tunnel, thus finally relieving the population of landeck of excessive traffic pollution. The project of the bypass tunnel was divided into construction lots south and north. The paper deals with the shortcrete method applied at construction lot north. Taking account of technological, operational, economic and also ecological considerations, a shotcrete system with wet aggregate and spray cement was chosen. For this method a new equipment developed by Ploderer and Parr was used: an automatic mixer system supplying three shotcreting machines, which is installed 50 m behind the working face and moved along as the excavation proceeds. The shotcrete mix is produced directly at the construction site. The shotcrete ingredients are fed into the mixer by means of a wheel-mounted loader (aggregate) and a bulk cement transporter (spray cement). The advantage of this system consists in having any quantity of shotcrete available at any rime as shotcrete ingredients can be supplied to the system also while the plant is in operation. In order to meet the quality requirements, an extensive quality assurance programme including qualification and quality tests was set up and implemented. The overall outcome was so positive that the method described, i.e in situ production of shotcrete in combination with wet aggregate and the corresponding spray cement SBM-FT, will continue to be used on a large scale.