The Brenner Base Tunnel - a new link through the Alps

21 During its construction the Brenner Base Tunnel must be continually surveyed because cavity deformations may occur. To do this, convergence bolts are drilled into the rock and possible movements such as subsidence, longitu- dinal or transverse movements in relation to the tunnel axis are acquired using mounted prisms. The result is shown in displacement diagrams that enable geotechnical engineers to evaluate the behaviour of the rock. Continuous monitoring The points of light, clearly visible in the photograph, are data points from reflectors that allow accurate measurements and inspections throughout the entire period of construction. A tunnel scanner can record millions of measurement points in the tunnel within a few minutes. This is neces- sary to check the size of the excavation. If different construction phases are scanned, for example raw excavation and shotcrete, this method can be used to check the thickness of the shotcrete. It enables the construction company to monitor compliance with the structural requirements. During the construction of the exploratory tunnel, the largest alignment error is expected between Mauls and Wolf, namely a lateral deviation of 22 centimetres. During the construction of the two main tubes the largest alignment error is likely to occur between Mauls and the Isarco river underpass, with a lateral deviation of nine centimetres The deviation in the construction of the main tunnels will be less, because surveying can be carried out via the shaft connections to the already completed exploratory tunnel. Tunnel scan Alignment accuracy Extract breakthrough structures Tunnel/shaft structure length [m] Standard deviation [mm] with reference to the tunnel axis transverse lengthwise high Innsbruck exploratory tunnel – Ahrental access tunnel 6,042 18 16 12 Patsch ventilation shaft 180 8 5 11 East connecting tunnel 9,609 47 38 13 West connecting tunnel 9,650 67 29 13 Emergency tunnel Innsbruck bypass tunnel 8,405 182 21 9