Risk control - online deformation monitoring inside an urban TBM-driven tunnel using the tShape measurement system

The Swiss Weinberg tunnel was excavated from 2007 to 2011 using a tunnel boring machine (TBM). The railway tunnel is 4.8 km long and 11.2 m in diameter and mainly runs through hard molasse rock. 245 m before reaching the target shaft it transitioned to unconsolidated soft rock with only a few meters of overburden. Convergence measurements were required to mitigate the anticipated impact. As traditional convergence measurement methods were not a viable option, tShape was introduced for in-place deformation monitoring using SAA technology. Any deformation that moves the tShape array is accurately measured as a change in the shape of the array. Arrays were mounted on the inner lining right behind the TBM head. The web-based swissMon monitoring platform was used for automatic data acquisition, analysis and visualisation. swissMon determines transformation vectors using a 2D Helmert transformation. The transformation is applied relative to the centre of each of the measured points. Scale factor and rotation parameters can be either calculated separately or combined during the subsequent adjustment. This White Paper introduces tShape measurement technology and online data analysis. Based on the measurements taken at the Weinberg tunnel, it illustrates that even under difficult conditions tShape has proven to be a reliable system for automatic in-place deformation measurements inside tunnels.