Gottard road tunnel – 2nd tube

The first Gotthard road tunnel with a length of 17km has been in operation as a national road link between north Switzerland to the south, the canton of Ticino, since 1980. In order to ensure the functionality and safety of this important transport axis through the Alps, the first tube needs to be extensively repaired, which requires a full closure. In 2012, the Federal Council decided in favor of building a second tube in order to then renovate the existing tube. To build the new 16.9 kilometer long second tube, two tunnel boring machines will be used for almost the entire route. Tunnelling with blasting is only necessary for short sections. In the north part of the tunnel, that is excavated in a rather short distance from the existing one, Huggenberger with the supplier Sisgeo, was awarded to supply geotechnical instruments for monitoring the excavation pit at the start of the tunnel and for monitoring the drill and blast part of the tunnel portal.

Huggenberger with Sisgeo supplied to the client the system for monitoring the forces in the struts that support the start pit, located in the vicinity of the old tunnel and other existing important infrastructure. For monitoring the struts, vibrating wire strain gauges (arc weldable type) have been welded to the circular 700mm diameter struts. Date transmission and data acquisition was realized using the WRLog system with LORA-technology (LORA long range radio based data transmission). The tunnel excavation near the northern tunnel portal is supported by pipe umbrellas. To monitor stability of the support method, horizontal BH-Profile type in-place inclinometers have been installed and with ongoing excavation, successively relocated to the tunnel face. Huggenberger was and is strongly involved to support the client and the clients service providers, for geotechnical monitoring (Monitron AG and Geoteam AG) for installation and operation of the systems.

Stability of the excavation pit but also of the tunnel excavation within challenging geotechnical formation and in the vicinity of important existing structures as the old Gotthard road tunnel, the Gotthard railway line but also service as power line and important regional roads, require high class instrumentation and a high quality support, that Huggenberger and Sisgeo could provide.