Ceneri Base Tunnel

Project Overview

The AlpTransit Project is a massive rail project designed to provide more efficient rail freight routes via base tunnels through the Gotthard and Ceneri mountain ranges. Currently, freight trains traveling up the mountain ranges require pushing locomotives due to steep gradients. The base tunnels will provide a route for freight trains with minimum elevation gain and will shorten passenger train times between Zurich and Milan. Some route times, such as the trip between Lugano and Bellinzona, will be cut in half with the completion of the Ceneri tunnel. The Ceneri Base tunnels and the Gotthard Base tunnels will combine to create a new rail system that will span over 70 km (43 mi) of TBM-driven tunnels and 16 years of construction. The completed rail line is expected to open to traffic in 2019.

In April 2007, Contractor Consorzio Monte Ceneri (CMC) JV – a consortium of CSC, Lugano, Frutiger SA, Thun, Rothpletz, Lienhard + Cie, and Aarau, signed a contract for a 9.7 m (31.8 ft) Robbins machine to bore a 2.4 km (1.5 mi) adit on the Ceneri Base Tunnel Project. The completed adit tunnel joins up at approximately the halfway point of the main rail tunnels. The Main Beam TBM was completely refurbished near Milan, Italy where the cutterhead diameter was changed from 7.6 m (24.9 ft) to 9.7 m (31.8 ft). The TBM was the first machine on the AlpTransit project to utilize 483 mm (19 in) cutters, designed to offer a higher cutter load and longer cutter life resulting in fewer cutter changes. The refurbished machine previously bored successfully on the main headrace tunnel of the Kárahnjúkar Hydropower Project in Iceland.

Geology and Ground Support

Rock in the area consists of schist, Swiss molasse, and Ceneri orthogneiss with a UCS of 30 to 130 MPa (4,300 to 18,800 psi). Much of the tunnel was excavated under high cover of 600 m (2,000 ft). The geology of the tunnel alignment was good for TBM boring, with no squeezing ground or large water inflows encountered. New probe drills, designed in Robbins U.S. locations, were used to verify ground conditions ahead of the TBM. Temporary tunnel support including rock bolts, ring beams and shotcrete were also used depending on geology. Excavated material was temporarily stored at a lot onsite for later preparation as rock aggregate for concrete.

Tunnel Excavation

On November 6, 2008 excavation of the adit tunnel was completed on schedule after only ten months of boring. Only 30 cutter rings were changed during the last kilometer of boring, with the cutters excavating a combined 160,000 cubic meters (5.9 million cubic feet) of hard rock. Daily advance rates averaged 18.5 m (60.7 ft) – about 61% higher than averages achieved by similar machines boring the Gotthard Base Tunnel using 432 mm (17 in) cutters.