Excavation of parallel Gotthard road link begins 15 Apr 2021

Construction of a parallel tube for the existing 16.9km long Gotthard road link through the Swiss Alps is moving ahead with procurement of contractors to excavate the 12.7m o.d. tunnel expected to begin later in 2021. Running 70m to the east of the existing road link, excavation of the parallel tube is designed to be by mostly by TBM with two sections of drill+blast through difficult fault zones conditions.

Southern entrance to the existing Gotthard link
Credit: Grzegorz Święch (under Creative Commons 3.0 license)

Plans for a parallel road tunnel at the Gotthard have been long discussed with the existing bi-directional two-lane tube opening in 1980 (Fig 1). A fatal accident in 2001, in which two trucks collided, furthered the debate, but it was not until 2016 that a parallel tube was approved by Swiss voters with planning approval granted in 2019. Total cost of the project is estimated at CHF 2 billion (US$2.2billion) and the new tube is scheduled to be completed in 2029. When completed, traffic will initially travel bi-directionally through the new tube to allow closure of the existing tube for refurbishment. When both are opened, there will be one lane of traffic through each tube for each direction with a full-length hard shoulder lane in each.

Excavation of the parallel tube is divided into four contract packages: one for TBM excavation of the northern 7.9km, the second for TBM excavation of the southern 8.3km, and two access adits to permit open face excavation through the fault zones that caused significant problems during excavation of the existing tube in the 1970s (Fig 2).

Fig 1. New parallel alignment for Gotthard road link

Fig 2. Alignment under the mountains with two significant and known fault zones

The two TBM access adit contracts were awarded recently. A 4.1km x 7m o.d. drive to the northern fault zone between the Aarmassif and Urseren Zone is to be excavated by gripper TBM by the Webuild-Implenia-Frutiger JV in a contract worth CHF 86.5 million ($94 million). The package includes drill+blast excavation of a 150m long x 18m wide x 16m high cavern to house a concrete batching plant for progressing the heading through the fault zone.

Under a CHF 72.2 million ($78.6 million) contract, the Marti Tunnel-Mancini & Marti-Ennio Ferrari JV will excavate the 4.9m x 7.4m o.d. southern access drive to a fault zone within the Gotthard Massif using single shield TBM with a precast concrete segmental lining.

TBM excavation of the main roadway headings from the north and south portals will begin once the construction teams are confirmed.

Within the main 11.8m i.d. cross section of the TBM drives of the main parallel tube, the road envelope will be 4.8m high, with two 3.8m wide lanes plus a 1.5m wide pavement each side and a drainage channel (Fig 3). The invert will be used for utilities and water supply for fire management and the crown will incorporate the ventilation air intake and exhaust ducts that will be connected to five new drill+blast ventilation caverns of 50m long x 14m wide x 12m high. The caverns will connect to existing ventilation shafts via new adits of between 30m and 100m long. Construction of the ventilation infrastructure is included in the main construction contracts, three caverns in the southern package and two in the northern package.

Cross passages of 25m long x 4m wide x 3m high will be constructed every 250m to connect to the existing service tunnel of the operating two-lane bi-directional road tunnel. The total 68 cross passages along the route will include six that are of vehicle access dimension (Fig 4).

Following opening of the second tube in 2029, refurbishment of the original tube will take a further three years and will include renovation of the intermediate ceiling and complete replacement of the electromechanical equipment. Both tunnels are expected to be in operation by 2032 when the two lanes in each tube will provide for one lane of traffic and a full-length hard shoulder to improve safety and reliability.

Up to 7.3 million tonnes of muck is expected to be produced during the parallel tube excavations, much of it to be recycled including to underground a 1km stretch of the existing highway through Airolo. Muck will also be used for repair of the first tube and as part of the restoration of the shoreline of Lake Uri. It will be removed by conveyor belt to the portal sites and transported to a material processing plant at Stalvedro, south of Airolo, by rail from Göschenen along the existing SBB mountain rail line. Procurement of the materials management and logistics contract is underway.