The Brenner Base Tunnel is one of the largest infrastructure projects in Europe and will be the centerpiece of the Scandinavian-Mediterranean TEN-T Corridor from Helsinki to Valetta, Malta.
Project operations are ongoing and progressing well, as Karin Baeppler of Herrenknecht – the project’s TBM supplier – explained ahead of the Australian Tunnelling Conference.
But at 64km in length, with a unique geology, and comprised of two single-track rail tunnels with a service and drainage gallery in between, the project has not been without its engineering challenges.
“One of the most difficult and unique features of the project is an exploratory tunnel that bores right up the entire length and sits about 12m below and in between the main tunnel tubes, acting as a service and drainage gallery during operation,” Ms Baeppler said.
“The geology along the section is also very challenging due to the presence of quartz phyllite and shale and a high overburden of up to 1,300m.
“Rock mass behavior indicates loose to friable conditions, shear failure, or even squeezing rock behavior. These types of soft rocks and converging rock masses present unstable tunnel face conditions, with the potential for breakouts and collapses.”
Further complicating matters, the 15km-long section of the Tulfes-Pfons exploratory tunnel of the Brenner Base Tunnel section has a comparatively low overburden height – compared with the Gotthard tunnel project – and numerous fault zones predicted, making up around 19 per cent of the total distance of the exploratory tunnel.
Ms Baeppler explained this makes for an extremely demanding environment for TBM work.
The combination of these factors at the tunnel face has required increased rock support efforts and technology adapted to the complex conditions. “We have had to use a high degree of rock support work in the L1 and L2 area of the Gripper TBM,” she said.
In addition, Herrenknecht is using a well-adapted TBM concept to construct the 15km exploratory tunnel.
“Tunnelling started from Austrian Ahrental towards the Italian border in challenging terrain using a 7.93m-diameter Gripper TBM.”
Ms Baeppler said the use of an open Gripper TBM for the exploratory tunnel is based on tried and tested technology.
Gripper TBMs have already proven themselves in numerous complex projects in the Alps, including the Lötschberg and the Gotthard tunnels.
“Thanks to evolutions in this technology, we now also have systems in place that help to optimise tool maintenance intervals, such as the DCRM system and the DCLM system,” she said.
“These make it possible to draw conclusions about the nature of the tunnel face, allowing a kind of tunnel face scanning; in turn, having a positive effect on tunneling rates.”
Looking to the future, Ms. Baeppler said that the DCRM and DCLM, together with a newly developed camera system, will enable real-time preliminary exploration, further improving performance safety and quality and optimising the tunneling parameters.
“The knowledge we are gaining from driving this tunnel is contributing to the development of an optimal tunnelling and safety concept for the construction of the main tunnel”, she concluded.
Hear from Karin Baeppler at the Australian Tunnelling Conference, where she will talk more about how the use of complex TBM concepts is helping to overcome engineering and geology challenges in the ongoing tunneling project.