The idea to build these unusual repositories dates back to 1986, when the company Boliden decided to store environmental waste in man-made underground spaces. The dimensions of the caverns will reach 65 m in height, 30 m in width and 250 m in length. It will be 400,000 m³ of irregular shaped open space with various angles in profile, which is several times larger than the volume of the HVAC plant of the Prague Blanka tunnel, one of the largest underground structures in the Czech Republic. In total, the construction workers in Norway will have to extract 900,000 m³ of rock.
The first caverns to be bored reached a volume of 50,000 m³, and gradually the required volume of caverns grew with production and the need to store more waste. Together with the previous two, the currently bored caverns will be the largest of their kind in this underground system.
We are creating a complicated maze of tunnels divided into two levels with an average elevation change of 70 metres. Due to what is known as engineer's beam theory, the rock stress is distributed on the pillars between the open spaces. The construction requires good geological conditions, which fortunately exist in Norway. The underground system is in many ways comparable to conditions in a mine, but the character and profile of the work is more like a conventional tunnel," said Anton Vido, project manager for Metrostav Norge.
His team tunnels with the standard drill and blast method, which is most commonly used in Scandinavia. While the principle of the work is comparable to tunnelling, the concept of the activities and the development of the project are completely different. "We are facing much more challenging logistics and variability of work, as we have to adapt to the already established underground space and plan operation over two height levels. While a tunnel is a linear underground work that is excavated in a cyclic process, the spatial works are built by a combination of horizontal and vertical excavations that run in levels from the top of the cavern downwards," explained Anton Vido.
The construction work also includes three access tunnels and one smaller cavern with a volume of 22 700 m³, where there will be a secure space like a sarcophagus for mercury storage. 20 project team members and 68 construction workers are working on the project in four shifts.
"The the huge volume of mining, and also the pouring of rock directly into the sea make this quite a unique project. For these purposes we use huge floating pontoons with dimensions of 90 m x 45 m x 6 m. In short, the project is a huge challenge for us in many respects, all the more so as it is the first time that our company is the main contractor in the tunnel sector and has to demonstrate sufficient stability and self-sufficiency. However, we are ready for this challenge in all aspects," added Anton Vido.
The investor, Boliden, is an international company operating in various sectors around the world. They are involved not only in zinc production but also in other mineral commodities.
The Metrostav Group, which represents the largest Czech construction company, has been operating in Northern Europe since 2006. Since then, it has completed 15 projects, including the Helsinki Metro tunnels, the unique Salmon Road Bridge in Norway and the longest road tunnel in Iceland. In total, more than 48 kilometres of tunnels have been bored in Scandinavia so far. Currently, foreign contracts account for 40% of the Group's turnover. Last autumn, for example, tunnelling started in the Faroe Islands in parallel with construction in Norway.
Contact Details
Radim Mana
Metrostav Group Spokesman
Metrostav a.s. Koželužská 2450/4 180 00 Prague 8
T: 266 019 715, M: 601 110 376
radim.mana@metrostav.cz
