Risk Reports Bolster Floating Tunnel Project

Ramboll has issued two risk reports relating to Norwegian plans for an innovative new floating tunnel. Both reports have reached very positive conclusions, and have been taken as an encouraging step in the progress of the project.
The idea is to build a submerged floating tunnel just over 2.5 miles (approx. 4.1km) in length, which will make it significantly easier to cross the Sognefjord. With a depth of 1,309 metres and a length of over 126 miles (203km), the Fjord is an especially difficult crossing at present. Things are further complicated by the heavy amounts of shipping traffic that make use of the fjord’s waters. The new tunnel is planned to open up much easier crossing without the use of ferries. Other fjord crossings, such as the E39 motorway route which runs between Stavanger and Trondheim, will be easily accessible to users of the tunnel, making it much easier to traverse this part of Norway by car.
Analysts at Ramboll concluded in the reports that a collision that could cause the collapse of the tunnel is vastly improbable. In fact, it is so unlikely that it could not reasonably be expected to happen within 10,000 years. According to the reports, which Ramboll produced on behalf of Norwegian public roads authority Stratens Vegvesen, submerged pipeline bridges such as the one proposed get struck by ships once every nine years. However, this figure is mostly made up of minor incidents, and includes occasions when the bridge is only brushed by ships. It also includes incidents where small craft bump into bridges causing little or no damage. The possibility of a serious collision is much lower, and the chance of the bridge collapsing as a result is negligible.
The report used models based on volume of ship traffic, the probability of a ship losing control while on a collision course with the bridge, and the likelihood of it failing to regain control before impact. As well as the relatively low chance of this happening in a way that would criticaly harm the bridge, elements of the tunnel’s design also mitigate the risk. A deliberate “weak link” is designed to be destroyed and float off in the event of a severe impact, leaving the car-carrying section intact.
The reports also examined whether other possible problems could cause serious issues for the bridge, such as anchors or engine failures. The results were positive and encouraging across the board, suggesting very low levels of risk associated with the project.
Now the reports have been completed, the feasibility assessment stage of the project has been completed. This will now be followed by the final concept study, which is due to begin in the near future.
The bridge is intended to significantly simplify travel in the area, but it comes with a number of engineering challenges. According to the manager of Ramboll’s risk and safety department, Søren Randrup-Thomsen, ” a pipeline-bridge is a complicated construction. It is difficult to anchor on the bottom because the Sognefjord is so deep and affected by currents, waves and buoyancy.” To combat this, the bridge will be stabilised by 16 floating pontoons.
Author: Matthew Scott