By Lars T. Thorbek, Global Division Director, Major Crossings
There’s no doubt that the construction of major crossings such as bridges and tunnels use a large amount of materials, especially steel and concrete.
A large bridge such as the Queensferry Crossing in Scotland for example spans a massive 2.7 kilometres and uses 37,000 kilometres of cabling – nearly enough to span the circumference of the Earth. But there are ways of making even these large-scale projects more environmentally-friendly and sustainable.
Less spillage better for the environment
Queensferry Crossing utilised caissons to significantly reduce spillage that can be hazardous to the environment and marine eco systems. A caisson is a prefabricated hollow box or cylinder that is sunk into the ground and then filled with concrete to form a foundation. This is highly preferable to direct dredging. The giant north and south towers of the Queensferry are founded on circular steel caissons 30 metres in diameter which were sunk to the top of the bedrock 50 metres below water level. A thick concrete plug was then poured underwater within the cylinders to enable the construction of a reinforced concrete base for the foundations towers.
Companies working on the bridge also has to fulfil certain requirements in regard to minimising their carbon footprint during construction. And pivoting the position of the bridge approaches helped saved nearly one hundred thousand tonnes of earth excavations.
Concrete is one of the main materials used in major crossing projects and the production of cement is not particularly environmentally friendly. That is why it is crucial for companies to find new, more sustainable methods of production. Ramboll, in collaboration with industry partners and universities, is currently involved in a major research and development project to find solutions that have a lower environmental footprint.
While new cement production techniques will take some time to come to fruition, in the short term many construction projects can also benefit from more stringent control over the amount of concrete they use. While it is important that concrete structures are designed to fulfil their function, they should not be over-specified - you should only make what is necessary and cutting down the use of material to a minimum reduces waste and has positive effects on the environment.
The durability and robustness of materials also play a part, with major crossings such as Queensferry built to last and designed to withstand constant use and extreme weather.
Sustainability of course is not just about the environment; at Ramboll, we see it in the broader context of social and economically sound solutions. In India, the planned Mumbai Trans Harbour Link, joining Mumbai with the satellite city of Navi Mumbai, will not just alleviate congestion and pollution, it will also play a crucial role in future growth in India, providing access to new jobs and housing for hundreds of thousands of people in the fast-growing Navi Mumbai. Similarly, the Fehmarnbelt tunnel between Denmark and Germany will reduce travel time and provide significant economic benefits across the region.
The movement of people and goods is essential to economic propensity and a well-functioning society and major crossings such as bridges and tunnels provide the means to do that. That’s why it is important to ensure that their design and construction is as environmentally, socially and economically sustainable as possible.