The environmental impact of rock support for road tunnels: The experience of Norway

Despite the high levels of investment in the construction of underground space, there has been relatively little research so far on the environmental impact of tunnelling and rock support. In an attempt to fill this gap, this paper explores and compares the environmental impact of rock support on road-tunnel design in Norway for different rock-mass classes and tunnel sizes. Norwegian rock-support practices in road-tunnelling over the last twenty years are used to estimate figures for the consumption of material, equipment and energy. The background data are drawn from various Ecoinvent databases and environmental product declarations for major materials. The results indicate: 1) that the global warming potential (GWP) varies from 1 ton to 3.6 t per meter of rock support for different tunnel sizes and rock masses; 2) that all the environmental impacts of the shotcreting (or concrete-spraying) process are significantly greater than of all other processes; 3) that when a tunnel becomes larger or the rock mass becomes poorer, the relative contribution of the bolting process will increase; 4) that all environmental impacts are more sensitive to rock-class than to cross-section parameters; and 5) that potential improvements include reducing rebound, better designs of shotcrete admixtures and binders, improving durability and mechanical properties, and implementing the GWP or other environmental indicators during the design and tendering stages.