SFR CONCRETE | LINING
NEW APPROACH FOR SFRC FINAL SUPPORT AND LINING
A new approach to improving the use of sprayed concrete for final support and lining is discussed by Benoit de Rivaz, Global Technical Manager, Bekaert BP Underground Solutions
Achieving decarbonisation in tunnel construction is not only possible but crucial from a sustainable perspective. Currently, nearly 70% of embodied carbon in tunnels
is attributed to concrete linings. To bring this down, we need to better consider the sprayed concrete lining as part of the permanent lining. The excessive structural design using cast-in-place
(CIP) concrete or other lining structures, used in the current practice, have a significant impact on cost, excavated volume of rock mass, construction time and also CO2
emissions. Changing the combination of temporary sprayed
concrete liner and permanent CIP liner to, instead, only a permanent shotcrete liner and having improved mix design could reduce CO2
emissions from the materials
production and lining construction by 75%. Historically, tunnels constructed using sprayed
concrete have been based on: 1 Temporary sprayed concrete lining is placed to stabilise the opening after excavation and to contain short to medium-term loads;
2 A waterproof membrane is then placed upon the temporary lining (once that initial lining is fully stabilised), and therefore will be located between this layer and the secondary, permanent linings yet to be placed; and,
3 A permanent CIP concrete lining is installed to contain long-term loads and provide durability and watertightness.
Over the last 30 years, modern sprayed concrete technology and quality has evolved and now equips the tunnelling industry with a more economical tunnel lining system as a Permanent Sprayed Concrete Lining (PSCL), which replaces the CIP final lining. This is also known as the Single Shell Method. The use of high-performance steel fibres in the
sprayed concrete eliminates the traditional steel bar reinforcement in the final lining, providing a reduction in the total quantity of reinforcing steel required, a reduction in lining thickness and also in the quantity of concrete required. Also, with less labour being required plus savings
in both construction time and cost, this new method provides a more durable and sustainable structure while reducing the carbon footprint of the project. Note, the term ‘single shell’ does not refer to the
placing of a single sprayed concrete layer but to the interaction of several layers as a single shell (initial support), rock bolts (if needed), water proofing membrane (if needed), and the shotcrete final layer. The possibility of using permanent sprayed concrete
allows this preliminary lining to be considered for carrying the permanent load. In this case, the possible solutions are to consider: 1 the preliminary sprayed, fibre reinforce concrete (FRC) lining collaborating with the final lining;
2 the preliminary sprayed FRC collaborating with a further sprayed lining in a second stage; or
3 only the preliminary FRC lining as the final stage. Above: EN 14 488-3 Method B IMAGES COURTESY OF BEKAERT
The use of sprayed concrete to ensure the double functions of temporary support and final lining is a relevant approach to the eco-design of underground structures. This approach can minimise the thickness
September 2025 | 35
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