Evaluating lining alternatives to ensure sustainable underground infrastructure

Montreal’s Metro Blue Line Extension consists of nearly 6km (4mi) of TBM tunnel and five new stations. The owner and its team are committed to integrating sustainability best practices on the project, strategically evaluating the extension’s design to reduce emissions and optimize solutions. The results of the study extend beyond Montreal to further benefit the wider tunneling industry.

The challenge

AECOM used the Envision framework, a system of criteria and performance objectives, to evaluate the lining design.

For SEM excavation, the baseline design comprised a layer of temporary shotcrete, a cast-in-place (CIP) lining and an invert using ordinary Portland cement. The alternative used low carbon concrete and replaced the temporary shotcrete and CIP arc with steel fiber-reinforced shotcrete using Dramix® 3D 65/35BG, also known as a permanent sprayed concrete lining.

For TBM segments, the baseline design used ordinary Portland cement reinforced with rebar, while the alternative used low carbon concrete and replaced the rebar with Dramix® 4D 80/60BGP fibers.

The solution

The Envision framework revealed huge potential for CO2 emissions reductions.

The alternative, low-carbon permanent sprayed concrete lining design for SEM excavation offered a total CO2 emission savings of 79%. And the alternative design for the TBM segments nearly halved the CO2 emissions, from 6.7 tons per meter of tunnel to 3.6 tons.

Based on these results, a permanent sprayed concrete lining was chosen as the optimum sustainable solution for the Metro Blue Line Extension project in sections of tunnel using SEM excavation.

Steel fiber-reinforced precast concrete segments made with low-carbon concrete will be used in sections mined by TBM.

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Evaluating lining alternatives to ensure sustainable underground infrastructure

The challenge

The solution

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