Embodied carbon is the amount of carbon emitted during the lifetime of an infrastructure project, from manufacturing, transportation, and construction to its end of life. There has been a new focus on these carbon emissions because they will likely account for a large portion of our remaining carbon budget. Microtunneling is a trenchless tunneling technique used to bore relatively small utility tunnels, which are ideal in urban areas where there is a need to limit surface disruption, rather than the usual open-cut process used for utility work.

In performing a literature review the authors of a new paper in the Journal of Geotechnical and Geoenvironmental Engineering identified a knowledge gap. There is a wealth of research on the lifecycle of infrastructure, but when narrowing in on infrastructure projects with underground components (e.g., railways) and their conclusions on EC, there was an obvious gap in presenting calculations for tunneled sections, particularly related to pipe manufacturing. 

In “Embodied Carbon Analysis of Microtunneling Using Recent Case Histories,” researchers Alexander W. Swallow and Brian B. Sheil sought to identify this shortfall and improve understanding of carbon emissions related to MT. They outlined five objectives: 1) develop a methodology with boundaries to better calculate the EC of MT, 2) clearly define the EC for various project elements, 3) create a custom database of MT using recent project histories, 4) identify carbon-intensive construction processes and stages, and 5) assess design optimization impacts. Applying their methodology on three case studies their findings suggest that EC of MT is lower than comparable projects using traditional open-cut techniques. Learn more about their research at https://doi.org/10.1061/JGGEFK.GTENG-10989. The abstract is below.


With increasing demand for sustainable underground infrastructure and pressure to reduce embodied carbon (EC), microtunneling (MT) has become an increasingly popular trenchless method of installing buried utility tunnels. Life-cycle analyses have shown that trenchless methods cause lower emissions than traditional open-cut construction. However, existing literature specifically considering MT is limited and fails to consider the impact of the entire construction process. In this paper, an approach for calculating the EC of MT is presented. The proposed approach is applied to three recent case histories in the United Kingdom through the development of a bespoke MT EC database in collaboration with industry partners. Total emissions across all three projects (870 m of pipeline) total 1,005 tCO2e. Production of materials and components is shown to account for an average of 68.5% of EC across the three projects, with most of these emissions coming from the key structural materials, namely concrete and steel. Sensitivity analyses demonstrate that the source and production method of steel products have a significant impact on EC. Site activities also make a significant contribution, accounting for an average of 20.5% of total EC. Normalization of the results suggests that MT produces less EC than open-cut pipeline installation and highlighted how increasing drive lengths and reducing the number of shafts can significantly reduce EC. One of the case studies is then used as an example to quantify how the reduction of intermediate launch/reception shafts can reduce overall EC.

Explore how you can leverage this research in the ASCE Library: https://doi.org/10.1061/JGGEFK.GTENG-10989.