IMMERSED TUBE TUNNELS | TRANSPORT


The Hong Kong-Zhuhai- Macao Bridge Link comprises a 6.7km-long immersed tube tunnel connecting two artificial islands. Trelleborg supplied sealing systems designed to accommodate significant movement tolerances while maintaining long-term watertight performance in a complex marine environment.


These include dynamic compression testing on full-scale seal specimens to simulate seismic loading, extended- duration testing to capture time-dependent effects such as relaxation and surface ageing, and watertightness protocols that replicate real-world external pressure conditions. This means that rigorous validation requires conditions that reflect operational reality, rather than simplified laboratory environments. The Rotterdam Metro tunnel demonstrated what this


evidence base can reveal. Seal samples retrieved after more than 60 years in service showed limited to no ageing in the material core, with surface changes present but within parameters consistent with significant remaining service life. Real-world observation also drives advanced requirements in ways that design standards alone cannot anticipate. Inspection programmes on older tunnels have identified that corrosion at the interface between wet and dry zones within a joint can accelerate surface degradation beyond standard model predictions. It is this kind of operational insight, systematically captured and fed back into industry standards that will define how the sector meets the demands of the next generation of infrastructure.


CASE FOR PROACTIVE MAINTENANCE Unplanned tunnel maintenance is expensive, disruptive and has the potential to compromise lifetime expectancy of an asset. The traditional model of “inspect when concerned, repair when necessary”, is increasingly difficult to justify from either commercial or safety perspectives. Preventative programmes allow owners to plan


interventions strategically, minimise operational disruption, and extract maximum value from their infrastructure assets. As many immersed tube tunnel assets are partway through their life cycle, identifying where components can be upgraded and proactively maintained is vital for ensuring optimal asset performance. In many cases, relatively minor, well-timed upgrades can extend a tunnel’s service life significantly. This shifts the question from whether a tunnel needs repair to what investment today will deliver benefits over the next few decades. This evolution is redefining what partners in this space


are expected to offer. Beyond supplying sealing systems, value increasingly lies in the ability to inspect joints,


interpret performance data, identify emerging risks, and advise on prioritised interventions across the tunnel life cycle. Diagnostic capabilities that span inspection, monitoring, and performance assessment are becoming as critical as execution in new-build projects, which enables owners to move from reactive response to informed, long-term asset stewardship.


SUSTAINABILITY:


A PERFORMANCE DIMENSION Environmental accountability has moved from a reputational consideration to a contractual requirement. The Greenhouse Gas Protocol is a globally recognised standard for categorising and recording emissions, with varying interpretation and requirements across regions. For example, in European markets, large companies are required to report their Scope 2 and Scope 3 carbon emissions. This has implications for tunnel owners as they are increasingly required to account for emissions across their supply chains — from the extraction and manufacture of steel, concrete, and rubber elements to the long-term operational energy profile of the completed asset. Material traceability, Environmental Product


Declarations for tunnel components, and circular end- of-life planning are also entering the mainstream of specification requirements. This adds a dimension to resilience thinking that goes


beyond structural and operational performance. A tunnel built to last at least 120 years that requires high-carbon maintenance interventions, or whose components carry no credible environmental provenance, does not meet the sustainability obligations that asset owners are now contractually bound to report against. The most resilient immersed tunnel infrastructure of the next generation will integrate structural durability, operational performance and environmental accountability as a single engineering challenge rather than treating them as separate concerns. The immersed tube tunnel industry is better equipped


to face the challenges of extended design lives, more demanding operating environments, and higher sustainability standards than at any previous point in its history. Decades of operational evidence from installed infrastructure provides a foundation that few construction disciplines can claim in the same way.


July 2026 | 19


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