Questions emerge about the rubber material sealing underwater tunnels
Engineers have raised concerns about how long rubber seals in undersea tunnels will last, after new research pointed to serious durability problems. The study, published in the journal Tunnelling and Underground Space Technology on 28 March 2026, focuses attention on the GINA gasket, a key seal used in these submerged joints. Led by researchers from Shijiazhuang Tiedao University (STDU) in China, the work used samples taken from the Yuliangzhou tunnel and tested them under real-world pressure and environmental conditions. The rubber showed a large drop in its sealing force, which could change expectations about how long these structures will hold up.
A big drop in sealing force
Rubber seals in undersea tunnels are generally expected to keep things watertight for up to a century. But this report found a dramatic 67.66% loss in sealing force when the rubber was subjected to both compression and saltwater, conditions that mimic what happens in service rather than in neat lab tests.
The finding indicates a hidden loss of sealing pressure rather than visible wear. Engineers who had relied on a century-long performance for these seals will need to rethink those assumptions.
The GINA gasket is squeezed between steel faces at tunnel joints to create the contact stress that stops leaks. Earlier testing had already shown the bottom edge of the gasket as a weak spot, prone to starting leaks when pressure falls, especially if the tunnel moves. If the joint opening grows beyond 47 mm, waterproofing can fail. Rotation of the joint adds risk too, because it can misalign the seal and reduce edge pressure.
How the rubber ages
To measure how the seals change over time, the team ran accelerated ageing tests. Over 90 days they recorded notable changes in the GINA gasket’s material: hardness rose by 14.18%, density went up by 5.88%, and the glass-transition temperature shifted by about 3.2 °C.
The degradation followed three stages: a rapid early fall in force, a more moderate middle decline, and a slower final taper. Saltwater and oxygen attacked the rubber from the outside in, breaking long molecular chains into shorter, weaker ones. That chemical wear roughened the surface and reduced the rubber’s flexibility, so the most resilient parts on day one became less elastic over time.
Looking ahead: what to expect and what to do
Projecting performance out to a century suggests contact pressure could fall to 1.51 MPa (about 219 psi). Even with that drop, the pressure would still be above the waterproofing threshold of 0.61 MPa (approximately 88 psi), so there would be some margin, though it is tighter than previously thought. Previous studies that only looked at seawater effects had predicted a decline to 2.32 MPa (roughly 336 psi), so this new work indicates a larger reduction.
Based on the findings, the researchers recommend changes for tunnel designers:
- tweak rubber compound formulations,
- revisit compression targets,
- overhaul inspection schemes.
They also urge empirical testing that mirrors real operational conditions rather than relying on isolated lab tests, which should give more realistic guidance for keeping tunnels watertight.
The study provides data on how the GINA gasket behaves and recommends closer monitoring of contact stress within seals, especially at the lower edges of joints where structural and environmental pressures meet.
The authors recommend that tunnel operators convert these projections into maintenance timetables and proactive interventions. They also advise that policymakers, engineers and stakeholders reassess current norms and prepare preventive measures to safeguard the structural integrity of undersea infrastructure.