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A new shield for Kansai International Airport
In July 2026, construction crews began a monumental task on the artificial island that hosts Kansai International Airport: erecting a 9,500-metre underground wall. Part of the airport's second-phase expansion, which also includes a new runway, terminal, and island, the wall's primary goal is to raise the runway and stabilize the island's groundwater, safeguarding the airport against the twin threats of sea-level rise and typhoon-induced flooding.
Why an underground wall?
Because Kansai Airport sits on reclaimed land, its foundations are vulnerable to changes in water pressure. Over the years the island has experienced gradual subsidence, and surrounding seawater can seep into the ground, raising the water table. An underground wall that blocks seawater from entering the island's interior prevents this seepage, keeping the ground stable and the runway level.
The scale of the project
The wall stretches 9,500 metres, essentially encircling the island's perimeter, and is built beneath the surface so it does not interfere with current operations. Construction involves excavating a trench, laying a waterproof membrane, and pouring high-strength concrete. The wall's height is designed to match the projected rise in sea level over the coming decades, providing a long-term safety margin.
Engineering challenges
- •Sand, clay, marine sediments
- •Ground stabilization: grouting and soil nailing
- •Reinforce trench walls before concrete
- •Several metres of water depth
- •Additives improve impermeability
- •Greater durability
Building a wall this long on a reclaimed island presents technical hurdles. First, the soil is a mix of sand, clay, and marine sediments that can be unstable when disturbed; engineers use ground-stabilization techniques such as grouting and soil nailing to reinforce the trench walls before concrete placement. Second, the wall must resist the hydrostatic pressure of seawater, which can reach several metres of water depth, so the concrete mix includes additives that improve impermeability and durability.
Environmental safeguards
The project incorporates a suite of environmental measures. A monitoring system tracks groundwater levels in real time, letting operators adjust pumping rates and prevent over-extraction. The construction schedule is coordinated with marine traffic to minimize disruption to shipping lanes around the island, and noise- and dust-control protocols protect nearby residents and wildlife.
Impact on airport operations
- •Flights handled without interruption
- •Runway and taxiway unaffected
- •Wall is underground
- •Phased schedule
- •Maintenance with minimal impact
While the wall is being built, Kansai Airport continues to handle flights without interruption. Because the wall is underground, runway and taxiway activities remain unaffected. The project is phased so that any necessary maintenance or repairs can be carried out with minimal impact on flight schedules.
Long-term benefits and what's next
Once completed, the wall will provide a robust barrier against future sea-level rise, projected to increase by up to 0.5 metres over the next 50 years. By raising the runway and stabilizing the island's foundation, the airport will maintain its operational integrity and safety standards for decades, signalling a broader commitment to climate resilience in Japan's critical infrastructure. The wall is only the first step of the second-phase expansion: subsequent phases will add a new 5,000-metre runway, a modern terminal, and additional support facilities, positioning the airport to meet growing passenger demand while staying resilient to climate change.
Summary
Kansai Airport's 9,500 m underground wall, begun in July 2026, blocks seawater seepage to stabilize the reclaimed island's groundwater and keep the runway level, all without interrupting flights. Designed for up to 0.5 m of sea-level rise over 50 years, it is the first step of a second-phase expansion that will include a new 5,000 m runway and terminal.