2
6
In preparation for the opening of Expo 2025, Osaka, Kansai, Japan (hereinafter referred to as “the Expo”) water was let into the Water Plaza and Sea of Connections starting in mid-February. Following the introduction of water, erosion was observed on the sea walls of both areas. The introduced water is believed to be the cause of this erosion. Measures will be implemented to ensure the opening of the Expo is not impacted.
Current Status of Erosion (as of 7:00 on 7 March)
● Of the 500 meters of the Water Plaza seawall, erosion has occurred on a stretch of about 120 meters on the east side. No erosion has been observed from the center to the west.
● Of the 600 meters of the Sea of Connections seawall, erosion has occurred on a stretch of about 480 meters from the west. No erosion has been observed from the east side.
Possible Causes of Erosion
● Waves caused by wind after water was introduced into the Water Plaza and Sea of Connections are believed to have eroded the embankment slope along the revetment edge.
● Strong westerly winds at the Expo site caused waves to travel from west to east, leading to erosion. No erosion was observed on the west side of the Water Plaza, which is shielded from the waves.
● Additionally, water was introduced into the Water Plaza in preparation for the water show, before water was introduced into the Sea of Connections. This resulted in a larger difference in water levels than planned which caused water to flow from the Water Plaza into the Sea of Connections, exacerbating the erosion.
Safety of the Grand Ring and Perimeter Road along the Water Plaza
● Beneath the Grand Ring, there is a ground improvement layer about 1.5 meters below the embankment (approximately 2 meters high). The foundation structure is a pile foundation supported by solid soil at a depth of around 60 meters. The Grand Ring is supported by foundation beams that connect the pile foundation, ensuring that the structure remains unaffected by erosion and remains stable.
● The perimeter road along the Water Plaza (used by electric buses and freight vehicles) is paved with asphalt over a reinforced concrete floor slab, which is integrated with the foundation beams. Since the road is part of the Grand Ring foundation, it is also stable.
● We have consulted with academic experts to ensure the safety of the Grand Ring and have confirmed that the perimeter road is not compromised by erosion of the revetment.
Future Measures
We are evaluating options to protect the eroded revetment, such as covering it with crushed stones. Measures will be implemented to ensure these issues do not affect the opening of the Expo.
Seawall Erosion Location
*DL (Datum Level): The basic water level for port construction established by the Osaka Port Bureau
*Current Status of Erosion at the Water Plaza and Sea of Connections
Photo 1: Wide view and zoomed in view of the Water Plaza side (Date taken: 7 March 2025)
Photo 2: Wide view of the Sea of Connections side (Date taken: 7 March 2025)
Photo 3: Zoomed-in view of the Sea of Connections side (Date taken: 7 March 2025)
To see French version, click here.