Hanshin Expressway Large-scale Renewal Project
No. 15 Sakai Line, vicinity of Minatomachi
~opened in 1972~

Complicated Structures Lying on Top of Each Other in a Limited Urban Space

Major causes and damage

The steel foundation employed to lighten the structure because of complicated layers of structures, including an underground mall and a railroad track, under the foundation is rapidly being corroded by the rising groundwater level.

Causes and Condition of Damage

Changes in the surrounding environment after the completion of the expressway raised the groundwater level.
Consequently groundwater flowed into the internal void of the steel foundation, which promotes corrosion.
The internal space is constantly kept at high temperatures with the water level continuously rising and lowering.
The steel foundation is still in an environment that further promotes corrosion.

Back in the Days of Construction

Construction site in those days

Even before construction of the expressway, this section, which crosses the busy street of Minami, the center of Osaka, was characterized by a web of underground layers composed of railroad stations and a shopping mall.
It was impossible to drive piles just over the underground shopping mall to construct a bridge.
Therefore, some idea had to be put to action to minimize the load on the underground structure.
This is why a special light-weight pile-free steel foundation was adopted.