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Courtesy of Hiroshima Electric Railway Co.’s Hiroshima Station joint venture construction office Workers place polystyrene blocks between concrete retaining walls in Minami Ward, Hiroshima.
The Yomiuri Shimbun
7:00 JST, February 19, 2025
HIROSHIMA — For the first time in Japan, lightweight polystyrene blocks have been used to build the foundations for the main line of a commercial railway.
The blocks were used instead of soil and sand for an elevated section of Hiroshima Electric Railway Co.’s Ekimae Ohashi route, under construction in Minami Ward, Hiroshima. The new line will link to the new Hiroshima Station building scheduled to open in March.
The blocks allow for reduced weight on a section that runs directly over an underground event space. This 72-meter section of the about 260-meter elevated track extends from the Enko River’s left bank to Ozu-dori avenue. Using conventional construction methods for this section would have necessitated huge pillars running through the event space, which would have impacted the function of the space for gatherings. The soil to elevate the tracks would also have placed a heavy load on the area beneath.
To get around these problems, the firm decided to build the foundations using expanded polystyrene construction, in which lightweight polystyrene blocks are placed between concrete retaining walls. About 2,000 of the blocks, which measure about 2 meters by 1 meter by 50 centimeters, have been laid edge to edge to fill an area about 55 meters long, 5 meters high and 6.6 meters across, with some of the blocks having been cut when necessary. This construction method is commonly used on roadways.
Made specially for construction projects, the blocks are denser and harder than regular polystyrene. They are resistant to deformation and will not collapse even when stacked on top of each other. Metal fittings hold the blocks in place, and there are three layers of the blocks, with a sheet of concrete capping each layer. A single block weighs 25 kilograms, or 1.4% of the weight of a similar volume of soil. This allows for significantly lighter foundations. The blocks also are being used in the tram stop inside the station building.
Work to install the blocks has already been completed, and preparations have begun for laying the tracks. Trams are scheduled to begin rolling in and out of the new station building sometime this summer.
“The polystyrene blocks are strong enough for this project, and the retaining walls are able to withstand huge earthquakes,” said Osamu Hirai, deputy head of Hiroshima Electric Railway’s Hiroshima Station joint venture construction office. “Although this method hasn’t been used much in construction projects in major cities, we want to move forward with this work safely.”
