Dealing With Existing Foundation Piles: Challenges of Urban Redevelopment in Densely Built Japanese Cities With Implications for Earthquake Response

ABSTRACT In recent years, Japan's major cities have undergone vigorous redevelopment, leading to the demolition of many existing buildings. A major challenge in this process is how to deal with the existing foundation piles, specifically, how to execute the removal of these piles and the subsequent backfilling. This Short Communication reports on the current situation in Japan. It first outlines the ongoing redevelopment efforts and provides an overview of common methods adopted for pile removal in Japan. It then presents a case study of actual pile removal and backfilling work, showing that the stiffness of the surrounding ground after backfilling, particularly within about 2 m of the removal location, tends to decrease to about 60%–80% of the original ground's stiffness. It further suggests that staged‐construction analysis with advanced numerical codes has the potential to reasonably simulate the pile removal process. Finally, the article highlights future technical challenges, including how to account for the reduced stiffness near the backfilled zone and how to control the properties of the backfill material, particularly with respect to their influence on the horizontal resistance of piles during earthquakes. It also discusses how pile removal and backfilling methods can adapt to emerging concepts such as carbon neutrality and the circular economy. Specifically, it touches on the reuse of existing piles in new buildings and the option of leaving old piles in place rather than removing them.