Technical challenges and innovations in existing pile extraction and associated borehole backfilling in Japan

This paper critically evaluates and proposes innovative approaches to address the technical challenges associated with extracting existing piles and backfilling the associated boreholes, specifically in the context of Japan. Japan's rapid post-war economic growth has resulted in an infrastructure that is now aging, necessitating the demolition and subsequent reuse of structures. The prevalent use of pile foundations in soft soil conditions in Japan presents unique challenges following demolition, including differential settlement and complications for future construction on the same site. Current practices in Japan for pile removal are outdated and rely heavily on field experience without the support of standardized guidelines, leading to unresolved issues in improving the removal process. This paper provides an in-depth review of the status of technological advances in pile extraction and removal, as well as the development of backfill materials, with a focus on Japan's unique geological, demographic, and urban development factors. It highlights the risks associated with the traditional wire rope method and presents an innovative pile tip gripping and lifting method that aims to improve safety and efficiency by minimizing friction and preventing accidents. It also discusses the critical role of backfill treatment in preventing subsidence and outlines the performance requirements for fill materials, emphasizing the need for materials that provide uniform strength, prevent material segregation, and resist groundwater infiltration. Specifically, the paper discusses the development of cement-based fillers for borehole backfilling in Japan and demonstrates the effectiveness of sodium carbonate and thickeners in improving the physical and rheological properties of cement slurries. Finally, the paper emphasizes the urgent need for innovative technologies and methodologies for pile extraction, removal, and borehole backfilling in the Japanese context, highlighting their importance in ensuring safe, sustainable, and efficient land use in urban areas while addressing environmental concerns and stakeholder interests in land transactions and construction projects.