Experimental Study on Cavity Formation and Collapse in Fine-Grained Soils Triggered by Sewer Damage
Experimental Study on Cavity Formation and Collapse in Fine-Grained Soils Triggered by Sewer Damage
In January 2025, a tragic road collapse occurred in Yashio City, Saitama Prefecture, caused by soil outflow due to damaged sewer infrastructure. Such incidents, often associated with aging structures, pose serious risks to urban safety. Ground subsidence generally begins with the formation of an underground cavity that propagates upward, eventually leading to collapse when the loosened zone reaches the ground surface. Therefore, understanding the initiation and expansion of cavities is essential for effective prevention.
Previous studies have mainly examined collapse behavior in sandy soils through model experiments, whereas research on fine-grained soils remains limited. The soil at the Yashio site was characterized by a high fine particle content. In sandy ground, collapse hazards can be evaluated based on cavity width and overburden thickness.
To clarify the mechanism behind the Yashio event, model experiments simulating cavity formation and ground subsidence were conducted using soil with a high fine particle content. Soil outflow was triggered through a slit representing sewer pipe damage, and the processes of cavity initiation, expansion, and collapse were observed. The results indicate that collapse behavior in fine-grained soil differs from that in sandy soil, and hazard assessment cannot rely solely on cavity width and overburden thickness. These findings contribute to improving infrastructure maintenance and disaster prevention strategies.
Ayaka Sugawa; Reiko Kuwano
11th International Conference on Physical Modelling in Geotechnics (ICPMG2026)
Session 3: Resilient geotechnical infrastructure
https://doi.org/10.53243/ICPMG2026-233