Conditions of the cavity formation and sinkholes in the practical ground

Abstract

Sinkhole accidents bring various damages to the society and the infrastructures. Some of the accidents are induced by internal erosion with the seepages. Concretely, soil is drained to cracks and breakages of sewer pipes in urban areas with rainfalls. The underground cavities are expanded by soil drainages and finally it causes sinkholes. Recent studies simulated these phenomena but there are some differences between experimental conditions and actual ones. For examples, practical ground containing fines is not uniform, having lower permeability than of the model ground. This study aims to make connection of the knowledges indicated by the previous researches using simulations by the model ground, and actual phenomena happening in the ground. Firstly, we performed the model tests using a backfill soil. Obvious collapse and cavity expansion hardly occurred because of the very low permeability. It is suggested that two specific conditions are required to promote the cavity expansion; one is the strong seepage close to the cavity, and which directly flow into there. Another is repetitions of drying-wetting in the ground. After the end of infiltration, cone penetration test was performed to evaluate the stiffness vicinity of the cavities. We proposed the new evaluation method based on the fines contents.