Study on the loosening mechanism of the ground due to aging of sewerage pipes and its countermeasure methods

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It has been reported that the roadway surface locally subsides due to settlement in a base course. In most cases, a sewerage pipe exists underneath the subsidence part. In order to understand significant factor on local subsidence at road surface, model test was performed to generate a cavity in the model ground. Water was supplied into each model ground by Toyoura sand from the defect part with a same hydraulic head and soil was drained from the same defect part, which is created on the bottom of model ground. An industrial X-ray computed tomography (CT) scanner was used to scan the condition in the model ground at each step of water supply-drainage cycles ; the cavity generation in the model ground was observed 3-dimensionally. The analysis of CT image evaluated the range of loosening area, visually and quantitatively.