Visualization of Three Dimensional Failure in Sand Due to Water Inflow and Soil Drainage from Defective Underground Pipe Using X-ray CT

Abstract

The roadway surface locally subsides due to material aging or settlement of a base course in particular, resulting in failure of the ground with a plenty of water inflow. In most cases of roadway subsidence, underground pipes exist underneath the subsidence. In order to understand significant factors leading to local subsidence at a ground surface, a series of model tests using sandy soil were performed with the concerned defect configuration of the underground pipe and hydraulic condition. An industrial X-ray computed tomography (CT) scanner was used to investigate the behaviour of the model ground at each step of monotonic water inflow, monotonic soil drainage and the cyclic water inflow—soil drainage. Then, the behaviour density change of the model ground was visualized as a density change in two-dimensions and three-dimension. This paper concludes that the cyclic condition of water inflow—soil drainage caused fatal ground failure as the water inflow process created a water path disturbing the soil. Subsequently, the soil drained and the soil particles were interlocked due to the drainage. The movement of soil particles were restricted with the arching effect; and, the factors causing the cavity in the ground were not only the existing defect in the underground pipe but also the water flow towards the defective part after the loss of capillary force.