Evaluation of defective sewer pipe-induced internal erosion and associated ground deformation using laboratory model test

Sinkholes induced by long-term internal erosion around defective sewer pipes have been widely reported. There is a need for an efficient method to understand the influence of pipe defects on internal erosion and ground settlement. This paper presents an approach to the investigation of erosion-induced ground settlement and the susceptibility of pipe bedding materials to internal erosion. A new and efficient erosion test apparatus is introduced, aided by controlling most of the key influencing parameters. The corresponding ground displacement is tracked by image correlation based on particle image velocimetry (PIV). The basic parameters investigated are (i) the process of cavity initiation and evolution, (ii) the rate of soil loss, (iii) the gradation of eroded soil, and (iv) the corresponding ground displacement. The results indicate that particles less than 0.3 mm are highly vulnerable to erosion through 5 mm openings of embedment material with a maximum particle size of 4.75 mm. The proposed method is beneficial, as it allows measurement of the deformation at any time and at any location throughout the test and facilitates checking the resistance to erosion of pipe embedment materials.