Experimental study on the soil erosion through a defective pipe under the cyclic infiltration-exfiltration flow

Abstract

Ground collapse is becoming a global issue, and it is of significant importance to understand its mechanism and develop models for the prevention and mitigation of this hazard. The cyclic infiltration and exfiltration through defective pipes can lead to soil loss, resulting in ground collapse or sinkholes. This study conducted physical model tests to examine soil erosion through a defective pipe under cyclic infiltration-exfiltration flow, using simplified gap-graded soils made up of bimodal particles composed of two different diameters of glass spheres. Three types of erosion behaviors were identified: clogging, incomplete erosion, and complete erosion. Fines loss can significantly contribute to ground subsidence for bimodal soils, particularly for those with a particle size ratio greater than 2. After introducing a non-dimensional parameter that accounts for particle size, defect size, and fines content, a phase diagram was developed to determine erosion behavior based on the cycle number. When the non-dimensional parameter exceeds 1.75, erosion characteristics may change to complete erosion after applying seven cycles of infiltration and exfiltration. Finally, an analytical model was proposed to predict soil mass loss considering the cyclic number of the exfiltration and infiltration flow for the incomplete erosion.