Rainfall- and leakage-induced soil erosion and debonding–migration effects

Leakage from buried drainage pipes can cause underground road damage and eventually lead to the formation of cavities. Additionally, rainfall increases the probability of collapse disasters. However, the processes by which rainfall and pipeline leakage lead to water infiltration and subsequent migration of underground soil—thereby forming cavities—are not well understood. To address this challenge, we developed a physical model to simulate the soil erosion and migration process. This model, which incorporated both model testing and theoretical analysis, simultaneously simulated the effects of rainfall and pipeline leakage on soil erosion and migration. In addition, particle-level optical tracing microscopy was used to investigate the mechanisms of rainfall- and leakage-induced debonding and migration of soil particles and to analyze the characteristics of soil migration and critical gushing. Results revealed that pipeline-leakage-induced soil erosion weakened the bonds between soil particles surrounding the pipes and caused the initial opening of cracks between particles, the fluid began to diffuse from these initial openings, forming ice-flower-like patterns around the point. Under leakage conditions, the microchannels of runoff were interconnected, and the migration of eroded soil exhibited a gridded distribution of soil agglomerates. Moreover, a critical velocity of erosion migration occurred, once this threshold was exceeded, the dispersal of water and soil medium led to the instability of the soil structure. Rainfall and leakage intensified the formation of runoff channels and expanded the cross-sectional areas of these channels. The merging of infiltrated rainwater and leakage flow initiated the gushing of pipe-flow soil. The critical time of gushing in the test environment was approximately 46% earlier than that in the same period of the only-leakage condition. The average area of pits formed by soil collapse was also increased by approximately 105%. Furthermore, the soil erosion and migration process comprised three stages: debonding, migration, and gushing. Rainfall infiltration and leakage-induced erosion synergistically formed soil cavities, intensifying underground soil loss. The soil cavities expanded upward, causing the ground surface to collapse. An "e"-shaped vortex halo formed around the pit created by the collapse of the ground surface, leading to secondary collapses. The findings of this study provide a scientific foundation for the prevention and control of road collapse.