Experimental Study of Erosion of Defective Pipeline under Variable Water Level

Summary Driven by groundwater, defective pipelines can cause soil erosion and pose significant risks to the surrounding infrastructure. In this study, the evolution and collapse characteristics of formation stress caused by defective pipelines were considered not only under the constant groundwater level condition that previous studies have focused on but also under rainfall or flood scenarios (the groundwater level rises briefly and then quickly returns to its original height). This study developed a large-scale 3×2×2 m 3D physical model experimental setup to simulate the process of seepage erosion and collapse within the strata induced by groundwater. The results showed that groundwater seepage provided power for the migration of soil in the stratum, and the defects of pipelines offered migration space for the soil. When soil migration induced by groundwater into the defective pipeline caused the overlying strata to lose bearing capacity, surface subsidence occurred. Compared with the condition of constant groundwater level, the collapse volume under variable groundwater level decreased by 3.48%, but more irregular sinkholes appeared on the surface, which posed a greater threat to regional infrastructure and human activities. The increase in the height of the constant groundwater level not only prolonged the erosion process but also induced a larger erosion cavity and expanded the collapse volume. The increase in overburden thickness intensified the stress change in the stratum, resulting in a larger reduction in in-situ stress and enlarging the scale of erosion and collapse. This study uncovers the critical mechanisms by which rainfall and flooding trigger surface collapse around defective pipelines, offering valuable insights for pipeline design, maintenance, and risk assessment in the petroleum industry.