Coupled CFD–DEM analysis of soil cavity formation and gas diffusion during buried pipeline leakage

Abstract After the leakage of a buried pipeline, the overlying soil structure deforms under the high-speed impact of escaping gas, influencing both leakage and diffusion behaviours. This deformation typically appears as a soil cavity above the leakage port, especially in medium- and low-pressure conditions. In this study, the formation process of soil cavities is investigated using CFD–DEM coupled numerical simulations. The control variable method is applied to examine how different conditions affect cavity size and gas diffusion, and the sensitivity between cavity characteristics and leakage behaviour is analysed. Results show that the leaked gas forms a high-velocity zone near the leakage port, generating negative pressure in the surrounding area. Soil cavities generally form and stabilize within 0.1 s under gas impact. Soil particle size and porosity significantly influence the cavity formation time by altering the pore structure and total pore volume. The average sensitivity coefficients of the maximum cavity width to gas leakage velocity and the highest dangerous range (HDR) are 5.71 and 18.78, respectively, indicating that larger cavity widths correspond to higher leakage velocities and greater HDR. Therefore, the maximum cavity width serves as the most appropriate indicator for evaluating soil cavities caused by buried gas pipeline leakage.