A non-Darcy flow CFD–DEM method for simulating ground collapse induced by leakage through underground pipeline defect

Ground collapse due to soil erosion near pipeline defects involves soil loss and orifice outflow, which may lead to non-Darcy flow, but it is often ignored in numerical simulations. In this study, a computational-fluid-dynamics and discrete-element-method (CFD–DEM) coupling method is developed considering the non-Darcy flow. In contrast to the Darcy Equation, which tends to overestimate fluid velocity and drag force at high Reynolds numbers, the newly developed CFD-DEM method has been validated and found to be applicable across a wide range of Reynolds numbers. Utilizing the capabilities of this method, the investigation of ground collapse mechanism is conducted. Results show that the trajectories of lost particles approximately form a straight line from their initial positions towards the defect, with higher velocities for particles closer to the defect. It is likely the main reason that the evolution of particle loss closely resembles a progressive contraction of an ellipse, while the evolution of the loosening zone resembles an upward movement and expansion of an ellipse. The soil settlement is uneven both in the horizontal and vertical direction. As the particle loss increases, the shape of the surface settlement curve transitions from a normal distribution to a logarithmic function.