Catastrophic transition from suffusion to leakage: Micromechanical insights and a generalized criterion equation

Current analytical frameworks fundamentally decouple suffusion from leakage, leaving a critical theoretical gap in quantifying the transitional tipping point (i.e., suffusion catastrophe). To bridge this gap, this study leverages a robust CFD-DEM framework to conduct representative volume element (RVE)-based erosion simulations. By employing upscaling theory, the macroscopic criterion equation for suffusion catastrophe rigorously is derived. The spatial–temporal evolution characteristics, physical essence, fundamental cause, and key geometric factor of suffusion catastrophe are first revealed. Based on this, the concept of catastrophe resistance F rc is introduced to establish the catastrophe mechanical model. It is found that the catastrophe resistance F rc of soil is essentially proportional to its normal stress F n . Subsequently, the ratio between the two, denoted as the catastrophe resistance coefficient μ c , is found to exhibit a logarithmic decay with the outlet span ratio R o/c . Accordingly, the expression for the catastrophe resistance F rc and the catastrophe criterion equation are established. This establishes a crucial cornerstone for field-scale, multi-physical modelling of seepage-induced erosion. It thereby facilitates robust early warning systems for severe geohazards, including massive water-soil inrush, substantial strata subsidence, and catastrophic structural failure.