Numerical investigation of internal erosion mechanisms regarding stratigraphy: Agly dike case study

Abstract

Internal erosion poses a significant threat to the safety of the water-retaining structures. Due to its subterranean nature, the process of internal erosion is difficult to observe directly and evaluate properly, even when typical erosion signatures are captured at the surface. Therefore, predicting internal erosion or elucidating the underlying mechanisms of superficial erosion indicators remain considerable challenges in geotechnical engineering. In this study, a numerical investigation was conducted to explore the mechanism responsible for the numerous erosion signatures (sinkholes, sand-boils, and leaks) observed at the Agly dike, in France, through a cooperated geophysical-numerical approach. Simulated configurations were mapped according to the actual stratigraphic structures identified by geophysical results (EMI and ERT). A multispecies transport finite element method was employed to examine the seepage and suffusion dynamics under periodic flooding conditions. Systematic comparative analysis demonstrated that the unique stratigraphic structures and geometries played a governing role in the occurrence of erosion signatures in situ. Specifically, the paleo-channel throat promotes sinkhole formation via suffusion and contact erosion, while confined pore pressure acting on the low-permeable surface layer induced the emergence of sand-boil and leak. Our findings underscore the crucial role of stratigraphic features on internal erosion processes and demonstrate the effectiveness of integrating geophysical investigations with numerical modeling for assessing internal erosion risks in engineering applications.