Seepage-induced backward erosion is a complex and significant issue in geotechnical engineering that threatens the stability of infrastructure. Numerical prediction of the full development of backward erosion, pipe formation and induced failure remains challenging. For the first time, this study addresses this issue by modifying a recently developed five-phase smoothed particle hydrodynamics (SPH) erosion framework. Full development of backward erosion was subsequently analysed in a rigid flume test and a field-scale backward erosion-induced levee failure test. The seepage and erosion analysis provided results consistent with experimental data, including pore water pressure evolution, pipe length and water flux at the exit, demonstrating the good performance of the proposed numerical approach. Key factors influencing backward erosion, such as anisotropic flow and critical hydraulic gradient, are also investigated through a parametric study conducted with the rigid flume test. The results provide a better understanding of the mechanism of backward erosion, pipe formation and the induced post-failure process.

Double-layer dike foundation is composed of a weakly permeable overlying clay layer and a highly permeable underlying sand layer, which is one of the most common stratum types in dike engineering with the highest probability of catastrophic damage, and the main danger is backward erosion piping. Existing research on backward erosion piping of double-layer dike foundation has not fully considered the influence of the exit on the erosion process. Therefore, a self-designed test device is used to assess the influences of the size, position and type of different exits, and the circular exit is connected with the slot exit via the exit area to explore the critical identification conditions and the pipe development mechanism toward the upstream direction under different exit geometry conditions. The results show that both the local and global hydraulic gradients borne by the exit are inversely proportional to the exit area and are less notably affected by the location of the exit. The development process of slot exit pipes differs from that of circular exit pipes, and pipes are usually developed alternately at the two corners of the exit near the upstream end and then converge into one pipe. The average pipe depth and width are proportional to the exit size and the seepage length. With increasing average pipe area of the slot exit, pipes develop more rapidly after head enhancement, and the damage to the dike foundation increases.

Bei dem Beitrag handelt es sich um die erweiterte Fassung der gleichnamigen Keynote Lecture auf der 4. Bodenmechanik Tagung im Rahmen der Fachsektionstage Geotechnik, die auf Anregung der Fachsektionsleitung auch in der Zeitschrift geotechnik veroffentlicht werden soll. Bei den Phanomenen der inneren Erosion in durchstromtem Boden und in Erdbauwerken geht es um das Losen, den Transport und die Ablagerung bevorzugter Fraktionen mit der Folge einer anderung der Bodeneigenschaften. Die Phanomene der inneren Erosion werden als Kontakterosion, Suffosion, Kolmation und ruckschreitende Erosion charakterisiert. Die Kinematik dieser physikalischen Prozesse ergibt sich mit der Energie einer Sickerstromung aus der Bewegung des Einzelkorns im Porenraum, den moglichen Freiheitsgraden beim Transport. Der Artikel gibt einen uberblick uber die Art und Bedingungen der verschiedenen Phanomene sowie uber deren spezifische Kinematik innerhalb der Bodenstruktur. Die relevanten international verwendeten Nachweismethoden und Kriterien werden aufgefuhrt und in ihrer Aussagekraft bewertet. Die kennzeichnenden Einflussparameter werden aufgezeigt. Fur die einzelnen Phanomene der inneren Erosion werden Strategien zur Bewertung und Beherrschung des Erosionsrisikos diskutiert. Phenomena, kinematics and risk assessment strategies of internal erosionInternal soil erosion due to seeping water in natural sediments as well as in earthworks can lead to a significant change in soil properties and could even destroy the structural integrity. The physical process of erosion always is induced by loosening, migration, and deposition of predominant fine particles within the soil structure. Depending on the kinematics, the phenomena are divided into contact erosion, suffusion, colmation and backward erosion piping. The kinematics is controlled by the energy of a seepage on the one hand, on the other by the degrees of freedom and the boundary conditions of an individual grain movement within the pore space. This article provides an overview of the characteristic, specifics, and conditions of the different phenomena considering their kinematics within the soil structure. Internationally used approaches and methods of assessment are listed, their significance and their limitations will be evaluated. The impact parameters that control the different processes are shown. Strategies for assessing and controlling the risk of structural damage are discussed for the different phenomena of internal soil erosion.