Large parts of the Netherlands are situated below sea level, making the country vulnerable to flooding. To prevent flooding, dikes form the most critical measure against flooding. Because of the rising water level and more extreme weather events dikes are being reinforced. One of
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Large parts of the Netherlands are situated below sea level, making the country vulnerable to flooding. To prevent flooding, dikes form the most critical measure against flooding. Because of the rising water level and more extreme weather events dikes are being reinforced. One of the most important failure mechanisms of dikes is backward erosion piping (BEP). To prevent this failure mechanism from occurring, heave screens can be used as a vertical impermeable barrier at the inland toe of the dike. While traditional steel sheet piles have been the standard. Lately, plastic heave screens are more used as an innovative, sustainable, and cost effective alternative. However, the lower bending stiffness and strength of plastic require different installation techniques, often in the form of a steel mandrel to guide the piles to their design depth. This mandrel is a steel motherplate which is used to drive the plastic sheet pile safely into the ground. The installation process and the properties of plastic provide new challenges, such as mandrel induced soil disturbance and interlock failure, that are typically neglected in current assessment practice, which assumes ideal, continuous, and undamaged conditions.
The primary objective of this research is to examine how the installation process, or faults that occur during this process, influences the hydraulic effectiveness of plastic heave screens against BEP. Using a representative case study of a Dutch river dike section prone to piping, this study uses a numerical modelling strategy using PLAXIS 2D and 3D. The methodology evaluates the sensitivity of the system to localized defects by analysing key hydraulic indicators: groundwater head distribution for global heave safety, vertical flow velocity, and vertical hydraulic gradients.
Numerical results demonstrate that installation induced faults have a measurable impact on hydraulic performance. 2D analysis reveals that mandrel induced disturbed zones with higher permeability act as a local relief well. This leads to a reduction in hydraulic head at the screen tip, which increases the calculated safety factor for global heave. However, this venting significantly increases vertical flow velocities within the disturbed zone, heightening the risk of internal vertical erosion.
3D modelling is essential for capturing localized delocking, which triggers 3D flow towards the fault that 2D plane-strain models fail to represent. While global head remains largely unaffected by a single isolated delocked sheet pile, the local head at the gap increases significantly, causing local heave safety factors to drop below the required threshold. Furthermore, the study investigated multiple gaps and concluded that clustered defects pose a significantly greater risk than isolated imperfections, as their zones of influence overlap and amplify negative hydraulic consequences.
In conclusion, the hydraulic resistance of plastic heave screens is influenced by installation quality and three dimensional flow effects. It is recommended that future research focuses on the governing mechanisms of vertical fluidization and the development of more realistic 3D representations of pipe systems to bridge the gap between execution reality and safety assessment.
