The maintenance and improvement of river embankments plays a crucial role in granting the safety and ensuring the quality of life of the inhabitants of the Netherlands. While the threat posed by storm surges has been greatly reduced since the implementation of the Deltaworks, riverine areas in the west of the country are characterised by the highest risk of flooding.
The use of relief wells is one of the viable solutions to improve the safety of river embankments against instability mechanisms such as uplifting. Throughout the Schoonhovenseveer-Langerak project (SLA), the implementation of a system of relief wells constituted one of the key measures to increase the safety of the embankment structure during high-water events of the river Lek. In the current study, the influence of relief wells was simulated employing a 3D coupled model built with the Finite Element software PLAXIS 3D. Using soil properties from former site investigations, a calibration was performed based on in situ pore water pressure measurements, in order to devise adequate boundary conditions. The safety assessment of the structure was then performed by applying a time-dependent high-water wave and employing strength reduction to yield a Factor of Safety. An intermediate 2D model was employed to examine the evolution in time of the Factor of Safety, the influence of mesh refinement on the safety results, and the shape and the location of the failure mechanism. By means of the 3D model, different design choices of the system of relief wells were tested and their influence on the stability of the structure and on the water discharge could be determined. A comparison between the results obtained in the 2D and 3D models showed that a 3D stability analysis does not necessarily yield a less conservative result than the 2D equivalent.
Comparing the values of the Factor of Safety obtained with time-dependent and stationary boundary conditions showed that the results obtained in the latter case are considerably more conservative, suggesting the potential benefits of a time-dependent fully-coupled analysis.