Deeper piping erosion

Deeper piping erosion: Finding how to model it and what contributes to the emergence of a deeper pipe

Coevert, Steven (TU Delft Civil Engineering & Geosciences; TU Delft Hydraulic Engineering)

Aguilar Lopez, J.P. (mentor)
Kanning, W. (graduation committee)
van den Eijnden, A.P. (graduation committee)
van der Linde, E.M. (graduation committee)
Engels, Stef (graduation committee)

Delft University of Technology

Civil Engineering | Hydraulic Engineering

2023-06-29

The Netherlands is a country that is being threatened by water, both from the rivers and from the sea. The Dutch have built dikes to keep their lands from inundation. To ensure the strength and stability of these dikes, they are being assessed on the basis of several failure mechanisms. One of these failure mechanisms is Backward Erosion Piping, or piping for short. In piping, the current underneath a dike is strong enough to take soil particles with it. Tests on piping in tidal subsoil were conducted in the summer of 2021, where a pipe was found to have grown at greater depth than expected The occurrence of this deeper piping has rarely been seen before, let alone described. This lack of knowledge poses a potential safety risk, as it may underestimate the vulnerability of certain subsoil configurations. Therefore, the objective of this thesis is to develop a comprehensive understanding of deeper piping and identify the key parameters influencing its formation. To achieve this objective, a definition of deeper piping and its differentiation from conventional piping is established. Sub-mechanisms governing deeper piping are examined by analysing the forces responsible for grain movement and the forces that maintain grain stability. A Finite Element Model of the subsoil is constructed to quantify the driving forces within the subsoil, which, when combined with resisting forces, enables the determination of whether deeper piping can occur in a given subsoil configuration. To investigate the factors contributing to deeper piping, a series of simulations are conducted using this Finite Element Model. By varying the parameter values while keeping other factors constant, the influence of each parameter on the occurrence of deeper piping was examined. The analysis revealed that several key parameters significantly affect deeper piping formation, including cohesion force (𝑐), cohesion anisotropy (𝛼𝑐 ), permeability and thickness of the top layer (𝑘0 and 𝐷0, respectively), permeability of underlying layer (𝑘1), permeability anisotropy (𝛼𝑘 ) and representative grain diameter 𝑑𝑟𝑒𝑝. Also, it was found that the entrance configuration plays a large role in deeper pipe formation. These findings provide valuable insights into the mechanisms underlying deeper piping and enhance our ability to identify subsoil configurations that are prone to this phenomenon. These findings enhance the identification of subsoil configurations prone to deeper piping, thereby improving risk assessment and mitigation strategies associated with this failure mechanism.

Backward erosion piping
Finite Element Method
COMSOL Multiphysics
Sensitivity Analysis
Hertogin Hedwigepolder

http://resolver.tudelft.nl/uuid:72aff639-d044-4ab2-8383-8c2cb44e3176

Student theses

master thesis

© 2023 Steven Coevert