Piping in the Maasvallei

Abstract

One of the failure mechanisms for water retaining structures is piping. Piping is an internal erosion
mechanism creating hollow spaces (pipes) underneath, for example, a dike as a result of the transport
of soil particles due to seepage. The formation of pipes can cause collapse of the structure once the
erosion process reaches the outside of the dike. This study focusses specifically on the possibility of
the occurrence of this failure mechanism in the Maasvallei area. The Maasvallei covers the area of the
Maas roughly between the Dutch towns Roermond and Mook. The early signs of piping in the form of sand boils are frequently observed during periods of high water levels in the Dutch rivers. Although the total collapse of a dike in the Netherlands due to piping has
not occurred in the past decades, the frequent observation of the early signs of the piping process
has resulted in the inclusion of the piping failure mechanism in the Dutch legal safety assessment
regulations for water retaining structures. During recent high-water periods in 2011 and 2012 sand boils
were observed along several Dutch rivers except at the dikes along the Maas. The striking absence of
sand boils in the Maasvallei area raised the question if the failure mechanism piping is relevant for this
specific area. In the recent assessment of the Dutch dikes, many of the dikes along the Maas in Limburg were found
to be insufficiently safe against piping. The dilemma then becomes clear: the lack of early signs of
piping contradicts the outcome of the safety assessment. Resources could be saved if the dikes do
not need to be reinforced for piping, however, the safety should not be compromised. Within the thesis this dilemma is studied. The main question that is answered is: Is dike-failure due to piping realistic in the Maasvallei?