Sellmeijer in the northern Maasvallei

Abstract

The applicability of the Sellmeijer design rule to Limburg dike sections near Well, Hout-Blerick, Buggenum, and Thorn was investigated in this thesis. This was accomplished by building a finite element numerical model, in COMSOL Multiphysics, to assess the piping in the hydrogeological systems of the research locations. The proposed model is composed by combining several groundwater and piping model principles, schematizing dike cross-sections, and calibrating the model. The schematization choices that define the model geometry of the average pipe cross-section are critical. It was decided to apply a fracture flow pipe cross-section and the piping assessment was performed iteratively for multiple pipe height values, because the true pipe height is unknown. The pipe height is expressed as a function of the number of grains and the representative grain size.

According to a deterministic assessment, which was performed analytically using multiple versions of the Sellmeijer design rule and numerically using the proposed FEM model, piping does not occur at the research locations Well, Hout-Blerick and Thorn. Piping is theoretically possible at Buggenum, but only with a very small pipe height, making it appear very unlikely. The assessment also revealed that the critical head determined by using revised Sellmeijer design rule (2021) is conservative for the examined dike sections in Limburg. Furthermore, it is discovered that the original Sellmeijer design rule with the new geometry factor (1988/2011) produces critical heads that are similar to the results of the revised Sellmeijer design rule (2021) multiplied by 1.8, which is the current design rule used to assess piping in Limburg.

The Sellmeijer design rule (1988/2011) was stochastically evaluated to determine how the design rule changed when calibrated to Limburg parameter values. 1000 unique randomly generated dike cross-sections were evaluated on piping using the proposed FEM numerical models. The unique dike cross-sections are made up of a random combination of model parameters that were sampled from a uniform distribution using Latin Hypercube Sampling (Olsson et al., 2003). The randomly generated dike cross-sections that demonstrate piping for a realistic pipe height, were used to re-calibrate the Sellmeijer scale factor. Using a linear regression, it was demonstrated that the scale factor corresponding to the broadened application range (including Limburg parameter values), of the Sellmeijer design rule, is 1.56 times greater than the original scale factor. This means that the original Sellmeijer design rule with the new geometry factor (1988/2011) and the additional factor of 1.56, can be applied to (Limburg) dike sections, for which the model parameters fall within the newly set parameter application ranges (e.g. 100 µm ≤ d70 ≤ 900 µm).