Opdrijven, opbollen, opbarsten

Abstract

Internal erosion is a frequent cause of dike failure, also known as piping or backward erosion. Uplift is considered a submechanism of internal erosion, together with heave and piping, where all three submechanisms must occur for the dike to reach a failure condition. The principle of the uplift phenomenon is straightforward: it occurs when high pore water pressures in the aquifer lift the cover layer, which is located at ground surface. If the pressure is great enough, the cover layer begins to float ('opdrijven'), and may also bulge ('opbollen') or crack ('opbarsten'). Currently, the assessment for uplift is based on a vertical equilibrium, which relates to a floating condition of the cover layer. The forming of an exit point for concentrated seepage is presumed to happen simultaneously with the increase in uplift pressure and is therefore not explicitly considered in the current assessment. This thesis aimed to investigate in what way the uplift assessment may be improved, both to describe the complex behavior better and to decrease the need for costly countermeasures. The evaluation of uplift was conducted in two parts: by making explicit what the causes of uncertainty are in the current assessment, as well as by proposing a new model to describe the complete uplift behavior better. It is recommended to evaluate the ‘floating’ and ‘bulging-cracking’ phases directly. In the ‘bulging-cracking’ phase, the forming of an exit point can either occur by a tension or shear failure.