Fatigue of asphaltic dike revetments under wave loading: validation and improved modelling

Abstract

In the Netherlands, 600 km of the sea dikes are protected by an asphaltic revetment that has to resist considerable wave loads with a significant wave height of up to 4.5 m. The subsoil is normally sandy, and the asphalt layer acts as a protection against erosion. The asphalt layer can fail as a result of fatigue due to repeated loading under storm conditions. In case of very high wave loads, the asphalt can fail after a few large waves. Ageing of the asphalt has a large effect on the resistance against fatigue. Therefore, periodic monitoring is prescribed by law. This monitoring consists of: falling weight deflection measurements, lab testing, radar measurements, visual inspection and calculations with the software program ‘Wave impact’ (‘Golfklap’) in order to determine the strength under storm conditions. The subsoil bearing capacity determines how the asphaltic revetment deforms under wave loading. It is still unsure how the soil will behave and failure mechanisms may occur that are different from fatigue due to elastic bending, the latter being part of the current approach. A first step to validation consisted of finite element modelling that was compared with experiments on medium scale (scale 1:4). In these experiments, the wave attack was simulated by a mechanical system that was placed on a 5 cm thick asphalt plate on a sand layer. The deflection of the asphalt was measured. Crack development was detected by means of strain gauges. It was found that – as a first approximation and excluding extreme wave loads – the fatigue behaviour of aged asphalt on a typical sandy base under wave attack can be described with a combination of a relatively simple elastic–plastic response to wave loads and a special fatigue line that takes into account the flexural strength of the aged asphalt.

Keywords:

• asphaltic revetments
• wave attack
• fatigue
• modelling
• lab-testing

Acknowledgement

The research reported here was part of the WTI-2017 programme as commissioned by Rijkswaterstaat.