Reliability and optimised maintenance for sea defences

摘要

Sea defence structures are valuable assets hence requiring viable and diligent asset management and maintenance strategies in order to ensure their integrity and functionality. It has been well documented that rising sea levels due to climate change together with the aggressive environment to which coastal defence structures are subjected can lead to serious defects compromising the integrity of the structures. This paper presents a method for quantitatively assessing the risk of wave overtopping of sea defences, analysing the probability of failure of the structures under future hydraulic and structural conditions and providing cost-effective maintenance planning during the service life. Typical failure mechanisms in an earth sea defence are considered for reliability analyses, namely erosion of dyke crest and landside slope by wave overtopping, piping in the underlain water-conductive layer and uplifting of impermeable layer behind the structure. The stochastic deterioration model based on the gamma process is adopted to represent the settlement of dyke crest height and the deterioration of seepage resistance. The time-dependent reliability of the earth dyke is analysed by using a Monte Carlo simulation method to give probability of failure over time. Optimal repair planning during the service life is determined by optimising the balance between the risk of failure and the costs for maintenance. The numerical results for the example typical earth dyke section show that overtopping is a dominant failure mechanism with significantly increasing failure probability over time. The optimal repair time largely depends on the deterioration rate of structural resistance and the relative cost of preventive maintenance.