Reliability Analysis For Estimation Of The Inclined Sea Dike Crest Elevation

Along the coastline of China, many sea dikes are constructed to protect the safety of their backlands. The typhoon attacking and associated surge flooding sometimes cause heavy loss of lives and properties. Wave overtopping is one of the main reasons that cause the failure of sea dikes. It is significant to rationally calculate the crest elevation of sea dikes for disaster prevention and mitigation.At present, there is no national code for the design of sea dikes. However, there exist different design criteria in coastal provinces. In these criteria, the sea dike crest elevation is the sum of the design high tide level, wave run-up and the safety free- board. The design high tide level is estimated by annual maxima frequency analysis method recommended by Code for Sea Port Hydrology in China. Actually the annual maximum high tide level used for frequency analysis is combined with astronomical tide level and storm surge elevation. But the joint action caused by there two components is commonly neglected to considered in the frequency analysis of the design high tide level. In the mean time, the safety free-board is given by experience to calculate the crest elevation in local design criteria.On the basis of long term observed data, a novel procedure is presented to compute the sea dike crest elevation with Design Point Method in generalized random space. In this procedure, a proper wave run-up equation is selected and applied through a review of related references. Different extreme value distributions, for example Pearson-III distribution, log-normal distribution, Gumbel distribution and Weibull distribution, are adopted to fit random variables. The sea dike crest elevations corresponding different return periods are estimated by solving the limit state equation. The proposed procedure to calculate the crest elevation of sea dike has been testified by practical examples, such as the dikes built along the banks of both Laizhou Gulf and Huanghai Sea. The main contents of this paper are as follows:(1) To summarize and analyze the domestic and foreign wave run-up formula, such as VDM method, method in Code for Sea Port Hydrology and the method in Code for Hydraulic Dike Design.(2) To summarize and analyze frequently applied reliability methods, such as the first-order second-moment method, response surface method, Monte-Carlo method and random finite element method. The corresponding programs are compiled with MATLAB software.(3) The crest elevations of typical sea dike cross section are separately calculated by the local criteria method and the reliability method. Results show that the presented method is feasible and reasonable to determine the crest elevation.