In order to ensure the safety and reliability of the submerged tunnel covering layer at the junction of an artificial island and tunnel under extremely bad conditions, the wave current characteristics and the stability of the protective structure in the variable slope section were studied. By conducting model tests, the coupling effect of wave and current is revealed in this study. The hydrodynamic field, including the varying angles between waves and currents, is simulated in the model test. The ratio ($H_{\mathrm{s}}^{\prime }/H_{\mathrm{s}}$) of the wave height and the ratio ($U^{\prime }/U$) of the velocity with and without the existence of a current, the relative velocity (U$/C$), the wave steepness ($H_{\mathrm{s}}/L$), the relative water depth ($d/L$) and the angle ($\alpha$) between wave and current are obtained, and the corresponding calculation expression is derived, by checking the test results, the empirical formula can better predict the changes of wave height and water flow after wave current coupling. The stable weight of the surface protection rock is obtained through an optimization test. Based on the relationship between the stable weight of the protection rock and the wave height under the wave–current coupling effect, a modified expression for calculating the stable weight of the armor block is derived. The modified calculation method can support estimating the stable weight of the armor rocks of an overburden structure of a similar immersed tunnel under the wave–current coupling effect. This study can not only solve the practical problems of major projects of the Shenzhen–Zhongshan channel but also provide valuable basic data and technical support for the construction of overburden of subsea-immersed tube tunnels in the future.

The bay of Bengal is an important sea area of the 21st century Maritime Silk Road. Systematic analysis of the hydrodynamic and sediment characteristics of the bay of Bengal is conducive to the development and implementation of offshore and coastal projects in the bay of Bengal. In this paper, based on the historical reanalysis data of ECMWF and the observed data of several hydrological stations along the east coast of Bangladesh, including wave, tide level, tidal current and sediment data are verified and assimilated, and the characteristics of wind wave, water level, tide and sediment along the east coast of Bengal are analysed. The hydrodynamic and sediment conditions in the bay of Bengal are generally characterized by “strong tide, strong wave and high suspended sediment concentration”. The bay of Bengal is easily affected by cyclonic storms, which causes a great increase in storm surge. The above situation will lead to the complicated sediment erosion and deposition of storm surge, strong wave and strong tide and high suspended sediment concentration. At present, there has no deep-water port and coastal power plant located in the bay of Bengal. Whether to build a deep-water port or how to transfer at sea should be paid attention to or studied in depth.

Based on the occurrence of floating and fracture accidents of FRP pipes on muddy seabeds in practical engineering combined with the water intake and drainage project of the 2 × 660 MW coal-fired power plant in the second phase along the coast of Vietnam, a model test study was carried out. The laboratory simulated the FRP pipe conditions during the construction and operation periods by configuring different densities of silt. The experiment results obtained are as follows: the FRP pipes floated up in the mud during the construction period; the thickness of sediment deposition when the FRP pipes are lifted up, as well as the entire lifting process time and maximum force, are all within 2 h and 70 kN/m; after adopting a cover layer design section during the operation period, the FRP pipes in the silt remain stable while obtaining a maximum force of 15 kN/m; and based on the experimental results, an empirical formula for the stress on FRP pipes and was derived and measures for FRP pipe stability were proposed. The research results not only solve practical problems in water intake and drainage engineering but also provide technical support for the promotion and application of FRP pipes.

The design water level calculation methods in the Chinese and foreign codes are different. The design high and low water levels and extreme high and low water levels in the Chinese norms are calculated using historical cumulative frequencies with tide level data of not less than 1 year and 20 years, respectively. In foreign norms, the average high and low tide levels of spring tides are mostly used as the design high and low water levels, and for the sea areas lacking long-term measured data, the water level combination method is mostly used to determine the extreme water levels. This paper compares the results of different methods used to calculate the design water level using the Chittagong Power Plant in Bangladesh as an example. The calculations show that it is safer to use the tidal eigenvalue method to determine the design high and low water levels, and that the Water Level Combination Method is more suitable for extreme water level determination than Bangladesh National Building Code.

Due to the depletion of near-shore resources and the complex environment of offshore deep-water open port construction, a new barrel-pile foundation composite structure wharf is proposed. In order to provide technical support for the engineering design and application of the new structure, research is carried out on a physical model. Through setting up a series of group tests, on the basis of fully understanding the wave impact characteristics of the wharf panel of the new structure: (1) the relationship between the wave crest height, impact force, and various influence factors is established; (2) a calculation method and formula are put forward (compared with the physical model test data, the calculation formula results have good accuracy); (3) according to the formulas of wave crest height and panel impact force, a determination method for the wharf surface elevation of the new structure is given. In addition, due to the limitations of the test conditions, it is suggested that the physical model should be further verified for a complex transverse and longitudinal beam structure or extreme sea conditions, such as traveling wave breaking and wave inundation of the wharf.

Experimental Study on Calculation Method of Drainage Capacity of Drainage Facilities Affected by Overtopping on Artificial Island: The drainage capacity design of offshore artificial island and inland urban drainage facilities have a great differences in the boundary conditions involved. Therefore, in order to ensure the safety and reliability of the drainage facilities of the Shenzhen-Zhongshan channel’s East artificial island under extreme weather conditions, the coastline of the Southwest open section of the artificial island is identified as a subject for carrying out the research study. This island is affected by offshore waves and the superposition of rainstorms, therefore the calculation method of drainage capacity of artificial island drainage facilities is demonstrated in the article. Through the physical model testing based on soft computing techniques, some recommendations are suggested for preserving the environment, where the optimization schemes are meeting the design requirements of wave and landscape based on correlations between them. Secondly, the adjustment of drainage capacity is suggested to analyze the overtopping of waves on the island and then the final scheme meeting the drainage capacity is obtained. By introducing the comprehensive influence coefficient of overtopping volume and current velocity caused by overtopping under the action of superimposed waves, a new calculation method and simple calculation formula suitable for the drainage capacity in the artificial island are proposed. The proposed method is verified by the drainage capacity test results of the southeast shoreline. The results show that the proposed method has good accuracy and can provide reference for the design and estimation of drainage capacity of similar projects to preserve the environment. The research results based on mathematical problems in engineering not only solve the practical problems of major projects of Shenzhen China channel but also provide valuable inputs for similar projects.