| The land reclamation activities in China have been kept developing rapidly in recent years.However,the traditional alongshore reclamation manner is not conducive to the scientific,harmonious and sustainable utilization of precious tidal fiat resources in China,and its adverse effects on marine ecological environment have been more and more recognized. The scientific and appropriate utilization of sea resources will thus be the developing trend of land reclamation,as stricter control will be exerted to the way of alongshore reclamation. Meanwhile,building artificial island is going to be the primary manner to reclaim land from sea in the future.Compared with the traditional way of reclaiming land from beaches,building artificial island should be given with more attention to the ocean hydrological and dynamic changes, the mutual implication between artificial island and marine environment,and the geomorphic change of coastal landform etc.This paper firstly makes an investigation and research on the current situation and developing trend of artificial island,and introduces as well the currently applied analysis and prediction methods for beach evolution.By taking a practical example of a typical artificial island under construction,this paper further elaborates the analysis methods on beach stability of artificial island by various technical means,such as coastal landform evolution analysis, numerical tidal simulation as well as physical model test etc.Analytical conclusions are herewith drawn for the reference of artificial island design.This aforesaid artificial island,under strict regulations of sea environment protection,is built for petroleum exploration and development at shallow sea.The island is situated on silty seabed with interlaced distribution of shoals,deep troughs and sand ridges.The underwater topographic conditions are complicated around the sea area,while beach instability may also happen.In addition,the impact of building this island on Caofeidian Trough shall also be considered.Therefore,the artificial island has to be built with appropriate plane layout, making full advantages of the existing topographic and hydrological conditions,paying attention to ecological and environment protection,and minimizing its impact on waters and tidal current to an optimal level.Based on the analysis of available data,this paper presents a preliminary analysis on marine dynamic geomorphology and beach stability of the sea area,shows in macroscopic view the basic features of marine dynamic geomorphology,erosion and sedimentation changes,sediment movement characteristics as well as beach stability under nature conditions at the planned site,and predict the changes which may happen when the artificial island is built.This paper sets up calculation mathematic model for tidal currents at the project site and describes by calculation the impact on neighboring and regional flow fields before and after the island is built.The basic model equation is the one of 2D tidal current movement under any curvilinear coordinates,solving by Finite Differential Method(FDM) with staggering grids and Double-Sweep-Implicit(DSI) Method.Water level distinguishing method is applied to calculate the exposure and immersion process of the beach within calculation scope,and thus a good simulation of the process is made.This paper also makes a study on physical model test and researches on stability of the artificial island by means of various study and test methods,such as in-situ site conditions analysis,fixed bed tidal model test,movable bed wave and tide model test,and movable bed wave model test etc.The study results of this paper provides scientific basis for engineering design, especially demonstrating the validity of the plane layout of artificial island,the length and field angle of submerged protecting dike,and flow changes in front of landing point etc. Optimizing solutions are also proposed.Compared with the normal application of one or two study means to artificial island, many more advanced technical means in the field of beach evolution study are used in this paper,such as coastal geomorphology evolution,mathematic model test and physical model test etc.Each method is independent but applied interactively and testifies each other.The study results are more reliable.Considering the limitation of model test field and the need of sand selection,the integrated physical model needs to be distorted normally.However,the model should be undistorted in order to satisfy similar wave conditions.For solving this conflict,this paper takes different model scale in accordance with different test items during conducting the fixed bed physical tide model test as well as movable bed physical wave and tide model test,which gives a good simulation of current and wave impact on beach stability of the artificial island.The study results of this paper have been successfully applied to the construction of the said artificial island,while the study methods utilized in this paper could be taken as reference for the building of similar artificial islands. |
