The Study On Mechanical Characteristics Of Cofferdam And Supporting Structure Under The Effect Of Tide

In recent years, with the rapid development of China’s coastal area and increasing exploitation of ocean, the number of coastal constructions is booming. Cofferdam is an important water-retaining facility in coastal constructions, it is practical to study the stress and deformation characteristics of cofferdam under the effect of tiding.Based on the opening and reconstruction project of Maluan seawall in Xiamen, this thesis expounds studies on stress and deformation characteristics of cofferdam and supporting structure under tiding. The study is carried out in two ways including numerical analysis and filed monitoring. This project locates at the inner area of Xiamen Bay. The tidal level in this sea area fluctuates considerably, the waves vary in small-scale, the foundation is very stable. According to tidal condition, the major factors effecting the cofferdam and supporting structures are tidal pressure, seepage in the cofferdam, and the minor factors are wave loading, strength reduction of clay caused by wave.The time scales of tidal pressure and seepage in the cofferdam can be calculated based on the actual situation of this project. The stress and seepage caused by tiding is unsteady, but varies slowly, therefore, the dynamic processes can be solved approximately by static method. The approach of complete fluid-mechanical interaction analysis is adopted in this thesis, and the manual calculation is the solving method of numerical analysis.In this thesis, numerical simulation of cofferdam and supporting structure is carried out using the explicit finite-difference program FLAC3D, to analyze the stress and deformation characteristics under tiding. The study includes:the effect of tidal pressure on excavation of foundation pit, the stress and deformation characteristics under different sea level, different tidal range, with bracing structure, and under the wave loading. The analytic result indicates that:the tidal pressure can effect the process of excavation; the tiding has slight effect on the stress and effective stress; the pore pressure varies in the shallow part of cofferdam because of the anti-seepage measure; the deformation of cofferdam, the stress and deformation of retaining piles vary obviously under tiding. The deformation of cofferdam and retaining piles increases when tide rises and decrease when tide ebbs, alternate circularly. When sea level rises over4m, the soil of cofferdam deforms plastically, and show no further variation. Bracing structure is very effective to limit the horizontal displacement of cofferdam and supporting structure, and the effect of wave loading is small enough to ignore.Comparing the results of numerical analysis and filed monitoring, the actual deformation characteristics correspond to analytic result.It illustrate that the analysis approach is applicable. The results of numerical analysis can indicate the stress and deformation characteristics of cofferdamand supporting structure under tiding.