Pore Pressure Response In Soil Around Excavation Sibjected To Water Level Fluctuation

With the development of economy and the acceleration of urbanization in China, there are more and more high buildings and infrastructures have been or will be built. Meanwhile, the environment near excavation also becomes increasingly complicated. In recent years, excavations nearby sea or river emerges in large numbers, which are obviously different from the tratidional excavation projects far away abundant water resource, they are significantly affected by irregular or periodical water level fluctuation due to wave and tide. Therefore, behavior of excavation subjected to water level fluctuation is a new problem accompanied with new engineering practice. The focus of the research is the pore pressure response around excavation because it is the basis for further research, such as the stability of excavation, the deformation and internal force of supporting structure.Firstly, two simplified seepage analysis models are proposed for excavation affected by groundwater fluctuating in surface aquifer around excavation by the sea and water fluctuating above seabed around excavation in the sea. The corresponding FEM analysis models through PLAXIS software are presented. Then the numerical analysis on the seepage characteristics around excavation affected by water level fluctuation are carried out, and the effects of key factors are analysed thoroughly. Based on the excavation located in Lingding Ocean of the Hong Kong-Zhuhai-Macau Bridge project, the influence of water level fluctuation on the stability of gravity retaining wall is studied. Finally, by dividing the seepage area around excavation into several zones and employing Laplace and Fourier transformation, semi-analytical solutions of soil pore pressure response near excavation under several simplified watel level fluctuation conditions are deducedOn the basis of the study, the following conclusions can be drawn.1. The amplitude of relative excess pore pressure attenuates along the shortest seepage path (i.e. the seepage path along retaining wall from active side to passive side). When the groundwater level fluctuates within the surface aquifer, the phase lag in soil around excavation is significant2. when groundwater level fluctuates within surface aquifer, the larger the comprehensive coefficient θ, which is related to consolidation coefficient, thickness of seabed and wave or tide period, the smaller the amplitude of relative pore pressure around excavation is. However, when water level fluctuates above sea floor, the larger the θ, the larger the amplitude of relative pore pressure in the active side of excavation is, while, the smaller the amplitude of relative pore pressure in the passive side of excavation is. What’s more, the relative pore pressure in steady seepage condition (corresponding to0=0) is the extremum of amplitude of relative pore pressure for dfifferent θ.3. The larger the propagation coefficient β(i.e. the smaller the saturation coefficient is), the smaller the amplitude of relative pore pressure and the larger the phase lag is.4. The influence of excavation width, anisotropic permeability and the distance from the bottom of retaining wall to the impervious boundary on pore pressure response around excavation is significant.