Seepage Analytical Model Of Bucket Foundation During Suction Penetration

The bucket foundation seems a gravity foundation with skirts, whose working mechanics and structure characters are similar to suction pile. Bucket foundations are a relatively new type of foundation used to support offshore structures. Comparing with traditional pile structure, bucket foundation has some special advantages such as bearing capacity, construction convenience and wide usage, so more attention is paid to bucket foundation in ocean engineering. The foundation can penetrate into sea bottom when pumping water out of the foundation chamber while the formation of seepage flow field inside soils around buckets. Therefore, the study on seepage flow is the basic problem for bucket foundation. This paper is concerned with the setup of calculation model of seepage flow field.According to research materials and results, the components of sub-sea soft soil, micro-structure of soil particle, the characteristic of soil deformation and porosity property are analyzed to study the porosity property, category the porosity of sub-sea soil, and to acquire the changes of porosity property during the action of seepage forces.The strain of soil acted by seepage forces is divided into the volumetric strain of soil particle caused by self-deformation and soil volumetric strain caused by geometric deformation of soil skeleton. In this dissertation, J₂ flow theory and discrete element method are put into setup of soil constitutive relationship model. Firstly, the isotropic hardening principle in J₂ flow theory is used into the constitutive relationship model of soil particle deformation. Secondly, discrete element method principle is used into the constitutive relationship model of soil skeleton deformation. Lastly, the two constitutive models are put together into constitutive relationship of total deformation.The physical parameter of soil dynamic model put into the description of bucket foundation during suction penetration improves the traditional calculation method. According to the definition of physical parameter, the volumetric strain of soil skeleton calculated by discrete element method, volumetric strain of soil particle calculated by J₂ flow theory, and the sum of two volumetric strains are set as the soil instant strain for setting up the dynamic variables of soil physical parameter.According to the structure style of bucket foundation and soil stress change around the buckets, effective stress principle is modified for usage of bucket foundation. The penetration resistance formula of bucket foundation is studied again in the paper and influence on resistance caused by soil seepage softening is analyzed, for the formula is the main part of stress equations. So the penetration resistance formula is modified by considering the influence of soil soften caused by seepage to resistance.At last, solid-fluid coupling seepage mathematical model for suction penetration of bucket foundation is formed with stress equation and seepage equation formulated by conservation of mass and seepage motion equation and the solution conditions are given for the seepage model. At last, effectiveness and utilization of the given models are tested by some calculating examples.