ABSTRACT

An advanced numerical analysis in this paper is two-dimensional dynamic non-linear finite element method (Takatani et al., 2005, 2008) based on the effective stress theory in order to simulate a sweeping behaviour of shallowly-embedded pipeline on carbonate sandy soil under undrained condition. In this finite element analysis, a non-linear relationship between shear stress and shear strain of soil element is accurately expressed by a multi shear spring model (Towhata and Ishihara, 1985) and the Masing rule for loading and unloading curves is employed so as to adjust the amplitude of hysteresis damping for the multi shear spring model. Also the cyclic mobility model (Iai et al., 1990), which is of a generalized plasticity-multiple mechanism type, is adapted to simulate excess pore water pressure. Pore fluid is assumed to be imcompressible, and also the viscous boundary technique (Lysmer et al., 1969) is used to create the infinite of seabed soil in this analysis. There are three governing equations of a kinematic equation between soil and pipeline, pore water input/output balance equation in each pore fluid element, and dynamic water pressure wave propagating equation for pore fluid. Pore water pressure can be expressed by an increment of volumetric strain of soil skeleton because of undrained condition, and also dynamic water pressure wave propagating equation for pore fluid can be represented by a technique that the effect of pore fluid

existence can be taken into consideration by applying an additional mass of each pore fluid element to the soil-structure kinematic equation.