Seabed instability surrounding an immersed tunnel is a vital engineering issue regarding the design and maintenance for submarine tunnel projects. In this study, a numerical model based on the local radial basis function collocation method (LRBFCM) is developed to evaluate the seabed behaviour in a marine environment, in which the seabed is treated as the porous medium and governed by Biot's "u − p" approximation. As for the flow field above the seabed, the VARANS equations are used to simulate the fluid motion and properties. The present model is validated with analytical solutions and experimental data which show a good capacity of the integrated model. Both wave and current loading are considered in this study. Parametric studies are carried out to investigate the effects of wave characteristics and soil properties. Based on the numerical results, the maximum liquefaction depth around the immersed tunnel could be deeper under the wave loading with long wave period (T) and large wave height (H). Moreover, a seabed with lower permeability (K s ) and degree of saturation (S r ) is more likely to be liquefied.

The study on the relationship between the soilmass deformation and water seepage under certain stress in North China was conducted through combined tests of the consolidation deformation and water seepage. The results showed that the actual deformation of the clay soil under stress is greater than the deformation induced by the seepage. On average, the deformation induced by seepage was about 60% of the actual clay deformation under stress. The actual deformation of sandy soil, however, is less than the deformation induced by seepage. On average, the seepage-induced deformation was approximately 125% of the actual sandy soil deformation. These results indicated that the sandy soil did not have complete plasticity. Clay had the highest amount of water seepage and deformation, while silty soil, calcareous highly cemented clayed soil and sandy soil had less water seepage and deformation. The underlying mechanisms were also discussed. The results of this study contribute to the understanding of land subsidence mechanism and rough estimation of groundwater exploitation.

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