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In order to better interpret failure features of the failure of soil in front of tunnel face, a new three-dimensional failure mechanism is proposed to analyze the limit support pressure of the tunnel face in multilayered cohesive-frictional soils. The new failure mechanism is composed of two truncated cones that represent the shear failure band and a distributed force acting on the truncated cones that represents the pressure arch effect. By introducing the concept of Terzaghi earth pressure theory, approximation of limit support pressures is calculated using the limit analysis methods. Then the limit support pressures obtained from the new failure mechanism and the existing approaches are compared, which show that the results obtained from the new mechanism in this paper provide relatively satisfactory results.

Internal solitary waves (ISWs) can impose significant loads on offshore structures. During the past several decades, ISWs have led to a series of incidents. With large draughts, spar platforms can be affected by ISWs; therefore, the ISW effect should not be neglected during the design, installation and operation in areas where ISWs can occur. However, there is a gap in research into this area with only a few preliminary studies published so far.In this paper, a series of experiments are carried out with a spar platform model in a large-scale stratified tank at Shanghai Jiao Tong University to investigate interaction characteristics of ISWs. Based on a two-layer ISW theory, a simplified theoretical model is established for predicting the ISW loads on a spar platform. It is shown that the horizontal ISW loads consist of drag and inertia components, which can be calculated using the Morison's equation, while the vertical loads are mainly the vertical Froude-Krylov force, which can be obtained by integrating the ISW-induced dynamic pressure over the spar bottom.By fitting theoretical results with experiments, specific formulas are established to determine two empirical coefficients in Morison's equation under ISW conditions, which are different from traditional methods. The numerical results from this method show good consistency with experimental results on both the amplitude of the loads and the time varying characteristics. This research provides a practical theoretical model for predicting ISW loads on spar platforms.