Upper Bound Approach Of Limit Analysis And FE Numerical Analysis Of Stability Of Submarine Slope Considering The Wave-induced Pressure

Submarine slope instability is one of the most concerned and the most frequent geohazards in offshore engineering due to its serious threat to the marine structures and the life safety for human beings when developing and utilizing the marine resources. With increasing consciousness for marine development of our country, the marine strategy can play an increasingly significant impact on the economic construction and the research on the evaluation of the submarine slope stability can become one of the most popular issues in the research of marine geologic hazards. Nowadays, the most researches of the submarine slope statbility is based on the limit equilibrium method. But still, the method has some limitations and only the approximate solutions can be obtained by using this method.To evaluate the stability of seafloor slopes, in this paper, the limit state equation based on the upper bound approach of limit analysis incorporating strength reduction technique is established. Combined the strength reduction technique, the wave-induced pressure on the slope is applied as external loading. The minimum safety factor is obtained by searching the critical sliding surface. The effect of wave loading on the stability of seafloor slopes is quantified. Also, the large-scale FEM program ABAQUS is used to analyze this problem. Here, the analysis of submarine slope stability by2D elastic-plastic finite element method combined with the strength reduction technique considering the wave-induced pressure is obtained as the comparision of the results from the upper bound approach. On the basis of these, taking the rescue wharf in Xiamen as the engineering background, the FEM is used here to analyze its stability to make some constributions to the analysis of the submarine slope stability and to provide some designing basises of the submarine-slope strengthenning in the future.Focused on the theme of the submarine-slope stability in this paper, the key issues to be discuseed are as follows:1) The limit analysis of upper bound approach for submerged slopes under static water condition.Following rotational failure mechanisms proposed where the sliding surface is described by the log-spiral equation, the limit state equation is established combined with the strength reduction technique,in which the pore pressure in slopes can be considered as one kind of external loads in the virtual work-rate equation. The evaluation of the submerged slope can be quantitatively analyzed by searching the minimum safety factor and the critical sliding surface. 2) The analysis of stability of submarine slopes considering wave-induced pressure by limit analysis of upper bound approach.The simplified wave-induced pressure based on the linear wave theory is used in this paper to established the limit state equation of the sumarine slope considering the effect of waves. Discuss the differential of the safety factors and the critical sliding surfaces obtained by the two distinct ways to exert the wave-induce pressure (exert the pressure on the CSS under static water condition and exert it directly in the virtual work-rate equation). And also, the effect of the parameters of wave (height and length) and the water depth on the stability of submarine slopes are deeply discussed.3) The stability analysis of submarine slopes based on the finite element method combined the strength reduction technique.To analyze the submarine slope stability considering the wave-incduced pressure, the2D elastic-plastic finite element analysis is used. In this calculation, the wave-induced pressure is based on the theory of the linear wave. The effect of wave parameters and the water depth on the positions of CSS are discussed by compasion of the results from FEM and the upper bound approach. On the basis of these, considering the wave effect, the two dimensional SSR-FEM is used here to analyze the stability of the rescue wharf in Xiamen to obtain a preliminary realization of the submarine landslides in practical engineering problems.