Stability Analysis Of Submarine Slope Under Complex Environment

Submarine landslide as one of common marine geological hazards in the delta or continnental shelf area, is a serious threat to smarine structures and the life safety for human beings. Nowdays, the research on submarine slope stability and landslide mechanism has bocome one of the most popular issues in the research of marine geologic hazards. Currently, the limit equilibrium method (LEM) has been one of the most popular approaches to assess the stability of seabed slope. But still, the method has some limitations and only the approximate solutions can be obtained. Herein, based on the upper bound approach of limit analysis, the stability analysis of submarine slopes subjected to linear wave loading or secend-order stokes wave loading are conducted. Furthermore, consisering the influence of soil diturbance, heterogeneity of soil strength and muliti-layer, the stability of submarine slope under complex environment is evaluated. The main research work done in this paper include following parts.1. Based on the unper bound the theory and incorporating the log-spiral failure mechanism, the external work rates produced by gravity and internal energy dissipation for submarine slopes under static water are derived. Combined the strength reduction technique with optimization method, both the factor of safety and the critical sliding surface are solved. To verify the correctness of the method, various examples are carried out.2. Considering wave load, incorporating the linear wave theory, the paper derives the external work rates produced by the wave-induced pressure on the sloping seabed and the self-gravity of sliding body. The limit state equation of submarine slope under linear wave loading is established through the external work rates being equal to the internal energy dissipation rates along the critical sliding surface. On the basis of this, the factors of safety at the different time under one-wave period are obtained by using the optimization method combined with numerical integration. Finally, the stability of submarine slope under wave conditions such as various wave parameters (i.e., wave length, wave height and water depth) and the special case of slope length no more than one wave length, is discussed in details.3. With the secend-order stokes wave theory, the upper bound approach of stability of submarine slope under nonlinear wave loading is established. On the basis of this, With the clayey sloping seabed as a research object, the paper discuss the effect of the wave parameters on safety factors of submarine slope subjected to two wave pressure (linear wave pressure> second-order stokes wave pressure). The parametric studies show that the shallower of depth or the larger of wave length and wave height, the unlinear wave has more remarkable effect on the safety factors.4. Considering the soil disturbance, the disturbance degree is difined according to the undrainage strength and sensitivity of soil. Using the the upper bound approach of limit analysis, the stability of disturbed submarine slopes with different sensitivity are analyzed. The analysis results show that the higher sensitivity of soil, the more remarkable effect on the stability of submarine slope by the construction disturbance5. Considering the heterogeneity of soil strength, the critical equation of submairine slope is established based on the upper bound theorem. Meanmile, the safety factors is solved by using the optimization method combined with the strength reduction technique. Furthermoer, the correctness of the method is verified by calculating and analyzing the stability of typical example.6. The upper bound approach of limit analysis is extend to the stability analysis of multilayer submarine slopes under wave loading, and which is applied to the actual project. The analytical experssion of the rate of external work and internal energy dissipation are derived for multilayer seabed slopes incorporating a combining log-spiral rotational failure mechanism. with the numerical integration techniques and strength reduction technique, the stability of multilayer submarine slopes is analyzed. On the bisis, considering the wave loading, the stability of submarine slopes under linear wave or secend-order stokes wave are carried out. Through comparative analysis of typical examples, the validity of method is illustrated. Finally, the stability of actual slope lied in MADE KYUN delta is analyzed with the above method.