Evaluation Of Seismic Stability Of Submarine Clay Slopes Based On Upper Bound Approach Of Limit Analysis

Marine geological environment is complex and natural disasters occur frequently,among which submarine landslides are the most dangerous ones.Submarine landslides can directly destroy infrastructure such as offshore oil and gas platforms and submarine cables,causing huge losses in human life and property.The earthquake is the main factor that triggers the instability of the submarine slope.Therefore,the study of the seismic stability of the submarine slope has become a hot issue in the current marine geotechnical engineering.This article is based on the limit analysis method,consider the horizontal and vertical seismic loads,the upper limit of the seismic stability of the submarine and non-homogeneous clay slopes is analyzed.Based on the upper limit method of limit analysis,a rapid assessment method for seismic slip of submarine slope is proposed.In addition,considering the heterogeneity of seismic load and soil strength,the local sliding mechanism of the layered clay slope was further discussed.The specific research content is as follows:1.Taking the submarine layered slope as the research object,based on the logarithmic spiral destruction mechanism and the rectangular coordinate modeling method,the expressions of the gravitational power and the internal energy dissipation rate of the layered slope are deduced.Combined with the optimization method and strength reduction technology,the safety factor and critical slip surface of the submarine layered slope are solved,and examples are given to verify the effectiveness of the proposed method.2.The destruction mechanism with weak interlayer slope is improved,and a logarithmic spiral-linear composite destruction mechanism is proposed.The external force power and internal energy dissipation rate under the destruction mechanism were deduced,and the upper limit analysis of the stability of the seafloor slope with weak interlayer was realized,and a typical example verifies the rationality of the new destruction mechanism.3.Considering the pseudo-static seismic load and its effect on pore water,based on the limit analysis upper bound method,the power of the seismic force to the submarine slope is deduced,establish a critical state equation for the stability of submarine slopes under earthquakes.Combining numerical integration techniques and optimization methods to achieve safety factor and critical slip surface solution.On this basis,the effects of horizontal and vertical seismic forces on the submarine slope were discussed separately.The resultsshow that when the horizontal seismic acceleration is large,the influence of vertical seismic force becomes very significant,the influence of vertical seismic force must be considered.4.Taking the heterogeneous submarine slope with a linear increase in cohesion as the research object,the expression of the internal energy dissipation rate of an inhomogeneous slope is deduced.Established a critical state equation for the stability of submarine slopes under earthquakes.An analysis of the upper limit of seismic stability for heterogeneous submarine slopes.On this basis,an upper limit analysis was conducted on the typical heterogeneous submarine slope section near the Liwan 3-1 oil and gas field in the northern slope of the South China Sea.The comparison of calculation results shows that this method can better realize the seismic stability evaluation of the slope in this area.5.Based on the Newmark slider displacement method,the limit analysis upper bound method is used to solve the seismic yield acceleration of submarine slope.Combined with the empirical regression formula,the seismic slip amount can be quickly solved and the rapid assessment of the seismic hazard of the submarine slope can be realized.Analysis results of typical examples show that there are differences in different empirical regression formulas.In the future,the corresponding model should be established or modified for specific regions to improve the accuracy of calculation.6.Based on the upper limit method of limit analysis,the sliding surface searching method and failure mechanism are improved,and the local sliding upper limit analysis of multi-soil submarine slope and heterogeneous submarine slope is realized.For the combination of the upper soft under hard and the upper hard under soft,the combination of the two layers of the subsea slope and the non-homogeneous layered subsea slope,the overall and local stability of the slope under seismic conditions are studied,and the influence of the seismic load on the local sliding mechanism is further discussed.