Study On Triggering Mechanism And Migration Characteristics Of Submarine Landslide Under Wave Load

With the implementation of the national strategy of "One Belt And One Road" and"Maritime Power",China's Marine infrastructure construction has entered a period of vigorous development.Submarine landslide is one of the geological disasters that threaten the safety construction and healthy operation of Marine infrastructure.It has the characteristics of wide coverage,large impact area and serious disaster consequences.Its triggering mechanism,action form and damage characteristics are extremely complex.Among them,the statistics of triggering factors of offshore submarine landslide show that,wave load is the key factor of landslide disaster.Therefore,it is of great theoretical significance and engineering value to carry out research on the triggering mechanism of offshore submarine landslide disaster under wave load.Based on the case of Zhujiajian submarine landslide,this paper studies the triggering mechanism and migration characteristics of submarine landslide under wave load by means of laboratory experiments,theoretical analysis,model tests,numerical simulation and other research methods,and obtains a series of research results as follows:(1)This paper investigates the research results of submarine landslide at home and abroad,especially analyzes a large number of submarine landslide cases at home and abroad,and summarizes the main disaster mode,inducing conditions and triggering mechanism of submarine landslide disaster.Targeted carried out in this paper,based on a project where zhujiajian pointed regional geological survey,zhujiajian pointed submarine landslide failure process are analyzed,studied the wave load form,the action of the submarine slope soil revealed based on the linear wave theory and limit equilibrium analysis method of zhujiajian pointed submarine landslide triggering mechanism of wave load,zhujiajian pointed submarine landslide belongs to liquefaction and shear failure under the action of coupling arc of oscillation caused by damage type underwater landslides.(2)For underwater landslides simulation test process is difficult to effective information acquisition,based on fiber Bragg grating sensing technology and fiber optical sensors numerical simulation optimization,put forward the suitable for offshore monitoring sensor technology parameters optimization of landslide model test method,developed with high sensitivity,strong corrosion resistance of the fiber Bragg grating sensor.Combined with the WDM technology of optical fiber sensing,a sensor WDM networking method in model test is established.It breaks through the problem of real-time acquisition of multiple information in the process of offshore submarine landslide disaster,and provides a method basis for on-site monitoring of offshore submarine landslide disaster.(3)For submarine landslide occurrence caused by environment,complex and difficult to live capture field test is difficult to carry out such issues,research and development of the offshore submarine landslide simulation test system,the precision of different types of wave load applied,eliminates the traditional test device exists rebound wave boundary effect,realized the accurate test boundary conditions applied.In addition,the developed optical fiber monitoring system realizes the real-time acquisition of multiple precursor information of offshore submarine landslide under wave load,and establishes a large physical simulation test platform that can simulate a variety of submarine landslide disasters.(4)Based on the field soil data and the similarity theory,similar materials with similar mechanical parameters to the field soil foundation were selected.By using the developed offshore submarine landslide simulation test system and the FBG monitoring system,the model test of offshore submarine landslide under different wave loads is carried out to realize the simulation of the whole process of offshore submarine landslide and obtain multiple precursor information of offshore submarine landslide.By observing the phenomenon in the process of offshore submarine landslide,the change of permeability temperature-pressure field,displacement field and velocity field characteristic,found the wave load caused by offshore submarine landslide under the control of the liquefaction and shear damage coupling effect,the wave action leads to offshore submarine slope internal pore water pressure,reduces the slope of the shear strength,and shear stress produced by the wave action to drive the occurrence of landslides.The failure of offshore submarine slope is the first at the foot of slope under the continuous action of wave load.Submarine landslide mainly occurs in the middle and below positions of offshore submarine slope.Wave loads on offshore submarine slope displacement and pore water pressure at the same time,the landslide displacement and pore water pressure are all appeared the phenomenon of mutation,but the pore water pressure mutation time earlier than the displacement mutation time about 5s,through time similar scale conversion 50:1 on-site prototype,the pore water pressure mutation time about submarine landslide early 30s.Therefore,in the field monitoring of submarine landslide,the pore water pressure can be considered as the evaluation index of the stability of submarine slope.(5)For offshore seabed under wave load of landslide disaster mechanism and evolution process problems,in order to further verify the theory and simulation test results,is established based on the theory of multiphase flow of two phase flow model,based on simulation experiment was carried out by offshore submarine landslide disaster evolution process simulation,to verify the submarine landslide disaster evolution process,explores the characteristics of offshore submarine slope under wave load migration.The results show that both wave period and wave height have influence on the disaster process and migration characteristics of offshore submarine landslide.With the increase of wave height,the time required for offshore submarine slope instability and failure lengthens,and the migration distance of landslide body increases.With the shortening of wave period,the process of instability and failure of offshore submarine slope is intensified,but the migration distance of the slope body is shortened.