Application Of Multivariate Compound Extreme Value Distribution Theory To The Wave-induced Seabed Liquefaction

Seabed liquefaction can bring adverse effect to coastal engineering structures, oreven cause structures damage and environmental pollution under extreme seaenvironment. Thus, the analysis of wave-induced seabed liquefaction has importantsignificance for ensuring the safety of marine engineering structures.It is necessary to comprehensively consider the dynamic load conditions, soilconditions and the initial stress conditions when judging the possibility of seabedliquefaction under wave action. Generally, the liquefaction can be accomplished whenextreme wave force acts on the seabed of which clay content is less than20%, relativewater content is equal to or greater than0.9, and buried depth is less than6m.The state equation of wave-induced seabed liquefaction is summarized, and therandom variables are analyzed. Results show that the distribution of the wave heightand wave length are both subject to Weibull distribution, the soil parameters obeynormal distrubution. The self-correlation of the soil parameters is important to study.The soil parameters data in the same depth is more uniform, therefore, thecharacteristics of soil can be represented by the statistical average in a certain area.Due to the relative distances of the different soil parameters in the same position areapproximate, it is feasible to comprehensively consider all the soil parameters.Based on the Multivariate Compound Extreme Value Distrubution Theory, a newprobability calculation method for seabed liquefaction under wave-induced cyclicloading is proposed. In the application, the probability of liquefaction is calculated byusing ISPUD software with the wave and soil properties taken into account. Theproposed method is applied to calculate the liquefaction probability of the river mouthdelta of Yellow River under8grade sea waves. The results are similar to theprobability of liquefaction which calculated by using first order second moment method.There are extreme wave-induced shear failure and liquefaction in seabed ofwhich relative water content is equal to or greater than0.9, liquidity index is greaterthan or equal to0.75, clay content is between3%and20%, cohesion is less than8kPa, and internal friction angle is less than11. It is possible to distinguish shearfailure and liquefaction using Multivariate Compound Extreme Value Distribution.When the shear failure probability is greater than the probability of liquefaction,seabed tends to shear fail under wave actions, on the contrary, seabed liquefies.