Experimental Research On Liquefaction Characteristics Of Seabed Gassy Sand Under Cyclic Loading

Shallow gas is one of the most important marine engineering geological disasters,which can cause serious damage to the marine engineering such as well drilling,petroleum platform,submarine cable,oil pipeline and so on.The existence of gas changes the mechanical properties of marine sediments.And many design and construction process of marine engineering have to consider the impact of submarine shallow gas.The marine gassy sediments are widely distributed in the offshore,lake,continental shelf and deep sea.It is a kind of special unsaturated soil with high saturation.In the marine environment,the wave load may induce liquefaction of the seabed and thus pose a threat to the safety of the buildings and structures on the seabed.But in the past,the study of liquefaction is mainly concentrated in saturated sand,there is little report on the liquefaction response characteristics of marine gassy sandy sediments.At present,China is speeding up the exploration and development of marine resources.Investigating the liquefaction response characteristics of seabed gassy sediment under wave loading can further enhance the cognition level of marine engineering geological disaster and provide a reference for the survey and design of marine engineering,which has important significance.This paper takes submarine shallow gas engineering geological disaster as the background which widely existed in the Hangzhou Bay east of China and the East China Sea,takes fine sandy soil of Hangzhou Bay seabed as the research object,by means of high pressure gas dissolving saturation instrument invented by Institute of Rock and Soil Mechanics,Chinese Academy of sciences,based on GDS dynamic triaxial test system and GCTS hollow cylinder apparatus,remodels and prepares gassy sand specimens with different initial gas content,carries out the study of liquefaction response characteristics of seabed gassy sand under cyclic(wave)loading.The main contents are as follows:1.To make the study more practical,studied north hydrogeological conditions of the East China Sea,analyzed the applicable range of wave theory and given the formula of wave load in the north of the East China Sea.2.To investigate the effect of initial gas content and dynamic load amplitude on liquefaction properties of gassy sand,exerted cyclic load with different amplitude on high saturation gassy sand with different gas content,studied the influence of saturation and dynamic load amplitude to dynamic strain and dynamic pore water pressure,dynamic strength and liquefaction of sand,analyzed liquefaction response characteristics of gassy sandy sediments,proposed a kind of pore water pressure growth model of gassy sand,obtained the dynamic strength curve of gassy sand under cyclic loading.3.To consider effect of continuous rotation of principal stress axis to liquefaction response characteristics of seabed gassy sand under the wave load,exerted wave load with different amplitude on gassy sand with different gas content,in the condition of continuous rotation of principal stress axis,carried out axial and torsional coupling shear test to research the dynamic strain,dynamic pore water pressure,dynamic strength and liquefaction response characteristics of gassy sand under the condition of continuous rotation of principal stress axis and analyzed the influence of continuous rotation of principal stress axis on the dynamic strength of sandy sediments.