Cyclic triaxial tests were performed on marine sandy soil from Zhoushan Seas by GDS loading apparatus under different exciting amplitudes of bidirectional wave loadings to study the liquefaction of typical marine soil samples MS1 and MS2,which are taken from Wushitang coast and Dongsha coast respectively. X-ray diffraction(XRD) and scanning electron microscope(SEM) experiments were accomplished to study the phase structures of MS1 and MS2. MS1 and MS2 are both alkaline marine sediments with quartz mineralography. It is found that the high-cycle liquefaction on marine coarse sand MS1 can be induced under low amplitude and its low-cycle liquefaction can be induced under high amplitude. The marine fine sand MS2 can carry high-cycle wave loading under low liquefying deviatoric stress and can carry only low-cycle wave loading under high liquefying deviatoric stress. The liquefaction pore pressure model and its controlling parameters′values are established based on the normalized relationship between cycle-time at any time during initial liquefying period and initial-liquefaction critical cycle-time. The typical marine sandy samples MS1 and MS2 are inclined to be liquefied under the accumulation of exciting stress ratio. The endochronic failure model under initial-liquefaction and its controlling parameters′ values are obtained based on dynamically incremental pore-pressure ratio and damage parameter introduced by Finn. It is found that the liquefying failure of MS1 is induced by shear-contraction due to excessively exciting compression strain;and marine fine sand MS2 is liquefied under cumulative tension strain that causes the contacts failure of soil particles. The cumulative deterioration for micro-meso-physical structures of marine sediments induces their macro initial-liquefaction failure. The macro-mechanical characteristics of marine sandy soil from Zhoushan Seas consist with their micro-meso-physical phase structures evolution.% 为探究舟山海相土在海洋环境中的液化失效规律,选用2类代表性海相砂土：乌石塘海相粗砂MS1及东沙海相细砂MS2,利用X射线衍射(XRD)及扫描电镜(SEM)试验获得微细观物相结构,二者均属石英矿相碱性海相沉积物。在不同激振幅值下,采用GDS动三轴系统进行一系列双向循环激振加载试验。试验结果表明：海相粗砂MS1产生高周循环液化时对应的激振幅值较低,而在低周液化下激振幅值则较高,海相细砂 MS2在液化偏应力较小时可承受高周循环加载,而在液化偏应力较大时只可承受低周循环。基于归一化初始液化周数比建立舟山海相砂土的液化孔压模型并给出参数取值,模型揭示：2类海相砂土均随激振应力比增加而更易于液化；基于循环增量孔压比及Finn破损参数,建立舟山海相砂土初始液化破坏内时模型,并给出试验参数,模型揭示：过大的激振压缩应变诱发剪缩变形,导致海相粗砂MS1液化破坏,而海相细砂MS2的液化破坏则源于拉应变增大诱发的颗粒间接触失效。海相砂土宏观尺度的初始液化破坏是其微细观物相结构劣化积聚的最终结果,宏观力学机制与微细观试验分析结论吻合。
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