循环荷载下人工结构性土变形与强度特性试验研究

Experimental study of behavior of deformation and strength of artificial structural soft clay under cyclic loading

针对长期动载作用下天然沉积结构性黏土地基强度和刚度循环软化问题,分别以水泥和食糖为模拟粒间胶结和大孔隙的材料,制备了不同胶结强度和初始孔隙比的人工结构性土,开展了人工结构性土与相应重塑土的动三轴试验,分析了土体胶结强度、初始孔隙比、围压和动应力幅值对累积变形和动强度的影响规律。试验结果表明:累积应变-振动次数曲线以临界循环应力为界分为:塑性安定型、临界型和破坏型;临界循环应力随胶结强度增大、初始孔隙比减小而增大;土体胶结强度越高,脆性破坏越明显,累积应变曲线转折点对应的应变越小。动强度的应变破坏标准采用转折点应变值更符合土性变化规律;动强度随胶结强度增大、初始孔隙比减小而增大;动黏聚力cd随破坏振次增大而降低,而动内摩擦角φd基本不变。试验结果可为软弱土地基动力灾变控制提供有益参考。

This paper aims at studying the cyclic softening of strength and stiffness of natural sedimentary structural clay in long-term dynamic loading. The artificial structured soils with different inter-particle bonding strengths and different initial void ratios are prepared, using cement as bonding material and sugar to mimic the large pores. A series of dynamic triaxial tests is performed on the structured clay and corresponding remolded soil to investigate the influence of bonding strength, initial void ratio, confining pressure and dynamic stress amplitude on the accumulated deformation and dynamic strength. Three distinct relationships between accumulative plastic strain and cyclic number can be identified according to the critical cyclic stress ratio（CSR）： plastically stable, critical and destructive types. The critical cyclic stress increases with the increase of inter-particle bonding and the decrease of initial void ratio. The structured clay with higher bonding strength behaves in more obvious brittle failure, and has a smaller strain associated with the inflection point of the accumulated strain curve, which is suitable to be regarded as the strain failure criteria for dynamic strength. Moreover, the dynamic strength increases with the increase of inter-particle bonding and the decrease of initial void ratio, and the dynamic cohesion Cd decreases with the increment of cyclic failure number; while the dynamic angle of internal friction φd basically remains unchanged. This study results can provide useful reference for controlling the dynamic catastrophes of soft ground.