饱和兰州黄土液化过程中孔压和应变发展的试验研究

Experimental study of development of strain and pore water pressure during liquefaction of saturated Lanzhou loess

采用WF12440型空心圆柱扭剪仪,用反压饱和法对初始饱和度较低的原状黄土进行饱和,进行室内原状黄土饱和液化试验研究,探讨了饱和兰州黄土液化过程中孔隙水压力、轴向应变、应力-应变滞回圈的发展规律。结果表明,对初始饱和度较低的原状黄土,反压饱和法使孔压系数B值达到0.95以上,即土样完全饱和;兰州黄土在均压固结条件下液化的孔压发展,开始时上升速率较缓慢,循环数一定后会出现孔压迅速增高的现象直至达到有效围压;应力-应变滞回特性随着振动次数的增加发生变化,塑性逐步增大;当轴向应变小于2%时,孔压增长缓慢;此后,孔压上升速率加大,3%应变可以出现在初始液化前;接近液化时偏应力为负值时的有效应力大于正值时的有效应力。

Using a dynamic hollow cylinder apparatus WF12440 as the test platform,this paper firstly studied the loess saturation by the back pressure method.The developments of pore water pressure,axial strain,deviatoric stress-axial strain curve during liquefaction are then investigated.Testing results indicate that the back pressure method can be successfully used for loess saturation;and the pore water pressure coefficient could achieve 0.95 and more.Under the condition of isotropic consolidation,pore water pressure increased slowly at the beginning;after several cycles the pore water pressure increased rapidly until it reached the effective consolidation pressure.The deviatoric stress-axial strain curve developed with the increase of cycles;and plastic strain increased step by step.When the axial strain was less than 2%,the pore water pressure increased slowly;afterwards,its increase ratio was much larger,and a strain of 3% could appear at the initial liquefaction process.Before liquefaction of the loess,the mean effective stress under negative deviatoric stress is larger than that under the positive deviatoric stress.