原状黄土剪缩性测试与理论分析

 为揭示剪切过程中黄土的应力–剪缩规律，在黑方台典型滑坡后壁获取原状试样，开展了饱和黄土的等压固结不排水试验、等压固结排水试验，与非饱和黄土的常含水率试验，探讨了该黄土的应力应变规律和临界状态强度，调查了该黄土的状态参数与剪缩/剪胀行为，并进一步结合经典剪胀方程进行了对比研究。研究结果表明：首先，该饱和黄土在上覆荷载应力范围以内的临界状态线可近似为一条直线，在94～100 kPa基质吸力条件下非饱和黄土的临界状态线也可简化为一条与前者平行的直线；其次，该黄土总体表现为剪缩趋势或剪缩变形，但是受初始孔隙比、初始应力水平影响，该黄土可能表现出剪胀行为；第三，该原状土可用土的状态参数描述，且亦可表现出剪缩–剪胀的相转化行为；第四，剑桥模型的剪胀方程总体上能够反映该黄土的剪缩行为。

TESTING AND THEORETICAL ANALYSES ON THE CONTRACTIVE BEHAVIOR OF UNDISTURBED LOESS

To reveal the stress-contraction pattern of loess in shearing，undisturbed specimens were obtained from the backwall of a typical landslide in Heifangtai. Three series of triaxial tests were carried out，including isotropically consolidated undrained tests and isotropically consolidated drained tests for saturated loess，and constant water content tests for unsaturated loess. The stress-strain relationship and the critical state strength of the loess are explored. The state parameter and the contractive/dilative behavior of the loess are investigated. The stress-contraction/dilation rules of the loess are studied based on classical dilatancy equations. The findings are as below： firstly，the saturated soil shows a unique critical state line which could represent the major stress level corresponding to the thickness of Heifangtai loess，while the unsaturated soil at 94 to 100 kPa suction shows a roughly parallel critical state line. Secondly，the loess commonly demonstrates a tendency of contraction or contractive deformation， but can also shows a tendency of dilation or dilative deformation which is affected by its initial void ratio and intial stress level. Thirdly，the undisturbed loess can be depicted by the soil state parameter，and can also demonstrate the phase transformation behavior from contraction to dilation. Fourthly，the contractive behavior of the loess can be generally reflected by the dilatancy equation in the Cam-clay model.