原状黄土各向异性及卸载变形特征试验研究

Experimental Study on the Anisotropy and Unloading Deformation Characteristics of Intact Loess

为揭示原状黄土的各向异性和卸载变形特征，从水平和竖向2个方向取样，通过湿陷性试验、压缩试验、直接剪切试验、三轴剪切试验和卸荷三轴试验，对郑西客运专线贺家庄隧道出口洞顶Q3黄土进行黄土各向异性及卸载变形特征试验研究。结果表明：黄土的竖向和水平方向力学指标有明显差异，竖向和水平方向的压缩模量E3～2平均值分别为5．82和6．83MPa；黄土竖向湿陷性系数平均值为0．026，明显大于水平湿陷性系数平均值0．019；抗剪强度参数中水平向黏聚力大于竖向黏聚力，内摩擦角变化不大；黄土的卸荷变形与主应力差呈线性变化规律，当主应力差减小至O～90kPa时，迅速发生破坏，破坏时应变为0．5％～3．5％；原状黄土的破坏具有突变性，主要表现在卸荷破坏变形很小，破坏变形时间短，速度快。

To investigate the anisotropy and the unloading deformation characteristics of intact loess, a se- ries of laboratory tests, including collapsibility test, compression test, direct shear test, triaxial shear test and unloading triaxial compression test, were carried out, in which the Q3 loess was sampled from the level and vertical directions at the roof in Hejiazhuang tunnel exit of Zhengzhou-Xi＇an passenger dedicated line. The results show that there is significant difference between the vertical and level mechanical properties of loess. The average value of the level and vertical compression modulus E1-2 is 6.83 and 5.82 MPa respec- tively. The average value of vertical collapsibility coefficient is 0. 026, which is obviously greater than the lateral one with the value of 0.019. For the parameters of shear strength, the lateral cohesion is greater than the vertical one, the internal friction angle varies little. The unloading deformation of loess changes linearly with the principal stress difference. Failure will occur rapidly when the principal stress difference is reduced to 0 ~ 90 kPa with the strain between 0.5% ~ 3.5%. The failure of the intact loess has mutagenicity due to small unloading deformation, short failure time and quick failure speed.