黄土各向异性强度特性的真三轴试验研究

黄土水平面内沉积结构及其发育的竖向裂隙构造使其具有明显的各向异性特征。通过黄土竖直裂隙向及其正交方向作用三维主应力状态几何空间八面体平面上3个空间域的真三轴试验,揭示了各空间域不同中主应力比值应力路径的剪切应力应变变化规律及抗剪强度变化规律。表明黄土竖向裂隙向作用大主应力的抗剪应力均大于水平面内正交两向作用大主应力的抗剪应力;中主应力增强作用能够诱导黄土的各向异性结构性;横观各向同性或者各向异性黄土八面体面上的强度破坏面随着平均球应力增大均呈椭圆、圆和曲边三角形变化,椭圆形破坏面可分别由轴对称压缩空间滑动面强度准则或轴对称挤伸空间滑动面强度准则近似地描述。

True triaxial tests on anisotropic strength characteristics of loess

The structure of loess consisting of horizontally deposited planes and vertically extended micro-fractures makes the anisotropic strength behavior of loess remarkable. Through triaxial tests, three principal stresses are alternatively loaded on loess specimens along the direction of vertical micro-fracture and two orthogonal directions in horizontally deposited plane, whose stress conditions are respectively corresponding to three sectors in the octahedral plane of geometric space. The experimental results reveal the laws of shear stress-strain and strength under different stress paths that the shear stress when the major principal stress is applied in the direction of vertical fracture is commonly larger than one during the major principal stress is loaded in the two orthogonal directions; the larger intermediate principal stress can induce more significant anisotropic structure of loess; the yield loci in the octahedral plane for cross-isotropic or cross-anisotropic loess appear to be elliptical, circular and triangular with curved edges changing with the increase of spherical stress, and elliptical yield locus can be approximatively expressed by the strength criterion of AC-SMP or AE-SMP.