非饱和原状黄土的变形及屈服特性试验研究

对不同吸力非饱和原状黄土进行了等应力比三轴压缩及常规三轴剪切路径下的试验,研究了偏应力比q/p(q及p分别为净平均应力及偏应力),吸力及净围压对不同应力路径下变形及屈服特性的影响。研究结果表明:在等应力比三轴压缩及常规三轴剪切过程中,孔隙比e与净平均应力p关系(e-lnp)皆位于二条相交的直线上,吸力、偏应力比及净围压对弹性指数的影响很小,对屈服应力及压缩指数的影响较大。等应力比三轴压缩路径下,偏应力比一定时,屈服应力及压缩指数皆随吸力的增大而增大;吸力一定时,随偏应力比的增大而先增大后减小。常规三轴剪切路径下,吸力一定时,屈服应力及压缩指数皆随净围压的增大而增大;净围压一定时,随吸力的增大,屈服应力增大,压缩指数减小。以塑性体应变作为硬化参数时,q-p平面上的初始及后继屈服面皆为对称于饱和土K₀线的倾斜椭圆,吸力及应力增大时,屈服面没有旋转,而是产生等向扩大。

Experimental Study on Deformation and Yielding Characteristics for Unsaturated Intact Loess

A series of triaxial tests under different stress paths were performed on intact loess with different suctions, including constant stress ratio triaxial compression and conventional triaxial shear. The influences of suction, deviatoric stress ratio (q/p, q, p are respectively net mean stress and deviatoric stress) and net confining pressure on the deformation and yielding under different stress paths were investigated. The results showed that during constant stress ratio triaxial compression and conventional triaxial shear, the data of void ratio (also called e) versus the net mean stress (e-lnp) were lies on the two intersecting lines. The suction and deviatoric tress ratio as well as net confining pressure had little influence on the elastic index, but large influence on the yield stress and compression index. Under constant stress ratio triaxial compression stress path, the yield stress and the compression index increased consistently with suction for a certain stress ratio, and firstly increased and then decreased with the increase of deviatorics tress ratio for a certain suction. Under conventional triaxial shear stress path, the yield stresses and the compression index increased with net confining pressures for a certain suction, and decreased with the increase of suction for a certain net confining pressures. Using plastic volumetric strain as the hardening parameter, the shapes of the initial and subsequent yield curves on the q-p plane were near skewed ellipses centered on K_0w line of the saturated soil. The isotropic expansion of the yielding curves occurred with the increase of the suction or stress, without any rotation of the axis.