K_0预固结对非饱和重塑黄土强度与变形特性影响的研究

为了探讨K_0预固结对土的强度及变形特性的影响,用改进的非饱和土三轴仪对重塑Q3黄土做了两组共36个试验。第一组共24个试验,每个试验包括三个阶段,即试样先在竖向压力为常数的条件下K_0预固结,再经过控制吸力和净围压为常数的各向等压固结,最后进行控制吸力和净围压为常数的排水剪切试验;第二组共12个试验,每个试验仅包括第一组试验的后两个阶段。试验结果表明:第一组试验应力–应变曲线的初始切线斜率大于第二组试验的初始切线斜率,且吸力越大、净围压越大,差距越明显;第一组试验的破坏应力均明显大于第二组试验的破坏应力,但除了吸力为0 kPa的饱和试样外,两组试验相应的体应变相差不大;第一组试验剪切初始阶段有轻微的剪胀现象,但并不明显,并很快转变为剪缩,第二组试验各试样均处于剪缩状态;虽然两种试验条件下有效摩擦角及破坏比相差不大,但邓肯–张模型的初始模量表达式的指数n相差很大,且总凝聚力–吸力曲线及邓肯–张模型的初始模量表达式的系数与吸力的关系曲线(即k–s曲线)结果相差也较大。基于试验研究结果,提出了考虑K_0预固结、吸力和净围压三者综合影响的表观凝聚力、切线杨氏模量的修正计算公式,完善了非饱和土的增量非线性模型。

Deformation and strength properties of unsaturated remolded loess under K0 pre-consolidation condition

In order to discuss the influence of K₀ pre-consolidation on the strength and deformation properties of loess, the experiments on a total of 36 remolded Q₃ loess samples in two groups are carried out using the improvement of unsaturated soil triaxial apparatus. The first group includes 24 tests, and each test includes three stages, namely, the samples are consolidated under the constant vertical pressure, and then, they are consolidated through the constant control suction and net confining pressure, and the drainage shear tests with constant control suction and net confining pressure are carried out in the end. The second group includes 12 tests, but each test only includes the last two stages of the first group. The results show that the initial tangent slope of stress-strain curves of the tests in the first group is greater than that of the second group, and the difference becomes more and more obvious with the increase of the suction and net confining pressure. The failure stress of the test samples in the first group is significantly greater than that of the second group. Except the tests on the saturated samples with no suction, the volumetric strain of two groups is similar. Unlike the shear shrinkage state of the test samples in the second group, the test samples of the first group exhibit slightly shear dilatancy at the initial stage, but it is not obvious and they become shear shrinkage insantly. Although the effective internal friction angle and destruction ratioare almost the same under the two kinds of experimental conditions, n is fairly different. Besides, the curves of total cohesion-suction and the relation curves of the index k in the initial modulus expression of Duncan-Chang model and suction (k-s) are rather different. Based on the test results, the modified formulas of apparent cohesion and tangent Young's modulus are put forward considering the comprehensive effects of