Q3砂黄土真三轴强度变形特性研究

为了研究Q3砂黄土强度变形特性，以甘肃永靖黑方台Q3砂黄土为研究对象，利用西安理工大学研制的真三轴仪，进行了3个围压（50、100 kPa 和200 kPa）、3个b值（0、0.25和0.5）和3个含水率（5%、10%和15%）不同工况试样破坏情况的真三轴试验。试验结果发现：（1）真三轴条件下Q3砂黄土剪切破坏方式以侧胀破坏、单缝剪切破坏为主，其次少数土样发生锥形破坏、双缝剪切破坏和T型缝剪切破坏。（2）相同围压和含水率、不同中主应力比（b）的情况下，Q3砂黄土的主应力差随中主应力比增大而增大，应力-应变关系曲线为强硬化型，剪胀现象明显；中主应力比对广义剪应力和广义剪应变之间关系有一定影响，随b值增加，曲线依次增加；随b值的增加，强度降低，广义剪应力与平均球应力比（q/p）与主应变关系曲线逐渐变缓，且曲线依次降低。（3）随含水率增加，Q3砂黄土由固态向半固态转化过程中，不同中主应力比时黏聚力均出现明显降低，但内摩擦角则出现微小增加。

Strength and deformation characteristics of Q3 sand loess under true triaxial condition

In order to study the strength and deformation characteristics of Q3 sand loess from Heifangtai, Yongjing, Gansu province, using the true triaxial apparatus developed by Xi'an University of Technology, true triaxial tests are carried out under conditions of different confining pressures (50, 100, 200 kPa), ratios of intermediate principal stress (b =0, 0.25 and 0.5) and water contents (5%, 10% and 15%). The test results illustrate that: (1) The shear failure modes of Q3 sand loess are displayed by lateral bulge failure and monolete shear failure under the true triaxial conditions; and there are other modes for few soil samples including taper failure, double-slit shear failure and T-shape shear failure. (2) The deviatoric stress difference of Q3 sandy loess increases with the ratio of intermediate principal stress when the confining pressure and moisture content are the same, while the ratio of intermediate principal stress (b) is different. Meanwhile, the stress-strain relationship curve shows hardening and obvious shear dilatancy phenomenon. However, the ratio of intermediate principal stress effects the relationship between generalized shear stress and generalized shear strain; the relation curve increases accordingly with the increase of b. With the increase of b, the strength decreases; and the relation curve between the generalized shear stress and the average spheric stress ratio (p/q) becomes flat gradually, and decreases accordingly. (3) With the increasing of water content, the Q3 sandy loess transfers to semisolid state from initial solid state. The cohesions with different ratios of intermediate principal stress all declines remarkably; but the internal friction angle increases a little.