Behaviour of coarse grained soil with rotation path of stress Lode’s angle
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摘要: 为研究应力空间中恒定的平均应力和偏应力条件下粗粒土的力学行为,采用自主研发的微摩阻大型真三轴仪,在同一个偏平面的多级偏应力条件下开展了三组旋转应力路径试验。试验过程中,调整应力洛德角在-30°~30°之间增减循环2次,覆盖了偏应力平面1/6范围,并由对称性而代表整个偏应力平面。在不同的应力比条件下,结合应力路径分析了体积应变、偏应变、应变洛德角与应变路径的演化规律。试验结果表明：首先,在恒定球应力与偏应力条件下,受应力洛德角影响,土体仍会发生明显变形。在应力洛德角的初次增加过程,土体发生弹塑性变形,随后的过程中,土体的偏应变、体积应变与应变洛德角均表现出滞回性。第二,在恒定的球应力与偏应力下,初始偏应变的斜率仍然随着偏应力的增加而增加。第三,随着应力洛德角变化,受初始应力比影响,土体可能从初始的稳定状态达到变形破坏状态。最后,提出了土的本构模型中需补充考虑的应变洛德角关系式。Abstract: In this study, the behaviour of coarse grained soil following the rotation path of stress Lode’s angle is studied under the constant mean stress p and the constant deviatoric stress q in stress space. A large-scale true triaxial apparatus with special friction-reduction technique is used to conduct rotation stress path tests in the deviatoric plane. In each test, the stress Lode’s angle is increased and then decreased between -30° and 30° twice, which covers one-sixth deviatoric plane and represents the whole deviatoric plane due to its symmetry. Under different stress ratios, the volumetric strain, deviatoric strain, strain Lode’s angle and strain path are analyzed together with the rotation stress path. The conclusions are drawn as follows: firstly, soil deforms together with the variation of stress Lode’s angle under the constant mean stress and deviator stress. In the first increasing process of stress Lode’s angle both the elastic and the plastic strains occur. In the following processes, hysteresis can be observed for the deviator strain, volumetric strain, and strain Lode’s angle, the last of which necessarily determines a certain point in strain space. Secondly, the slope of the initial deviatoric strain still increases with the deviatoric stress following the current stress paths. Thirdly, the soil can achieve failure with the increasing stress Lode’s angle, which is affected by the initial stress ratio. Finally, an equation reflecting the variation of strain Lode’s angle is proposed, which should be included in the constitutive model for soil.
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Keywords:
- true triaxial test /
- Lode’s angle /
- rotation stress path /
- deviatoric plane /
- coarse grained soil
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图 1 长江科学院大型真三轴仪(a)和真三轴试样(b)
Figure 1. Large-scale true triaxial apparatusin CRSRI (a) and its specimen (b)
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图 3 等p等q试验在偏平面上的路径（p=0.4 MPa）
Figure 3. Paths in deviatoric plane (p=0.4 MPa) in constant p and q tests
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图 4 3个主应力的控制值与计算值对比
Figure 4. Comparison between controlled and calculated values of three principal stresses
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图 7 应变洛德角随应力洛德角的变化曲线
Figure 7. Variation of strain Lode’s angle with stress Lode’s angle
表 1 真三轴试验方案
Table 1 Schemes of true triaxial tests
编号 p/MPa q/MPa b θσ/(°) 循环次数 CPQ1 0.4 0.4 0~1 -30°~30° 增减2次 CPQ 2 0.4 0.5 0~1 -30°~30° 增减2次 CPQ 3 0.4 0.6 0~1 -30°~30° 增减2次 
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