Effects of variable shear rate on residual strength of expansive soils and its engineering enlightenment
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摘要: 残余强度对滑坡的变形、稳定性具有重要影响，滑坡运动全过程中往往涉及到变速率问题，具体表现为加速率和减速率作用。为研究膨胀土残余强度的加速率和减速率效应，开展了一系列变速率环剪试验，分析了膨胀土残余强度在不同加速率和减速率条件下的变化规律，并讨论了残余强度的加速率和减速率效应在滑坡不同变形发展阶段中起的作用。结果表明：加速率和减速率均对残余强度具有强化作用（正作用），加速率对残余强度的强化作用比减速率的更显著，在较大法向应力条件下残余强度的加速率和减速率效应更显著。残余强度的加速率和减速率效应是剪切速率变化导致剪切面状态变化的结果，剪切面上土颗粒在变速率条件下须重新调整以适应新的剪切速率条件，从而导致了残余强度变化。在滑坡运动全过程当中，残余强度的加速率和减速率效应对滑坡向减速堆积状态演化有利。Abstract: The residual strength has a key impact on the deformation and stability of landslides. The whole process of landslide movement often involves the phenomenon of variable shear rates, which is manifested by the acceleration rate and deceleration rate. In order to investigate the effects of the acceleration and deceleration rates on the residual strength of expansive soils, a series of ring shear tests with variable shear rates are conducted to analyze the variation rules of residual strength of expansive soils under different acceleration and deceleration rates, and the role of the effects of the acceleration and deceleration rates of the residual strength at different deformation stages of landslides is discussed. The results show that both the acceleration rate and the deceleration rate have a strengthening effect on the residual strength (positive effects), and the strengthening effects of the acceleration rate on the residual strength are more significant than those of the deceleration rate. The effects of the acceleration and deceleration rates on the residual strength are more significant under the larger normal stress conditions. The effects of the acceleration and deceleration rates on the residual strength are considered to be the result of changes in the state of the shear plane caused by changes of the shear rate, and the soil particles in the shear plane must be readjusted to adapt to the new shear rate conditions under variable shear rate conditions, resulting in changes in the residual strength. During the whole process of landslide movement, the effects of the acceleration and deceleration rates on the residual strength are beneficial for the evolution of landslides towards a deceleration accumulation state.
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Keywords:
- expansive soil /
- residual strength /
- rate effect /
- ring shear test /
- landslide
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图 2 加速率和减速率环剪试验方案
Figure 2. Ring shear test schemes with different acceleration and deceleration rates
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图 3 不同加速率和减速率条件下膨胀土环剪试验结果
Figure 3. Ring shear test results of expansive soils under different acceleration and deceleration rates
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图 4 不同加速率和减速率条件下膨胀土的残余强度比
Figure 4. Residual strength ratios of expansive soils under different acceleration and deceleration rates
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图 5 不同剪切速率下膨胀土平均残余强度比
Figure 5. Average residual strength ratios of expansive soils under different shear rates
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图 6 膨胀土剪切面微观结构特征
Figure 6. Microstructural characteristics of shear zone of expansive soils
表 1 试验膨胀土基本物性参数
Table 1 Basic physical parameters of test expansive soils
天然密度ρ/(g·cm-3) 相对质量密度Gs 天然含水率w /% 液限wL/% 塑限wP/% 塑性指数IP 液性指数IL 自由膨胀率δef /% 1.97 2.73 26.06 47.3 22.1 25.2 0.12 50 
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