Experimental study on damping ratio of overconsolidated clay under different cyclic confining pressures
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摘要: 通常采用单一轴向循环荷载模拟交通荷载，然而，真实的交通荷载引起的应力场包含循环变化的轴向偏应力和围压。除此之外，部分下卧软黏土是超固结土，并非正常固结土，且针对交通荷载作用下软黏土的阻尼比变化规律鲜有研究。因此，通过对超固结软黏土开展一系列变围压不排水循环加载试验，对超固结软黏土在变围压循环荷载作用下的阻尼比变化规律进行了研究，分析了超固结比和循环围压对阻尼比的影响。研究结果表明：变围压循环荷载作用下，不同试验条件对应的归一化阻尼比与累积塑性应变关系曲线相似，且归一化阻尼比随累积塑性应变的增长逐渐减小。超固结比和循环围压对阻尼比的衰减程度影响显著，阻尼比随超固结比和循环围压的增大而减小。基于上述试验结果，建立了一个能反映阻尼比随累积塑性应变变化规律的计算模型。上述研究成果可加深对超固结土在动荷载下阻尼比变化规律的认识，从而为交通荷载作用下的土体动力反应分析提供试验基础。Abstract: Traffic loading is usually simulated by single cyclic deviator stress. However, the vertical normal stress and horizontal stress acting on the soil elements are all varied cyclically under the traffic loading. Nevertheless, part of the subgrade soil is overconsolidated, rather than normally-consolidated. There are few researches on the development of damping ratio of soft clay under the traffic loading. Hence, a series of cyclic triaxial tests with cyclic confining pressure are conducted on the overconsolidated clay under undrained conditions, and the effects of cyclic confining pressures and overconsolidated ratios on the development of damping ratio are investigated. It is observed that the relationship between the normalized damping ratio and the cumulative axial strain are similar under different test conditions, in which the normalized damping ratio degrades with the increasing cumulative axial strain. Besides that, the overconsolidated ratios and cyclic confining pressures have significant effects on the development of damping ratio: the damping ratio decreases with the increase of the overconsolidated ratio and cyclic confining pressure. Based on that, an empirical formula as a function of the cyclic confining pressure and overconsolidated ratio is proposed to predict the damping ratio. The above results can deepen the understanding of damping ratio of the overconsolidated soft clay under the traffic loading, and provide experimental basis for the dynamic analysis of soils under the traffic loading.
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图 1 不同循环围压下归一化阻尼比随累积塑性应变变化曲线
Figure 1. Relationship between normalized damping ratio and cumulative axial strain under different cyclic confining pressures
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图 4 拟合和实测的DN–εp曲线对比
Figure 4. Comparison between measured and predicted curves of DN–εp
表 1 循环三轴试验方案
Table 1 Programs of cyclic triaxial tests
编号 OCR CSR qampl/kPa σampl3/kPa η C01 1 0.35 35 24 1.00 C02 2 0.35 35 24 1.00 C03 4 0.35 35 25 1.00 C04 8 0.35 35 24 1.00 C05 4 0.35 35 0 0.33 C06 4 0.35 35 41 1.50 Y01 8 0.35 35 0 0.33 Y02 2 0.35 35 41 1.50 Y03 8 0.35 35 41 1.50 Y04 2 0.35 35 0 0.33 
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