Liquefaction of Unsaturated Sand Considering the Pore Air Pressure and Volume Compressibility of the Soil Particle Skeleton
Liquefaction of Unsaturated Sand Considering the Pore Air Pressure and Volume Compressibility of the Soil Particle Skeleton
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DOI：
10.3208/sandf.48.87
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发表时间：
2008-02
影响因子：
3.7
通讯作者：
T. Unno;M. Kazama;R. Uzuoka;Noriaki Sento
中科院分区：
文献类型：
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作者：
T. Unno;M. Kazama;R. Uzuoka;Noriaki Sento
为了更好地了解非饱和土的液化状态，进行了一系列非饱和土的动三轴试验。在不排水条件下，对干密度相同但初始吸力不同的细砂施加循环剪应变。在循环剪切过程中，连续测量了土颗粒骨架的体积变化、孔隙水压力和孔隙空气压力。使用Bishop定义的有效应力（Bishop等人，1963），其中净应力和吸力有助于有效应力，我们的试验结果表明，非饱和砂土试样与相当低的饱和度失去有效应力由于循环剪切。在零有效应力状态下，非饱和试样的行为类似于液体在很大程度上相同的饱和试样。从实验和理论考虑，零有效应力状态（即，当孔隙空气压力和水压力都增加到等于初始总压力的点时，发现已经建立了非饱和砂土的液化）。如果孔隙水的体积变化可以忽略不计，则不排水条件下孔隙空气的体积变化等于土壤颗粒骨架的体积变化。因此，非饱和土的液化一般取决于土颗粒骨架的体积压缩性和饱和度。另一方面，根据Boyle-Charles定律的理想气体方程，可以从初始孔隙空气压力（通常为大气压力）和最终孔隙空气压力（初始围压）计算出导致零有效应力状态所需的体积变化。因此，非饱和土的液化也取决于初始围压。基于这一概念，非饱和土的液化潜力可以通过比较土颗粒骨架的体积压缩性和导致零有效应力状态所需的孔隙空气的体积变化来评估。
A series of cyclic triaxial tests of unsaturated soils was conducted to get a better understanding of the general liquefaction state of unsaturated soils. In the tests, cyclic shear strain was applied to fine clean sand with the same dry density but different initial suction states under the undrained condition. During cyclic shear, the volume change of the soil particle skeleton, the pore air pressure and the pore water pressure were measured continuously. Having used the effective stress defined by Bishop (Bishop et al., 1963), where the net stress and suction contribute to the effective stress, our test results showed that unsaturated sand specimens with quite a low degree of saturation lose their effective stress due to cyclic shear. At a zero effective stress state, unsaturated specimens behaved similarly to liquids in much the same way as saturated specimens. From experimental and theoretical considerations, the zero effective stress state (i.e., liquefaction) for unsaturated sand was found to have been established when both the pore air and water pressures build up to the point where it is equal to the initial total pressure. A volume change of pore air under the undrained condition, if a volume change of pore water is negligible, is equal to that of the soil particle skeleton. Therefore, it can be concluded that the liquefaction of unsaturated soil generally depends on the volume compressibility of the soil particle skeleton and the degree of saturation. On the other hand, according to the ideal gas equation of Boyle-Charles law, the volume change required to bring about a zero effective stress state can be calculated from the initial pore air pressure (usually the atmospheric pressure) and the final pore air pressure (the initial confining pressure). Therefore, the liquefaction of unsaturated soils also depends on the initial confining pressure. Based on this concept, the liquefaction potential of unsaturated soil can be evaluated by comparing the volume compressibility of the soil particle skeleton and the volume change of the pore air required to bring about a zero effective stress state.