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石碑塬滑坡是1920年海原地震触发的大型黄土流滑,认识其破坏特征与发生机制对于黄土边坡长距离液化失稳机制的研究非常重要。对石碑塬黄土滑坡的调查和研究表明,饱和黄土或高含水率黄土具有很高的液化势和流态破坏势,在强震作用下,饱和黄土易发生液化或流滑。对石碑塬滑坡的7组原状黄土样品进行振动三轴剪切试验,并结合其微观特征分析,探讨了循环振动荷载作用下的饱和黄土孔隙水压力-应变增长模型,分析了振动液化过程中液化应力比与黄土粒度组成、土体微观结构参数及饱和度之间的关系。结果表明:黏粒含量越低,振动作用下饱和黄土孔隙水压力响应越快,液化应力比越低;黄土孔隙比越大,孔隙结构分形维数越大,液化应力比越低,振动液化后黄土孔隙分形维数降低,结构较液化之前更为致密;饱和度对黄土粒间胶结物质的赋存状态及黄土结构强度影响很大,同一土体饱和度越高,溶滤于孔隙水中的离子浓度越高,土体粒间接触点(或胶结点)越容易发生断裂,使得黄土结构强度降低,液化应力比降低。
The Shibeiyuan landslide is a large-scale loess slippery triggered by the Hailang earthquake in 1920. It is very important to understand the characteristics and mechanism of its failure for the long-distance liquefaction instability mechanism of loess slopes. The investigation and research on the loess landslide in the tablet monument shows that the saturated loess or high water content loess has high liquefaction potential and fluid damage potential. Saturated loess is prone to liquefaction or slippery under strong earthquake. Three groups of intact loess samples from Shibeiyuan landslide were subjected to triaxial shear tests. Combined with the analysis of their microscopic characteristics, the pore water pressure-strain growth model of saturated loess subjected to cyclic vibration loading was discussed. The effects of liquefaction Stress ratio and the composition of loess, soil microstructure parameters and the relationship between saturation. The results show that the lower the clay content is, the faster the response of pore water pressure to saturated loess is and the lower the liquefaction stress ratio is. The larger the loess porosity ratio is, the larger the fractal dimension of pore structure is, the lower the liquefaction stress ratio is. The fractal dimension of loess pore decreases, and the structure is more compact than that before liquefaction. Saturation has a great influence on the occurrence state of intergranular cement and loess structural strength. The higher the saturation of the same soil, The higher the concentration, the more likely the soil grains will contact with each other at the point of contact (or the cementing point), resulting in a decrease in the strength of the loess structure and a decrease in the liquefaction stress ratio.