非饱和与饱和黄土统一性动力响应机制试验研究

Laboratory tests on the unified response mechanism of unsaturated and saturated loess under dynamic loadings

动荷载作用下,非饱和与饱和天然黄土在直观表现上显著不同,前者以震陷(动残余应变)为特征,后者则表现为液化现象.基于室内静(动)三轴试验、土水特征曲线测试,结合天然黄土的水、气两相在固相介质中的渗透性,研究固、水、气三相介质控制黄土应力响应过程的差异性作用,揭示天然黄土动残余应变与液化在动力响应机制上的统一性.试验分析结果表明:不同加载过程中,加载应力与残余变形、残余变形与孔隙压力的相关系数,普遍高于加载应力与孔隙压力的对应量值;相较固相介质响应外部荷载作用的变形过程,水、气两相的响应明显具有受限于固相介质变形的特征;固相介质的受载变形和水、气两相介质的低渗透性,是黄土动力响应过程中孔隙压力增长的决定性因素;非饱和与饱和黄土在直观现象上的差异,与水、气相在渗透性与可压缩性方面的显著差别密切关联.

The behaviors were obviously different between unsaturated and saturated loess under dynamic load- ings. Generally, the former suffered from seismic subsidence （dynamic residual strain） while the latter brought about liquefaction. Based on laboratory tests of static/dynamic triaxials, soil-water characteristic curve and per- meability of water and air, the key roles of tri-phases of solid, water and air were analyzed in controlling the stress response process of natural loess. The uniformity of the response mechanism was confirmed for the dy- namic residual strain and the liquefaction of loess. The testing results revealed that, during different loading pro- cesses, the degree of correlation between external loading and residual deformation （or between residual defor- mation and pore pressure） was generally greater than the value between external loading and pore pressure.This could provide a proof that the residual deformation of solid phase of loess would be directly caused by external loadings, whereas the water and air in void indirectly responded to the loading through a compressed way generated by solid particles. While the pore pressure of natural loess should be generated under external loadings, the determining factors might be the de- formation of the solid phase and the lower permeability of water and air phases. As a result, the distinct difference between dy- namic residual strain and liquefaction of loess primarily should be related to the difference of permeability and compressibility between water and air.