黄土的细观结构演变与宏观结构性变化规律

Evolution of micro-structure and macro-structural property of loess

黄土作为一种欠压密的结构性土,其结构受固结、剪切、浸水等作用易发生破损变化,从而使力学特性随土结构演变而变化。从观察黄土细观结构演变的角度出发,通过微米CT试验测试了天然、重塑和饱和黄土初始结构、不同围压三轴固结完成结构及三轴剪切破坏结构,研究了重塑扰动和浸水饱和作用下土的细观结构变化,以及固结剪切变形的土结构演变特性,建立细观结构演变特征与宏观变形强度之间的联系。从土结构细观角度解释了土骨架变形的力学行为。主要成果包括:(1)饱和与扰动重塑改变土粒结合水膜,消除了土骨架中大孔隙分布,土孔隙均匀化分布。(2)同一围压条件下,随着土样固结剪切变形发展,大孔隙趋于减小。原状土固结完成时,仍有比较明显的大裂隙;剪切破坏时,土产生明显的剪缩变形,土骨架中大孔洞分布显著减少。(3)与原状土比较,重塑土土骨架分布更加均匀,剪坏时的大孔隙基本闭合。饱和与固结剪切作用可使得原状土的大孔隙完全消失。(4)控制不同应变水平加卸载作用,揭示土结构性的构度随综合塑性应变的增大而减小,土的强度也减小。

As a kind of under-compacted structural soil,the loess is easily damaged by consolidation,shear and Immersion,which makes the mechanical properties change with the evolution of soil structure.From the point of view of observing the evolution of loess micro-structure,the initial structures of natural,remolded and saturated loesses,the triaxial consolidation completed structure with different confining pressure and the triaxial shear failure structure are tested by the micron CT tests.The mechanical behavior of the deformation of the soil skeleton is explained from the perspective of soil structure.The main results include:(1)The saturation and disturbance remodeling change the soil-particle-bound water film,eliminate the distribution of large pores in soil skeleton,and homogenize the distribution of soil pores.(2)Under the same confining pressure conditions,the macropores tend to decrease with the development of the consolidation shear deformation of soil samples.When the consolidation of undisturbed soil is completed,there are still obvious large cracks,and when the shear failure occurs,the soil produces obvious shear shrinkage deformation,and the distribution of large holes in the soil skeleton is significantly reduced.(3)Compared with the undisturbed soil,the remolded soil has more uniform distribution of skeleton,and its macropores are basically closed when shearing.The saturation and consolidation shear can make the macropores disappear completely.(4)By controlling the loading and unloading with different strain levels,it is revealed that the structural degree of soil structure decreases with the increase of the comprehensive plastic strain,and the strength of soil also decreases.