Numerical analysis of evolution of the unsaturated soil micro-structure with capillary action during compression
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摘要:
研究非饱和土微结构的动态演化规律对认识非饱和土宏观物理力学行为的本质有重要意义。然而目前岩土学界对此尚不清楚。文章提出利用毛细水算法进行非饱和土压缩数值试验，研究其宏观变形过程中土水作用与孔隙的演变规律。首先参考黄土骨架颗粒的形态和优势颗粒的大小，建立了540 μm×400 μm理想的非饱和土微观结构模型；其次利用毛细水模型计算某一含水率下水分分布及毛细力，并将此毛细力施加于土粒之间；然后施加外荷载，对含水率为5%、10%、18%的3个模型土样进行压缩模拟。模拟结果表明：模拟获得的压缩曲线与同工况试验曲线表现出了相同的变化规律，表明该模拟一定程度上能够反映土体在压缩过程中的宏观变形特征；在压缩过程中，随土体的变形，饱和度和基质吸力分别呈上升和下降趋势，且变化程度与含水率有关，表现为含水率越高，饱和度涨幅越大，而基质吸力却在土样干燥和近饱和时降幅较大；土体孔隙结构的演化形式与体积含水率有关，低含水率时孔隙以收缩变形为主，高含水率时以大孔隙压密为更小类型的孔隙为主。模拟结果可作为实验结果的有益补充，加深对土体宏观变形行为的认识。
Abstract:Using numerical method to investigate the evolution of micro-structure in unsaturated soil is helpful to explain their physical mechanical. However, the evolution of micro-structure in unsaturated soil is not clear. For this reason, the capillary method is proposed to simulate compression test of unsaturated soil for analyzing soil-water interaction and evolution of pore spaces. In this research, an ideal micro-structure soil model of 540 μm×400 μm is established according to the shape and size of skeleton particles of loess. The capillary method is used to calculate the capillary water distribution and capillary force under different water content(5%, 10%, 18%), and the force then acts on the wetting surface among particles. The loading is applied to the soil sample. The compression test of unsaturated soil is simulated in this research. The simulation results show that the characteristics of compression curve are in good agreement with the experiment data, indicating that the numerical test can reflect the unsaturated soil deformation behavior under the condition of compress. Moreover, the saturation increases and matric suction decreases with the compression of the soil; the saturation increases most at high water content; the matric suction decreases least at middle water content; the deformation pattern is related with the moisture, namely, the pores are mainly shrunk at low water content while mainly disintegrated at high water content. The simulation results are a very useful supplement to laboratory test to explore the deformation mechanism of unsaturated soil.
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表 1 模型参数表
Table 1. Parameters in the model
单元 密度
/（g∙cm−3）弹模
/GPa泊松比 摩擦角
/（°）黏聚力
/kPa接触角
/（°）表面张力
/（mN∙m−1）土颗粒 2.65 10.0 0.30 30.0 0.0 10.0 72.75 样盒 8.96 108.0 0.32 0.0 0.0 179.0 0.00 
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