饱和细粒土固结过程中三维微观空架结构研究

饱和细粒土具有典型的多尺度孔隙三维空架结构,显著影响着土体固结沉降等宏观力学特征。基于SEM及多能量同步辐射X射线μCT技术结合数据约束算法(DCM),建立饱和细粒土多尺度结构三维微观模型。研究结果表明:土样受荷时土体表面的表观孔隙率与体积孔隙率的变化趋势基本一致,但表观孔隙率略小于体积孔隙率。800 kPa压力是土样表面表观孔隙率随压力变化的转折点,土体在800 kPa压力时其微观结构发生了显著变化,可能对应着土体骨架的蠕变变形。100 kPa土样和800 kPa土样表面的平均孔隙形状系数出现异常,100 kPa时低于均值0.32,而800 kPa时显著高于0.32,表明土体中孔隙在受压初始阶段对压力变化较敏感,而在固结后期土体结构发生变化。土样的实验孔隙率略大于由DCM计算出的体积孔隙率和DCM导出二维切片的表观孔隙率,经DCM二维切片得到的土样平均表观孔隙率在0.35～0.45范围内波动。数据约束模型突破分辨率限制,实现微纳米级颗粒的三维结构表征,同时PCAS检验数据约束模型切片数据可为计算土体孔隙率提供新途径。

Three-dimensional pore evolution analysis in consolidation of saturated fine-grained soil

The saturated fine-grained soil has a typical multi-scale three-dimensional overhead structure and its complex micro-morphology significantly affects the consolidation settlement and other macro-mechanical characteristics. Based on the scanning electron microscopy (SEM), a three-dimensional micro-model for saturated fine-grained soil with multi-scale structure is established by using the multi-energy synchrotron radiation X-ray micro-CT technology combined with the data constrained algorithm (DCM). The results show that the change trend of apparent porosity of soil surface is basically the same as that of volumetric porosity, while the apparent porosity is slightly smaller than the volumetric one. The pressure of 800 kPa is the turning point of apparent porosity of soil samples with pressure. It is presumed that the microstructure of soil changes remarkably at the pressure of 800 kPa, which may correspond to creep deformation of soil skeleton. The average pore shape coefficients of 100 kPa and 800 kPa are abnormal, lower than 0.32 at 100 kPa and significantly higher than 0.32 at 800 kPa, which indicates that the pore in soil is sensitive to pressure change at the initial stage of compression, while the soil structure changes at the later stage of consolidation. Both the volumetric porosity calculated by DCM and the apparent porosity of DCM two-dimensional slices are slightly lower than the experimental porosity of soil samples. The average apparent porosity of soil samples obtained by DCM two-dimensional slices fluctuates in the range of 0.35 to 0.45.The DCM may break through the resolution limitation and realize the characterization of micro-nanoparticles. Meanwhile, the DCM tested by the PCAS can provide a new way to calculate soil porosity.