饱和细粒土固结的三维多尺度结构演化及微宏观性质分析

Three-Dimensional Structural Evolution and Multiscale and Micro-Macro Property Analysis in the Consolidation of Saturated Fine-Grained Soil

饱和细粒土具有多物质多尺度共存的特殊性,其微观结构的形态演变是土体具有复杂工程特性的根本原因.本研究采用数据约束算法(DCM)结合多能量同步辐射X射线μCT技术,解决微观定量表征这一难题.基于物质对X射线吸收系数的差异,将土样材料分成孔隙、有机质和矿物质3个组分,进而表征了土样在不同固结压力下的物质赋存及多尺度三维结构演化特征.结果表明,饱和细粒土中孔隙与矿物质容易共存且互呈团絮状结构,弥散于土体中的有机质体积较小,多与孔隙重叠或位于孔隙与矿物团聚体交界处.当土样受压从0增加到1600 kPa时,孔隙连通程度减弱而矿物质贯通程度增强.固结压力超过400 kPa时,大孔隙连通体消失,微纳米尺度孔隙连通体开始出现.土体由大孔疏松状变成小孔密集状,微观结构变化不规律.细粒土结构的变化不仅与初始孔隙和矿物分布有关,也与固结压力有关.微宏观定量分析表明,饱和细粒土的力学特性与微纳米、纳米尺度的孔隙和矿物团聚体联系密切,这可为土体蠕变机制分析提供可行性理论和技术.

Saturated fine-grained soils have various compositions. In particular,the soil structural scale varies from nano-meter to macroscale. Micro properties can affect mechanical properties such as ground-bearing capacity. The exploration of quantitative micro properties and the quantitative relation between micro and macro evolutionary characteristics continues to challenge scientific research. In this study,both data constraint modelling (DCM) and multienergy synchrotron X-ray μ-CT were used to realize the quantitative characterization of microstructure. Soil sample compositions are classified into pores,organic matter,and minerals. Then,the occurrence and three-dimensional multiscale evolutionary characteristics of soil samples are studied under different pressures based on substance compositions. Results show that the pore and mineral are mixed together to forming soil aggregates. A small amount of organic matter is distributed in the soil. Organic matter is mostly contained in pores or located at the junctions of pores and mineral clusters. The connectivity degree between pores decreases and that between minerals increases as pressure is increased from 0 to 1 600 kPa. When pressure is more than 400 kPa,macro pore clusters disappear and micro-nano pore clusters begin to appear. Pore morphology changes from large to small and dense.The soil microstructure changes irregularly when the pressure increases. The structural change in saturated fine-grained soil is related to the initial pore and mineral distribution and to consolidation pressure. Quantitative analysis between micro and macro properties suggests that the mechanical property of saturated fine-grained soil is closely related to those of micro and nanoscale pores and mineral aggregates. The methods in this study can provide a feasible theory for soil creep mechanism analysis. The proposed method is applicable for the analysis of the micro and macro properties of other engineering materials like concrete.