增湿过程花岗岩残积土微观结构演变规律

Microstructural changes of granite residual soil during humidification process

摘要:

为探明花岗岩残积土在增湿过程中微观结构变化特征,采用电镜扫描试验,通过PCAS软件分析土体非饱和饱和状态下孔隙变化,实现孔隙结构的定量表征,并通过核磁共振试验分析土体非饱和饱和状态的T₂曲线,进一步分析其三维分形维度特征。研究结果表明:非饱和状态下,随着含水率的增加,整体呈现较小孔隙数量减少、而较大孔隙增多的趋势,小的团粒在此过程中吸纳粗颗粒扩大形成较大团粒；达到饱和状态后,团粒解体,呈现相反的发展趋势;基于横向弛豫时间（T₂）可将孔隙分为团粒孔隙、粒间孔隙、微裂隙3类,其中粒间孔隙受孔隙水影响最为显著,团粒孔隙和微裂隙受孔隙水影响则较弱；三维结构分形维度随含水率提高而呈现降低趋势,并与含水率具有指数函数关系。对花岗岩残积土增湿过程中微观结构变化规律的研究为分析花岗岩残积土群发性滑坡的启动机理提供理论依据,通过监测土体含水率变化可预判孔隙结构演化阶段,结合分形维度模型可建立边坡稳定性评价指标,为闽粤丘陵区花岗岩残积土滑坡预警提供了关键判据。

Abstract:

In order to explore the characteristics of microstructural changes of granite residual soil during wetting, the electron microscope scanning test was used to analyze the pore changes of the soil under unsaturated-saturated state by PCAS software to achieve quantitative characterization of the pore structure, and the three-dimensional fractal dimension characteristics were further analyzed by analyzing the T₂ of the soil under unsaturated-saturated state by nuclear magnetic resonance test. The research results show that under unsaturated state, with the increase of water content, the number of smaller pores decreases and the number of larger pores increases. In this process, small aggregates absorb coarse particles to expand and form larger aggregates; after reaching the saturated state, the aggregates disintegrate and show the opposite development trend; reaching the saturated state. Based on the transverse relaxation time (T₂), the pores can be divided into three categories: aggregate pores, intergranular pores, and microcracks. Among them, intergranular pores are most significantly affected by pore water, while aggregate pores and microcracks are less affected by pore water; the three-dimensional structural fractal dimension shows a decreasing trend with the increase of water content, and has an exponential function relationship with the water content. The study on the change law of microstructure during the wetting process of granite residual soil provides a theoretical basis for analyzing the initiation mechanism of mass landslides of granite residual soil. The microstructure evolution stage can be predicted by monitoring the changes in soil moisture content. The slope stability evaluation index can be established by combining the fractal dimension model, which provides a key criterion for early warning of granite residual soil landslides in the hilly areas of Fujian and Guangdong.