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膨胀土普遍发育有微孔隙与微裂隙形成特殊的微结构,在不同环境条件下脱湿,其内部微观结构会发生剧烈变化。采用扫描电镜法和压汞法相结合的方法,对相同初始状态重塑膨胀土样在不同环境下脱湿前后内部孔隙变化进行研究,探讨不同环境条件对膨胀土微观结构变化规律,主要得出以下结论:1膨胀土样脱湿干燥时孔隙收缩,土中的大孔隙变为小孔隙,导致小孔隙和超微孔隙增多,土样中的总孔隙体积减小;2烘箱环境下高温脱湿时土体表面和内部会出现微裂隙,不同孔隙孔径分布曲线为三峰曲线;冻干法干燥过程中不会导致土体中的孔隙收缩,基本不改变土样内部结构;风干法脱湿时不同孔隙孔径分布曲线为三峰曲线,但峰值明显低于高温脱湿;恒温恒湿条件下脱湿时主要表现为小孔隙,孔径大于1μm的孔隙体积极小;3膨胀土在不同脱湿环境下脱湿后总孔隙累积体积大致是随温度升高而增加,其中孔径小于1μm孔隙体积占总孔隙的比例随温度升高而减少,而孔径大于1μm孔隙占总孔隙的比例随温度升高而增加;4电镜实验表明重塑膨胀土的孔隙主要是黏土集聚体之间的孔隙和黏土集聚体内部片状矿物的叠聚而形成的微小孔隙,表面特征复杂,孔隙之间的连通情况不好,脱湿前结构单元体呈片状且连接紧密、片状表面平直,脱湿后颗粒边缘更加清晰可见、片状呈卷曲状,且片状连接有脱离的迹象。
In general, expansive soils have micro-pores and micro-cracks that form special microstructures. When they sweat under different environmental conditions, their microscopic structure will change drastically. Using the combination of SEM and mercury intrusion porosimetry, the change of internal porosity before and after desiccation of the same initial state reshaped soil samples was studied, and the variation of microstructure of expansive soil under different environmental conditions was discussed. The main results are as follows Conclusions: 1 When the expansive soil samples dehumidify and dry, the pores shrink, and the macropores in the soil become small pores, resulting in the increase of small pores and ultramicroscopic pores and the decrease of the total pore volume in the soil samples. The micro-fissures will appear on the surface and inside the soil, and the distribution curve of different pore sizes will be a three-peak curve. The freeze-drying process will not cause the pore shrinkage in the soil and will not change the internal structure of the soil. The pore size distribution curve is a three-peak curve, but the peak value is obviously lower than that of the high-temperature dehumidification. The small pore size is mainly seen when desiccating under constant temperature and humidity conditions, and the pore volume with pore size larger than 1μm is extremely small. 3 The expansive soil is dehumidified under different dehumidification conditions The cumulative total pore volume increases with increasing temperature, of which the ratio of pore volume to total pore size with pore size less than 1μm decreases with increasing temperature, whereas the pore size larger than 1μm occupies the total pore volume 4 increased with the increase of temperature.4 Electron microscopy experiments showed that the pores of remolded expansive soil are mainly micro-pores formed by the agglomeration of clay aggregates and the lamellar minerals in the clay aggregates. The surface features are complex and the pores Between the connection is not good, before dehumidification structural unit was flaky and closely connected, the flat surface of the sheet, after desiccation the edge of the particles more clearly visible, flaky crimp, and flake connection with signs of detachment .