不同脱湿环境下高含水率膨胀土微观结构变化特性试验研究

Study on Micro Structure of Expansive Soil with High Water Content under Different Dehydration Conditions

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。

The micro pores and micro cracks formed special micro structure in the expansive soil. the internal microstrueture of expansive soil is changed in different dehydration conditions, The MIP and SEM were used to study micro-structure of dehydration expansive soil, The changes of internal porosity in different conditions are stud- ied, the conclusions are as follows： ①The pores of expansive soil shrank and the large pores became small when expansive soil dehydration, as a result, small pores and micro pores increased and the total pore volume of soil sample decreased. ②Micro-cracks appeared in the soil surface and internal when the expansive soil drying under the environment of high temperature, different pore size distribution curve was a three peak curve ; Soil pore was shrank in the frozen drying process, and the internal structure of soil was not change basically; the different pore size dis- tribution curve of open-air drying soil was a three peak curve, but its peak value was significantly lower than that of high temperature desorption; there was mainly small pore under the condition of constant temperature and humidity dehumidifying. ③The total pore volume of expansive soil was increased with the increase of temperature, and the pore volume which aperture less than 1 p.m decreased with the increase of temperature, while the pore volume which aperture more than 1 μm increased with the increase of temperature. ④he SEM experiments showed that ： the pores of expansive soil were formed by the accumulation of pores and clay particles, the surface features were complex, the connectivity of the pores was not good, and the structural units were lamellar and even close and flat before dehydration, the edge of particles was more clearly visible and coiled and the sheet detachment after dehy- dration.