高温后上海软黏土的土-水特性及微观机理试验研究

Experimental study on soil-water characteristics and micromechanism of Shanghai soft clay after high temperatures

土-水特征曲线(SWCC)是揭示非饱和土性状的主要本构关系,但对于100℃以上高温环境下软黏土的土-水特性研究很少。针对上海软黏土的常温(20℃)土样和105℃,150℃和200℃等高温加热4 h后的土样,采用气相法研究了高温作用后上海软黏土的土-水特征曲线随温度的变化,同时,通过扫描电镜(SEM)试验研究了高温后软黏土的土-水特性随温度变化的微观机理。试验结果表明100℃以上高温环境下上海软黏土的土-水特征曲线随温度升高呈逐渐下降趋势,说明随温度升高软黏土的持水能力下降,吸力降低,进气值减小。分析各温度下土样的SEM图像发现,土的总孔隙数量减少,但少量孔隙的孔径增大,从微观特征上说明了土-水特性随温度升高的变化趋势和变化机理。说明,孔隙数量和孔隙结构随温度升高发生的变化是导致软黏土的土-水特性随温度升高而变化的根本原因。

The soil-water characteristic curve (SWCC) is the main constitutive relation to reveal the properties of unsaturated soils.However, few researches on soil-water characteristics of unsaturated soils in high-temperature environment, especially over 100?C, have been reported.The SWCC of soft clay from Shanghai at high temperature is investigated using the vapor phase technique.Different temperatures (20?C, 105?C, 150?C and 200?C) are adopted to dry the soft clay for 4 h before testing the SWCC.In addition, the microstructures of soft clay before and after high temperature are characterized by scanning electron microscopy (SEM).The results show that the SWCC of soft clay decreases gradually as temperature increases to >100?C. Similarly, the water-retaining capacity, suction force and intake value of soft clay decrease with the increase of temperature. These results are mainly attributed to the variation of the microstructure of soft clay according to the SEM results.The number of pores of soils decreases, while the pore size of a small number of pores increases at high temperature, which accounts for the variation mechanism of SWCC of soft clay at high temperature.In a word, the change of pore number and pore structure with the increase of temperature is the fundamental reason for the change of water characteristics of soft clay with the increase of temperature.