干湿循环与盐溶液作用下红黏土-膨润土混合土体变与渗透特性

VOLUME CHANGE AND PERMEABILITY CHARACTERISTICS OF RED CLAY-BENTONITE MIXTURES UNDER WETTING-DRYING CYCLESAND SALT SOLUTION INFILTRATION

针对红黏土-膨润土混合土材料在干湿循环作用及复杂化学环境下的性能演化问题,开展了盐溶液入渗作用下红黏土-膨润土混合土的干湿循环试验研究,分析了干湿循环次数、膨润土掺入比、盐溶液浓度对压实混合土材料体变特征与渗透特性的影响,并结合压汞试验揭示了试样收缩变形与渗透系数变化的微观机制。结果表明:随着干湿循环次数的增加,压实红黏土-膨润土混合土试样累计收缩变形逐渐增大,收缩趋势随入渗盐溶液浓度的增加而增大;干湿循环过程中试样渗透系数呈先增大后减少的趋势,且随着盐溶液浓度增加而逐渐降低;增大混合土中膨润土掺量可以提高试样化学相容性,减少胀缩变形并减小渗透系数。压汞试验表明,盐溶液入渗及干湿循环作用导致土体孔隙“双峰”分布特征减弱,土体中的大孔数量及孔径减小,小孔略有增多;随着入渗的盐溶液浓度增加,小孔变化不明显,而土体总孔隙率及大孔数量减小,进而导致土体收缩变形增大、渗透系数减小。

To inv estigate the performance evolution of red clay-bentonite mixtures concerning wetting-drying cycles and chemical conditions,volume change and permeability tests were conducted on red clay-bentonite mixtures under salt solution infiltration and wetting-drying cycles.The effects of wetting-drying cycles,bentonite contents,and salt solution concentrations on the compacted mixtures were analyzed.The microscopic mechanisms of shrinkage and hy-draulic conductivity after different wetting-drying cycles were revealed through mercury intrusion porosimetry(MIP)tests.Experimental results demonstrated that the shrinkage of compacted soil samples increases gradually with an in-crease in wetting-drying cycles and salt solution concentration.The hydraulic conductivity of the soil samples increases first and then decreases during the wetting-drying cycles.Meanwhile,the addition of bentonite improves the chemical capacity of the soil samples and has the potential to decrease hydraulic conductivity and volume change.MIP test re-sults revealed that the total pore volume and the macro-pore diameter of the soil samples decrease after wetting-drying cycles,and the bimodal characteristics of the pore distribution curves weaken.Furthermore,with an increase in salt solution concentration,the micro-pores remain constant,and the porosity of the soil decreases with a decrease in macro-pores,resulting in greater shrinkage deformation and decreased hydraulic conductivity.