城市中心污染场地一般采用阻隔墙防止有害物质扩散,但干湿循环会影响污染场地阻隔墙的防渗性能。通过干湿循环后的柔性壁渗透试验和CT扫描研究干湿循环对砂–膨润土阻隔墙的抗渗性影响以及微观结构变化特征。结果表明:(1)砂–膨润土渗透系数k随着干湿循环次数的增加而增大,2~6次干湿循环的渗透系数k增幅最大,从1.33×10-7cm/s增大至6.05×10-5cm/s,增大了454倍;(2)结合CT扫描以及图像处理,发现试样的孔隙体积率随着干湿循环次数增加而增大,2~6次干湿循环的孔隙体积率从14.66%增大至25.39%,6次干湿循环后孔隙体积率增幅不大并趋于稳定;(3)干湿循环前期,试样的孤立孔隙不断萌发扩展,密度增大,6次循环之后连通孔隙开始出现,8次循环之后孤立孔隙完全演化为连通孔隙。
The polluted site in the city center generally uses a barrier wall to prevent the spread of harmful substances, but the drying-wetting cycles will affect the anti-seepage performance of the barrier wall in the polluted site. Through the flexible wall permeability test and CT scanning after drying-wetting cycles, the effect of drying-wetting cycles on the change of the impermeability of the sand-bentonite barrier wall and the characteristics of the microstructure change were studied. The experimental results show that: (1) The permeability coefficient k of sand-bentonite increases with the increase of the number of drying-wetting cycles, and the permeability coefficient of 2~6 drying-wetting cycles increased the most, from 1.33×10-7cm/s to 6.05×10-5 cm/s, increased by 454 times. (2) Combined with CT scanning and image processing, it is found that the pore volume ratio of the sample increases with the increase of the number of drying-wetting cycles, in the interval of 2~6 drying-wetting cycles, the pore volume ratio increases from 14.66% to 25.39%, after 6 drying-wetting cycles, the pore volume ratio does not increase much and tends to be stable. (3) In the early stage of the drying-wetting cycles, the isolated pores of the sample continued to germinate and expand, and the density increased, the connected pores began to appear after the 6th cycle; after the 8th cycle, the isolated pores completely evolved into connected pores.
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