CaCl_2溶液对不同黏土基防渗墙渗透性的影响

Influence of CaCl_2 solution on the permeability of different clay-based cutoff walls

在垃圾填埋场和场地污染防治工程中,黏土基防渗墙作为原位屏障,已广泛应用于隔离污染物与控制污染地下水的迁移。由黏土与地层混合形成的防渗墙与CaCl_2溶液相互作用后,其渗透性会发生怎样的变化。针对这一问题,使用福建标准砂模拟砂性地层,以4种黏土作为混合材料,通过混合、浇筑和固结以后,对其渗透系数和水分特征曲线进行了实测。结果表明,在10%黏土添加量下,当4种砂-黏土混合土经0.2 mol/L CaCl_2溶液渗透稳定后,其渗透系数相比渗透液为自来水时都有不同程度的增大,但渗透系数增大的倍数没有超过10。此外,CaCl_2溶液在4种砂-黏土混合土中渗透稳定后试样的孔隙率没有发生较大变化,只是小幅地减小了。试验结果分析认为,钙离子与黏土矿物颗粒表面的单价阳离子发生了置换反应,使扩散双电层厚度减小,结合水含量降低,因而有效孔隙率增加,可能是宏观上造成渗透系数变大的主要原因。

Clay-based cutoff walls have been widely used as in situ barriers for contaminant isolation and controlling migration of the contaminated groundwater in landfills and site remediation engineering. With the interaction between CaCl2 solution and cutoff walls formed by mixing stratum of clays, what would happen to the permeability？ To explore this problem, the Fujian standard sand is used to simulate sandy stratum and four different clays are selected as addition material, and the specimens are consolidated after mixing and pouring. Then the permeability coefficient and moisture characteristic curves of specimens are measured by the improved flexible-wall permeameters and the centrifuge test. The results indicate that at the 10% adding level of clay, all the final permeability coefficients are increased after the four sand-clay mixtures are permeated with 0.2 mol/L CaCl2 solution. Compared with the tap water, and the increases of permeability coefficients are less than 10 times their original values. In addition, the porosities of four mixtures decrease only slightly. The experimental results imply that calcium ions may substitute those monovalent cations on the surface of clay mineral particles, leading to a decreases in the thickness of diffuse double layer and bound water, and hence the increase of effective porosity.