颗粒膨胀对膨润土复合衬垫防渗性能的影响及介观机制分析

Effect of particle swelling on hydraulic performance and meso-mechanism of geosynthetic clay liners

膨润土复合衬垫(geosynthetic clay liners,GCL)的防渗性能与膨润土颗粒水化后的多孔介质特性密切相关。通过建立去离子水环境下颗粒尺度GCL渗流的COMSOL数值计算模型,量化研究了颗粒膨胀对GCL有效孔隙率、迂曲度以及渗透系数的影响。研究结果表明,介观尺度膨润土颗粒的膨胀是影响GCL整体有效孔隙率、迂曲度及最终渗透系数的关键因素。膨润土颗粒膨胀会明显影响流径数量及流径通道宽度。当GCL的渗透系数接近10^(-11)m/s量级时,存在一条明显的主流径,初始孔隙率从0.5上升至0.6时,颗粒膨胀后的有效孔隙率从0.07上升至0.11,最小流径通道的宽度约为0.001 mm,大约为水分子的2500倍。随着膨润土颗粒的膨胀,GCL内主流径迂曲度逐渐增加。当初始细颗粒直径为0.1 mm,初始孔隙率从0.5增加至0.6时,GCL内主流径迂曲度在1.2~1.4之间,但所有初始孔隙率下的主流径迂曲度变化范围在0.07左右。同时,渗透系数接近10^(-11)m/s量级时,膨润土颗粒膨胀对GCL渗透系数的影响非常显著,当孔隙膨胀率大于0.96后,孔隙膨胀率增加了0.01,GCL的渗透系数会迅速下降一个数量级。

The hydraulic performance of geosynthetic clay liners(GCL)is closely related to the swelling characteristics of the bentonite particles and the resulting porous medium.However,there currently needs to be more analysis at the mesoscopic level to understand the permeating mechanisms.A numerical model using COMSOL was developed to study the effects of particle swelling on the effective porosity,tortuosity,and hydraulic conductivity of GCL under deionized water actions.The results demonstrate that the swelling of bentonite particles is a crucial factor influencing the effective porosity,tortuosity,and hydraulic conductivity of GCL.Particle swelling significantly affects the width and number of flow paths.When the hydraulic conductivity of GCL approaches the order of 10^(−11)m/s,a distinct main flow path exists.With an initial porosity increasing from 0.5 to 0.6,the effective porosity after particle swelling rises from 0.07 to 0.11.The width of the minor flow path is approximately 0.001 mm,which is about 2500 times the size of a water molecule.As the bentonite particles swell,the tortuosity of the main flow paths within the GCL gradually increases.For an initial particle size of 0.1 mm and an initial porosity rising from 0.5 to 0.6,the tortuosity of the main flow path ranges from 1.2 to 1.4.However,the variation in tortuosity for all initial porosities is around 0.07.Meanwhile,when the hydraulic conductivity of GCLs approaches the order of 10^(−11) m/s,the bentonite particle swelling significantly affects the permeability of GCL.After the pore’s swelling ratio exceeds 0.96,a 0.01 increment in the pore’s swelling ratio results in a rapid decrease in the hydraulic conductivity of GCLs by one order of magnitude.These findings shed light on the mesoscopic behavior of GCL hydraulic performance,particularly the influence of bentonite particle swelling on the effective porosity,tortuosity,and hydraulic conductivity of GCL.