膨润土衬垫溶质扩散及渗透行为COMSOL模拟

COMSOL simulation of solute diffusion and infiltration behavior of geosynthetics clay liner

针对填埋场膨润土衬垫(GCL)易于被化学溶质击穿的问题,研究了化学溶质在GCL中的扩散行为和破坏机理,以指导工程实际。通过COMSOL Multiphysics构建膨润土扩散柱数值模型,研究了离子种类、离子浓度、水头压力以及上覆应力等因素对化学溶质在GCL中扩散行为的影响,并研究了渗透系数与扩散系数之间的转换关系。结果表明,阴离子比阳离子的扩散衰减速率小,扩散速率随溶质扩散时间的增长而减小,化学溶质的扩散会显著增加溶质浓度梯度的变化。对于扩散系数较大的溶质,孔隙率和扩散系数能较好地表征其扩散行为。上覆压力会明显增大化学溶质在GCL中的扩散。低、中浓度初始扩散源的扩散范围较浅,而高浓度初始扩散源的扩散范围较大。因此,在垃圾填埋场工程中,应根据渗沥液浓度、离子种类以及上覆垃圾荷载等对GCL的防污性能进行安全评估,尤其应对高浓度和高应力作用下较深范围内污染物的迁移情况进行监测。本研究结果可为GCL在填埋场中的工程应用和防污安全预警提供参考。

Regarding to the chemical break-down of the geosynthetics clay liner(GCL)in landfill,the diffusion behavior and the failure mechanism was numerically studied to guide engineering practice.A serious of COMSOL Multiphysics numerical model was developed based on the diffusion column tests.The effects of chemical ionic species and concentrations,the water gradient and the overlying pressure on the diffusion behavior of the GCL were investigated.A relationship between the hydraulic conductivity and diffusion coefficient was exploded.The results demonstrated that the decays rate of anion diffusion was lower than that of cations.The diffusion rate was gradually decreased with the time.The chemical diffusion accelerated the change of the solution gradient.The porosity and diffusion coefficient can screen well the diffusion behavior of the GCL with larger diffusion coefficients.Under a certain water gradient,the overlying pressure increased the chemical diffusion through the GCL at the initial stage,and moved to a deeper position.The low and medium concentrations influenced the area nearby the initial diffusion source.However,the initial diffusion source with high concentration influenced a larger area.Therefore,the chemical diffusion and hydraulic performance of GCL in a landfill project should be evaluated carefully according to the concentration of leachate,the type of chemical ions,and the overlying pressure.The migration of pollutants should be monitored,especially relating to the high chemical concentration and high-pressure condition.The research results provided a theoretical reference for the application of GCL in landfills,as well as the risk assessment and early warning systems.