Investigation On The Regularity Of Contaminant Transport And Transformation Through Large-deformation Clay Barriers

In construction of the dredged sludge heap site and the simple waste landfill site, it is usually chose the thick clay layer as the natural impervious barrier. As the increasing height of waste loading on the surface, the clay layer will undergo a large-deformation consolidation, so it has to take the deformation of the thick clay layer into account in the investigation of the regularity of the contamination transport and transformation through the clay barrier,. In this paper, we theoretically investigate this proposition, a one-dimensional, nonlinear large-deformation transport-transformation model of coupled consolidation and contaminant transport-transformation model is derived. The innovation of the model is the consideration of the coupled function of the clay self-weight and the function of biodegradation, then the paper gives the numerical solution of the model equations, studies the transport and transformation regularity of the contaminant through the deforming clay barrier and the role of each parameter played in the equation, and the following conclusions can be drawn:1,The sorption of the contaminant on the soil particles plays a main role in the obstructing capacity of the barrier. The breakthrough time of the barrier with consideration of the solute sorption is several times longer than that without. Taken the solute sorption into consideration, the consolidation will reduce the breakthrough time of the contaminant across the liner and acceleration the transport, while in the absence of sorption, the consolidation will lengthen the transit time, and retard the process of the contaminant transport. This conclusion would have a large effect on the design of the clay barrier.2,With the thickness of the clay barrier increasing, the breakthrough time and transit length of the contaminant across the liner is lengthened too. If the clay layer is thicker 67%, the transit time can increase more than one time, the transit time would not lengthen in this ratio of course, but it is proved that a little increase of the layer thickness will produce remarkable increase on the breakthrough time.3,The transit time of the contaminant grows with the decreasing of the void ratio, it is proved that void ratio is the basic parameter among the hydraulic conductivity, the consolidation coefficient, the pre-consolidation stress, the other parameters have influence on the breakthrough time through taking effect on the void ratio. But the void ratio and consolidation coefficient are not the lower the better, by calculation, the proper magnitude of void ratio matched with the relevant consolidation coefficient can play the best performance of the obstruction.4,The coefficient of hydrodynamic dispersion affect a lot on the regularity of the transport, while the dispersion coefficient decreasing in the series rate the transit time will increase in the progression ratio, it should be noted that the diffusion term play the main role in the contaminant transport equation. The proper control on dispersion coefficient will obviously influence the result of breakthrough time of the contaminant.5,The biodegradation effect will not be seen at the beginning of the transformation rule, but in the long term,the biodegrade of the contaminant will incredibly reduce the growth rate of the contaminant concentration. It means a lot in evaluating the long term obstructing capacity of the barrier.The results of the investigation show that the non-linear large-deformation of the thick clay layer can't be neglected in the regularity of the transport and transformation of the contaminant through the natural thick clay layer. This conclusion would provide good suggestion on the study of the obstructing capacity of the natural thick clay barrier.