Evaluating leakages through GMB/GCL composite liners considering random hole distributions in wrinkle networks

This paper presents a study on the development of a hydraulic connectivity analysis-based approach for evaluating leakage rates through geomembrane (GMB)-geosynthetic clay liner (GCL) composite liners considering random hole distributions in a GMB wrinkle network. An algorithm for hydraulic connectivity analysis was developed to find the hydraulically connected wrinkles from a wrinkle network, and an explicitly expressed criterion is proposed to define the hydraulic connection between wrinkles under the assumption that only one of the two adjacent wrinkles is possible to be damaged. A Monte Carlo simulation was used to evaluate the probability weighted average of the total leakage through multiple randomly distributed holes considering numerous possible combinations of locations of holes. The proposed approach was applied to typical examples reported in the literature and shows that it can objectively quantify the effect of the hydraulic properties of the liner and overburden pressure on the hydraulic connectivity between wrinkles in a wrinkle network. The proposed approach also allowed assessing the effect of different probabilities of various hole distributions on the calculated leakage, which was demonstrated to be non-negligible, especially when the hole frequency is small.     

复合衬垫中污染物一维瞬态扩散–对流运移规律研究

采用GMB(土工膜)/GCL(膨润土防水毯)/SL(土质垫层)复合衬垫全瞬态扩散–对流运移解析模型,考察了对流区域对污染物运移计算结果的影响;探讨了用渗滤液水头高度替代衬垫水头差的简化计算的可行性;探究了土工膜类型对复合衬垫防污阻隔性能的影响;分析了对流、扩散、吸附作用对渗沥液中典型有机污染物运移规律的影响.研究结果表...     

Analytical model for coupled consolidation and diffusion of organic contaminant transport in triple landfill liners

A triple-layer composite liner consisting of a geomembrane liner (GMB), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) is commonly used at the landfill bottom liner system to isolate the contaminated leachates. In this paper, one-dimensional quasi-steady-state small deformation model (SDSS) was developed to investigate the behavior of organic chemicals transport in landfill composite liner system considering coupled effect of consolidation, diffusion and degradation. The first and second type bottom boundary conditions are used to derive the analytical solutions. The generalized integral transform technique (GITT) is adopted to derive the analytical solutions. The effect of consolidation on the performance of GMB/GCL/CCL with intact or leaking GMB is investigated. The triple liner under double drainage boundary condition (DDBC) has better performance compared to the case under single drainage boundary condition (SDBC). This is because the velocity induced by consolidation under DDBC is lower than that under SDBC. The effect of GCL consolidation shows an opposite trend compared to CCL consolidation. Considering GCL consolidation can increase the breakthrough time. The effective diffusion coefficient of GCL can be two magnitude orders smaller after consolidation, which provides a better diffusion barrier for the chemical transport. The effects of adsorption and degradation have been analyzed as well. Increasing the adsorption capacity of a deforming composite liner can increase the steady-state bottom flux, which shows the opposite tendency compared to the case without considering consolidation. This is due to the fact that for the case of a deforming composite liner, the advection induced by consolidation includes a new term due to the solid velocity. This velocity will result in the increase the mass of chemical migration through the composite liner.     

Assessment of consolidation-induced VOC transport for a GML/GCL/CCL composite liner system

In municipal solid waste landfills, a triple-layer composite liner consisting of a geomembrane liner (GML), a geosynthetic clay liner (GCL) and a compacted clay liner (CCL) is commonly used at the landfill bottom to isolate the leachates from surrounding environment. This paper presents a numerical investigation of the effect of liner consolidation on the transport of a volatile organic compound (VOC), trichloroethylene (TCE), through the GML/GCL/CCL composite liner system. The numerical simulations were performed using the model CST3, which is a piecewise linear numerical model for coupled consolidation and solute transport in multi-layered soil media and has been extensively validated using analytical solutions, numerical solutions and experimental results. The performed numerical simulations considered coupled consolidation and contaminant transport with representative geometry, material properties, and applied stress conditions for a GML/GCL/CCL liner system. The simulation results indicate that, depending on conditions, consolidation of the GCL and CCL can have significant impact on the transport results of TCE (i.e., TCE mass flux, cumulative TCE mass outflow, and distribution of TCE concentration within the GCL and CCL), both during the consolidation process and long after the completion of consolidation. The traditional approach for the assessment of liner performance neglects consolidation of the GCL and CCL and fails to consider the consolidation-induced transient advection and concurrent changes in material properties and, therefore, can lead to significantly different results. These differences for with and without the consolidation effects can range over several orders of magnitude. The process of consolidation-induced contaminant transport is complex and involves many variables, and therefore case-specific analysis is necessary to assess the significance of liner consolidation on VOC transport through a GML/GCL/CCL composite liner system.     

挥发性有机化合物在复合衬里中的一维扩散解

土工膜和粘土衬里组成的复合衬里已广泛用于填埋场的防渗。有机挥发性化合物在复合衬里中迁移时,其主要的机理是分子扩散作用。本文建立了有机挥发性化合物在复合衬里中的一维扩散模型,并得到了解析解。将该解析解和以往给出的数值解法作了比较,发现两者得到的结果较为接近,从而验证了本文解的可靠性。基于本文计算模型,分析了三种常用复合衬里对挥发性有机化合物的防渗性能。研究发现对于挥发性有机化合物甲苯,土工膜和GCL组成的复合衬里的浸出液总量要比土工膜和较厚粘土衬里组成的复合衬里大好几个量级。