Theoretical Study Of Transport Through GCL In Landfill Based On Microscopic Analysis

Geosynthetic clay liner (GCL) is a good barrier material to be used in landfill, for its merits of little thickness, low hydraulic conductivity, and ability of self-healing and bearing non-uniform settlement. But hydraulic conductivity of GCL or bentonite in GCL is very sensitive to chemical interactions. The performance of GCL will be influenced by stress state and hydrated condition. Current test methods for transport parameters study are time-consuming and prone to be influenced by termination criteria. And the calculation of transport parameters fails to appropriately considerate the microscopy characteristics of bentonite, which makes it difficult to study chemical consistency of liner. The regulation of hydraulic conductivity and diffusion coefficient with dry density and concentration of pore solution was studied based on microstructure study, and the effectivity of GCL composite liner was evaluated. The study contained the following main parts.1. The bentonite microstructure characteristics, such as distribution and roughness of pore, apparent porosity and intraparticle void ratio, were studied quantitatively. The regulation of these characteristics with dry density and concentration of pore solution was obtained, which was the base of quantitative study for transport parameters.2. The calculation formula of the distance, d₂, between montmorillonite in intraparticle pores was deduced. Hydraulic conductivity of bentonite was obtained using d₂ and Poiseuille law. The regulation of hydraulic conductivity with void ratio and concentration of leachate was analyzed.3. Taking microstructure as medium, relationship between diffusion coefficient and hydraulic conductivity was developed, and calculation equation of diffusion coefficient was obtained. The equation was verified with measured diffusion coefficients. The regulation of diffusion coefficient with void ratio was discussed.4. Based on regulation of transport parameters with void ratio, solute transport through GCL composite liner considering load process was numerically calculated. The equivalence between GCL composite liner and CCL composite liner was evaluated. The scope of application of GCL composite liner was determined.