Membrane Efficiency and Diffusive Tortuosity of a Dense Prehydrated Geosynthetic Clay Liner

Authors

Michael A. Malusis, Bucknell UniversityFollow
Akmal S. Daniyarov, Parsons BrinckerhoffFollow

Publication Date

Summer 6-1-2016

Description

In this study, a series of membrane/diffusion tests were conducted on specimens of a dense prehydrated geosynthetic clay liner (DPH GCL) subjected to KCl solutions (source concentration, C_o = 8.7-160 mM) in rigid-wall cells. The source KCl solutions and de-ionized water (DIW) were circulated across the top and bottom specimen boundaries, respectively, and membrane efficiency coefficients, w, were measured based on the differential pressures induced across the specimens due to prevention of liquid flux. Also, effective salt-diffusion coefficients, D_s^*, and apparent tortuosity factors, t_a, were determined for each specimen based on the steady-state diffusive Cl^- flux measured at the exit (bottom) boundary. The DPH GCL specimens exhibited higher w and lower D_s^* (and, likewise, lower t_a) relative to conventional (granular, non-prehydrated) GCL specimens tested under similar conditions. The results were consistent with the lower hydraulic conductivities, k, measured for the DPH GCL specimens and are attributed primarily to the higher bentonite dry densities in the DPH GCL specimens (1.1 Mg/m³) relative to the conventional GCL specimens (~0.4 Mg/m³), although differences in bentonite texture (powdered versus granular), bentonite type (treated versus untreated), and testing apparatus (rigid wall versus flexible wall) may have been contributing factors. Both the DPH GCL and the conventional GCL exhibited similar trends of decreasing t_a with increasing w. The t_a values are considered to be a function of both a matrix tortuosity factor, t_m, that accounts for the geometry of the interconnected pores, and a restrictive tortuosity factor, t_r, that accounts for solute exclusion due to membrane behavior. Whereas the DPH GCL exhibited a lower t_m relative to the conventional GCL, both GCLs exhibited similar trends of decreasing t_r with increasing w. The relationship between t_r and w for both GCLs is reasonably well represented by t_r = 1 – w, an expression that has been proposed for clay membranes in previous theoretical and experimental studies.

Journal

Geotextiles and Geomembranes

Volume

44

First Page

719

Last Page

730

Department

Civil and Environmental Engineering

Link to Published Version

http://www.sciencedirect.com/science/article/pii/S0266114416300462

Recommended Citation

Malusis, M.A. and Daniyarov, A.S. (2016). Membrane efficiency and diffusive tortuosity of a dense prehydrated geosynthetic clay liner. Geotextiles and Geomembranes, 44, 719-730.