Numerical Simulation of Tortuosity Effect on the Montmorillonite Permeability

Abstract

This study analyzed the association between the coefficient of permeability of clayey sealing materials and their tortuosity. Montmorillonite was selected because it is used as a barrier in geo-environmental projects and its sensitive structure results in wide variations in permeability when in contact with pore fluids. A DEM code was developed by considering mechanical force, diffuse double layer repulsion, and Van der Waals attraction as the inter-particle interaction. The coefficient of permeability was calculated by simulating a consolidation test and the DEM simulations were compared with experimental data. The results showed that the coefficient of permeability decreased as the void ratio decreased. At the same void ratio, there was a deviation between the coefficient of permeability for clay-electrolyte systems caused by the micro-fabric and variations in tortuosity. Micro-fabric evolution during loading showed that increasing the stress state caused reorientation of the particles perpendicular to the direction of loading and increased anisotropy of the particle orientation, increasing the tortuous flow path.

Leaching characteristics of metals from recycled concrete aggregates (RCA) and reclaimed asphalt pavements (RAP)

“… Mineralogy X-ray diffraction [ 30 ] Samples were analysed using PANatycalX’Pert diffractometer. Standard leaching Leaching characteristic of building material [ 27 ] L/S = 100 mL/g, pH = 4, particle size ≤2 mm and contact time = 48h Leaching tests as a function of L/S Compliance test for leaching of granular waste materials and sludge [ 31 ] L/S values ranging from 0.1 mL/g to 100 mL/g were tested for particle size < 4 mm while maintaining other factors constant (pH = 7 and contact time = 48h) Leaching tests as a function of pH Leaching behaviour test with initial acid/base addition [ 32 ] pH values ranging from 2 to 12 were tested while maintaining other factors constant (L/S = 10 mL/g, particle size <1 mm, contact time = 48h) Leaching tests as a function of compaction Compliance test for leaching [ 31 ] and compacted bulk density [ 33 ] 1.5 kg of dry material mixed with 13 % of water was compacted into each cylinder (70 mm diameter and 250 mm height) by applying different number of blows. The different compactions were achieved different number of blows (L/S = 10 mL/g, pH = 7, grain size <4 mm) Leaching tests as a function of DOC/TOC Compliance test for leaching [ 31 ] and method 5310C [ 34 ] Tests were carried out with five different concentrations of DOC/TOC in leachate by maintaining other factors constant (L/S = 10 mL/g, pH = 7, particle size <4 mm and contact time = 48h) …”

“…For example, percolation is one of the key physical processes that influence pollutant leaching while factors such as porosity and particle size of granular aggregates exert a significant influence on the percolation ability [ 25 , 26 ]. Diffusion, porosity and tortuosity significantly affect the movement of pollutants with leachate and are influenced also by compaction and particle size of the material [ 24 , 27 ]. In terms of chemical factors, dissolution, carbonation and acid/base buffering are three key factors influencing the pollutant leaching.…”