Effect of granule size on intergranular pores and hydraulic conductivity of granular bentonite in geosynthetic clay liners

Effect of granule size on swelling behavior, intergranular pores, and hydraulic conductivity was evaluated experimentally for thin granular sodium bentonite layers used in geosynthetic clay liners (GCLs). Five granule size intervals were evaluated, ranging from fine to coarse: 0.075–0.25, 0.25–0.50, 0.50–1.0, 1.0–1.05, and 1.05–1.40 mm. Granule swelling, column swelling, and hydraulic conductivity tests were conducted using deionized water (DIW), 100 mmol/L NaCl, and 100 mmol/L CaCl 2 to induce high, moderate, and low swelling. Swollen granule size correlated linearly with dry size, with swelling ratios (swollen radius ÷ dry radius) of 1.9 (DIW), 1.3 (NaCl), and 1.2 (CaCl 2 ). Column swelling ratios (swollen height ÷ dry height) showed similar trends: 3.2 (DIW), 1.5 (NaCl), and 1.2 (CaCl 2 ). Hydration and intergranular pore-size characteristics varied with granule size: fine granules hydrated more slowly, forming finer, more uniform, and dispersed pores; coarse granules hydrated faster with larger, preferentially connected pores. Granule size had little effect on hydraulic conductivity in DIW (∼10 −11 m/s), but with NaCl and CaCl 2 , conductivity increased up to five orders of magnitude from fine to coarse granules. Microscopy revealed minimal intergranular pores in DIW, while larger, more interconnected pores were obtained with NaCl and CaCl 2 (31–564 µm in NaCl, 67–1122 µm in CaCl 2 ).