Hydro-mechanical behavior of bentonite under the erosion of alkaline solution and its prediction model

Abstract

Bentonite is widely employed in landfill liners for hazardous waste containment owing to its strong adsorptive and swelling capacity. However, alkaline industrial effluents can induce significant degradation, impairing its hydraulic performance. This study investigates the influence of NaOH solutions on the swelling and permeability of bentonite through swelling and consolidation tests. Results indicate that elevated alkalinity reduces the swelling rate and increases the permeability coefficient. XRD analyses confirm a progressive decrease in montmorillonite content with increasing NaOH concentration, which directly explains the loss of swelling ability. SEM observations reveal that alkaline conditions cause montmorillonite particles to fragment and aggregate into clusters, forming larger inter-aggregate seepage channels. MIP data further corroborate a shift in pore size distribution from small to larger pores, facilitating more permeable pathways. The swelling behavior was modeled using an e–p_e fractal approach, where e is the void ratio and p_e denotes effective stress incorporating osmotic suction. Fitted parameters show that the swelling coefficient η decreases with montmorillonite content, while the fractal dimension D_s increases due to microstructural coarsening. By incorporating the number of montmorillonite layers (n_s), the permeability–void ratio relationship was refined. A predictive model for permeability under external load was developed and validated against experimental data. This work clarifies the microstructural evolution of bentonite under alkaline attack and provides a theoretical basis for predicting its long-term engineering performance.