Nano-Enhanced Electrokinetic Conditioning of Expansive Soils

Abstract

This study presents a combined experimental and numerical investigation into the stabilization of expansive soils using magnesium oxide (MgO) nanoparticles and electrokinetic (EK) treatment. The research was conducted in three phases to evaluate the individual and coupled effects of nanoconditioning and electrokinetics on the hydro-mechanical behavior of expansive soils. Initial laboratory testing compared MgO and SiO2 nanoparticles at different concentrations. MgO nanoparticles demonstrated superior performance, with 3% MgO increasing the plastic limit by 43.25%, reducing the plasticity index by 22.78%, and nearly eliminating vertical swell strain. In contrast, SiO2 nanoparticles showed comparatively limited improvement and less consistent behavior. The second phase evaluated EK treatment under applied voltages of 10, 15, and 25 V. Improvements in soil properties were observed, including an increase in unconfined compressive strength to 175.43 kPa near the anode at 25 V, representing a 190.93% increase compared to untreated soil. The combined EK–MgO treatment produced the greatest improvement, achieving a 28.26% reduction in swell strain and a 221.39% increase in compressive strength. X-ray fluorescence analysis confirmed MgO nanoparticle distribution within the soil matrix. To complement the experimental investigation, a two-dimensional multiphysics finite element model was developed in COMSOL Multiphysics to simulate electroosmotic flow, nanoparticle transport, and electric field behavior. The model incorporated the modified Navier–Stokes, Nernst–Planck, and Helmholtz–Smoluchowski equations and successfully reproduced the experimentally observed nanoparticle migration and aggregation patterns. Overall, the findings demonstrate that combining electrokinetics with MgO nanoparticle conditioning provides an effective and non-destructive approach for expansive soil stabilization and offers a reliable framework for optimizing treatment performance in geotechnical applications.