Mechanism of seepage-driven in situ improvement of dispersive soils in earth-rockfill dam clay cores using a lime filter layer

Dispersive soils used in earth-rockfill dam clay cores are highly susceptible to internal erosion, while conventional mechanical mixing methods suffer from limitations in achieving uniform improvement. To address these issues, a seepage-driven in situ improvement method employing a lime filter layer was proposed. Laboratory seepage tests were conducted to investigate the effects of lime filter layer thickness, hydraulic gradient, and seepage duration on the improvement performance of dispersive soils. The results indicate that the thickness of the lime filter layer is the primary factor governing the improvement performance. Under the experimental conditions investigated, the original dispersive soil was successfully transformed into non-dispersive soil when the lime filter layer thickness was 15 mm, the hydraulic gradient was 3.75, and the seepage duration was 5 d, corresponding to the best overall improvement performance. Microscopic analyses revealed that seepage promoted the migration of Ca 2 ⁺ into the soil, inducing Na⁺/Ca 2 ⁺ ion exchange, diffuse double-layer compression, and particle rearrangement, thereby driving the pore structure to evolve from a loose to a denser state. After treatment, the mass fraction of Na decreased from 3.84% to 1.01%, while the porosity decreased from 21.60% to 5.94%.The proposed method adopts a non-contact in situ improvement approach and shows potential for integration with clay core construction practices, providing an experimental basis for the in situ treatment of dispersive soils in earth-rockfill dam clay cores.