Research on the Microscopic and Hydraulic Characteristics of Bentonite Modified Loess under Drying-Wetting Cycles Effect

Bentonite modified loess has the potential to serve as a clay liner layer in landfills, but the drying-wetting cycles can cause changes in the permeability and mechanical properties of the bentonite modified loess cushion layer, leading to leakage or instability damage in landfills, posing a threat to the long-term stability of the modified loess cushion layer. Taking plain loess and bentonite modified loess as research objects, experiments were conducted under different drying-wetting cycles, including scanning electron microscopy, mercury intrusion, flexible wall permeability, and uniaxial compression. The effects of dry-wet cycles on the microstructure, anti-seepage performance, and mechanical properties of modified loess were comprehensively analyzed at macro, micro, and nano scales, and the deterioration mechanism of modified loess under drying-wetting cycles was explored. The results show that: Bentonite can be used for loess solidification mainly due to the filling effect and water absorption and expansion characteristics of montmorillonite particles. The pore distribution of plain loess under different drying-wetting cycles is a three peak pore structure, while the pore distribution of modified loess is a bimodal pore structure; The permeability coefficient of plain loess continues to increase with the increase of drying-wetting cycles, while the permeability coefficient of modified loess tends to stabilize after five drying-wetting cycles; The uniaxial compression strength of both plain loess and bentonite modified loess tend to reach a stable value after five dry-wet cycles. Under different drying-wetting cycles, the uniaxial compressive strength of modified loess is higher than that of plain loess.