Influence of salt concentration on the shear strength of loess under rate effects

Field observations at the toes of loess landslides show seepage outlets, preferential flow paths, salt efflorescence, soils with high water content, and indurated crusts or blocks formed by salt precipitation, which may locally increase resistance to movement. To examine how salinity affects loess shear strength at different shear rates, ARS ring shear tests were conducted on Heifangtai loess with different salt concentrations and shear rates, combined with SEM characterization. The results show that: (1) shear strength first increases and then decreases with salinity, reaching a maximum at 8%; above this concentration, strength decreases and brittle behavior becomes more pronounced. Vertical settlement indicates shear-induced contraction. (2) Residual strength decreases with increasing shear rate, indicating a negative rate effect. The absolute value of the rate effect coefficient first decreases and then increases, with the strongest rate dependence at 20% salinity. (3) Low to moderate salinity promotes salt bridge cementation, flocculation, and dense fine aggregates, whereas high salinity induces salt coatings, particle breakage, poor contact quality, and connected pore networks, thereby reducing strength. (4) Higher salinity decreases zeta potential and electrokinetic mobility, compressing the electrical double layer and enhancing particle flocculation. These findings clarify the coupled salinity and rate effects on loess strength.