Landslides often exhibit step-like non-uniform deformation under external factors such as rainfall and reservoir water level fluctuation. The soils in sliding zone experience non-uniform shear cycles involving deceleration and acceleration, where their shear strength may act as a variable rather than a constant. Taking the Baijiabao landslide slip zone soil as an example, a series of multi-stage ring shear tests with stepwise acceleration and deceleration rates are conducted. The shear surfaces under varying rate are macroscopically analyzed using a 3D surface topography measurement system to investigate the changes of the residual shear strength under non-uniform shear conditions. The results demonstrate that the residual strength of the soils in sliding zone exhibits a decreasing trend, showing a relative reduction of 3.0% to 24.1% under stepwise acceleration shearing with rates ranging from 0.3 to 9.9 mm/min. Conversely, under stepwise decelerated shearing, the residual strength increases by 2.9% to 34.6%. The accelerated shearing progressively deepens scratch marks on the shear surface, while the decelerated shearing tends to be smooth and reorganize these scratches into more ordered configurations. Furthermore, the comprehen-sive internal friction angle (φₑ) of the soils in sliding zone displays a logarithmic decay relationship with the shear rate (v), which is quantitatively described by the equation  φ_e=-1.56ln(v+0.15)+22.1. These findings systematically elucidate the evolution of residual strength of the soils in sliding zone under non-uniform shear deformation, providing critical insights for refining landslide stability assessments and enhancing early-warning systems.
 

landslide shear strength,ring shear test,slow deformation