Earthquake-induced loess landslides often exhibit extraordinarily long runout distances despite originating from gently slopes, posing significant challenges for hazard assessment and disaster mitigation. Existing studies generally investigate liquefaction initiation and post-failure mobility independently, leaving the continuous physics processes governing catastrophic failure insufficiently understood. This study proposes an integrated hydro-mechanical-rheological framework to elucidate the complete evolution from liquefaction initiation to landslide motion.
      The study is based on the 2023 Zhongchuan co-seismic loess landslide triggered by the Ms 6.2 Jishishan earthquake in northwestern China. A series of dynamic back-pressure direct shear tests, undrained ring-shear tests, and rheological experiments were conducted to investigate the coupled evolution of pore-water pressure, shear resistance, shear rate, and viscosity during seismic loading. The effects of initial pore-water pressure, cyclic loading frequency, loading amplitude, and initial shear stress on liquefaction initiation and subsequent mobility were systematically evaluated.
      Experimental results demonstrate that elevated initial pore-water pressure lowers the liquefaction threshold by accelerating excess pore-water pressure accumulation and effective stress reduction. Dynamic loading further promotes pore collapse and rapid strength degradation, leading to liquefaction once a critical pore-water pressure state is reached. Following liquefaction, the saturated loess exhibits pronounced shear-thinning behavior, with viscosity decreasing continuously as shear rate increases. This rheological weakening establishes a positive feedback mechanism in which increasing flow velocity further reduces viscosity, thereby sustaining high-mobility motion.
      The proposed multiphysics framework explicitly links seismic loading, hydro-mechanical coupling, and post-failure rheology into a unified failure process. These findings improve the physical understanding of earthquake-induced loess landslides and provide useful insights for hazard assessment and risk reduction of geohazards.
 

landslide,earthquake,loess,test,porewaterpressure