Numerical Simulation of Synergistic Groundwater Dynamics and MultiStage Landslides on the Loess Tableland Margin with Implications for Geomorphic Evolution

Groundwater dynamics along loess tableland margins strongly interact with multi-stage landslides, yet their quantitative feedback mechanisms remain poorly understood. Typical loess multi-stage landslides in the southern Jingyang-Tableland are investigated by combining the finite element method (FEM) and finite-discrete element method (FDEM). FEM was used to characterize slope seepage and stability and to delineate critical slip surfaces, whereas FDEM simulated post-failure runout. The seepage field, pore water pressure, slope safety factor, shear strain distribution, and landslide movement and accumulation were quantitatively characterized. Results indicate that irrigation-induced groundwater rise progressively reduces the safety factor and drives slopes toward instability. Landslide deposits reshape slope boundary and seepage conditions, induce localized backwater effects, and, with sustained irrigation recharge, favor subsequent failures. Constrained by pre-existing deposits, the shear strain concentration zone of later landslides shifts upward from the slope toe to the midupper slope, with uplift of the shear outlet and reduced runout and scale, ultimately forming an imbricated accumulation structure. Repeated landsliding gentles topographic gradients and stabilizes seepage, driving the slope system toward a balancedgeomorphic state. This study quantifies the synergistic evolution and controls of irrigation-induced groundwater rise and multi-stage landslides, providing a basis for disaster mitigation and farmland conservation in loess tableland areas.