Confinement and granular cohesion govern self-propelled intruder ascent

Self-propelled ascent in wet granular media remains poorly understood because cohesion, local fluidization, and geometric confinement are strongly coupled. Existing studies have mainly considered self-propelled intruders in dry granular beds or passive segregation under externally imposed flow. The central contribution of this work is an active-region framework that links liquid-bridge cohesion and finite-width confinement to local granular flow and intruder mobility. Experiments and calibrated discrete element simulations of a self-propelled spherical intruder reveal an initial quasi-static rising regime followed by a dynamic regime. Hydrostatic loading and liquid-bridge cohesion dominate the former, whereas developed local fluidization and inertial effects govern the latter. Wet cohesion stabilizes the particle network and suppresses the formation and expansion of the dynamically active region, thereby reducing the rising velocity. Narrow containers similarly restrict lateral grain rearrangement through wall-mediated force-chain transmission, while this confinement effect becomes negligible beyond a critical width. Variation of the intruder-to-particle size ratio reveals a non-monotonic response and a driving-dependent critical size ratio, R c . Below R c , increasing the size ratio expands the active region and accelerates ascent; above R c , the active-region extent approaches saturation and geometric confinement inhibits further ascent. Incorporating this crossover into an inertial-number relation yields a size-corrected scaling law for the rising velocity. These results provide a unified mechanistic and quantitative description of how cohesion and confinement regulate self-propelled transport through granular media.