Failure characteristics and mechanisms of uniaxial compressed red sandstone in non-uniform water distribution environment: Effects of immersion height and duration

• Peak strength and elastic modulus of red sandstone are highly sensitive to immersion height, with reductions of 38% and 23% even at L=1/50H. • Water immersion reduces both energy storage and dissipation capabilities of red sandstone. • Immersion height and duration control the migration and separation of dry-wet interfaces, influencing failure modes. • Low immersion heights pose significant risks to underground rock structures, with the concentration degree of water non-uniform distribution being a key factor in assessing water-induced weakening.