Abstract: Underground deep engineering projects, particularly in large water-rich mines or under water-rich mining conditions, are significantly affected by groundwater infiltration, which compromises the stability of engineering rock masses. To reveal the crack evolution characteristics and rockburst tendency of sandstone under different immersion depths, uniaxial compression tests, acoustic emission (AE) monitoring, and scanning electron microscope analysis were conducted on sandstone samples subjected to six immersion depths: 0, 20, 40, 60, 80, and 100 mm. The results indicate the following trends: 1) With increasing immersion depth, both the elastic modulus and compressive strength of the samples deteriorate to varying degrees, with the most significant reduction occurring in the 0–20 mm immersion depth range. 2) With increasing immersion depth, high-frequency AE signals gradually increase, accompanied by a rise in small-scale fractures. The cumulative energy of low-frequency AE decreases significantly, from 747 980.30 to 31 084.71 mV·ms, indicating a gradual reduction in fracture scale. The AE r value at the critical failure point decreases from 1.84 to 1.14, reflecting a lower energy concentration and a transition toward static failure modes. 3) With increasing immersion depth, the number of cracks in failed samples increases, whereas the energy associated with AE localization points decreases. At 100 mm immersion depth, the energy concentrates primarily in the range of 16.4–32.8 mV·ms, with large-scale fractures diminishing and small-scale fractures becoming more prevalent. 4) By integrating elastic strain energy, energy dissipation during failure, and failure duration, a new criterion for rockburst tendency—the residual energy release rate index ( W_T )—is proposed. Using both the index W_T  and the elastic-impact comprehensive energy index ( X_E ), the rockburst tendency of sandstone samples under different immersion depths is classified as weak rockburst, with the index values gradually decreasing as immersion depth increases. The weak rockburst category is further subdivided into three subclasses: weak rockburst-high tendency, weak rockburst-medium tendency and weak rockburst-low tendency. 5) Under different immersion depths, the failure cracks are characterized as tensile-shear composite cracks, and the failure mode transitions from shear failure to tensile-shear composite failure. A multi-scale instability model for immersed sandstone is established, revealing the micro-meso-macro instability mechanism of sandstone under hydraulic coupling: water-rock interactions lead to the dissolution of mineral particles and clay minerals, as well as the generation of microcracks. Under loading, these microcracks propagate, connect, and fracture, ultimately forming macroscopic cracks that result in sample instability and failure. These findings provide insights for evaluating the stability of engineering rock masses affected by immersion depth and for predicting rockburst occurrences.

Key words: immersion depth, sandstone, crack evolution, acoustic emission, rock burst tendency