With the strategic westward shift of China’s infrastructure development, the western mountainous regions have become the focal point for large-scale tunnel and underground engineering construction. However, these regions are characterized by highly complex geological structures and abundant groundwater reserves, exposing underground projects to water-induced hazards. Rocks of different lithologies exhibit noticeable behavioral differences under water-induced degradation. Argillaceous slate is particularly susceptible to water; thus, its progressive failure mechanical properties and damage evolution laws urgently require systematic investigation. To address this, uniaxial compression tests coupled with synchronous full-process acoustic emission (AE) monitoring were conducted on argillaceous slate specimens under varying water-bearing states. This study reveals the mechanical response characteristics and spatiotemporal evolution laws of AE in argillaceous slate, summarizing the distinctive patterns in rock failure processes across different water-bearing conditions.

(1) The compressive strength of the argillaceous slate specimens decreased from 62.7 MPa in the dry state to 34.25 MPa in the water-saturated state, representing a reduction of 45.37%. Similarly, the elastic modulus declined from 12.29 GPa in the dry state to 9.35 GPa in the saturated state, corresponding to a decrease of 23.9%. (2) Following water saturation, the crack damage stress level of the argillaceous slate specimens decreased by 15%. Compared with the dry state, the elastic strain energy of the specimens in the water-saturated state dropped significantly by 67%. (3) The cumulative AE ring-down count of the specimens decreased from 1.6 × 10⁴ in the dry state to 1.2 × 10⁴ in the saturated state, representing a 25% reduction. The cumulative AE energy plummeted from 142.76 × 10^-18 J in the dry state to 22.01 × 10^-18 J in the saturated state, amounting to an 84.6% decrease. (4) For the specimens in the dry state, the dominant frequency exhibited notable sudden drops around 200 and 400 s of loading. Meanwhile, after 300 s, the dominant frequency signals of the specimens in the water-saturated state were relatively evenly distributed within the 100–400 kHz frequency band. The proportion of low-amplitude signals for both states accounted for approximately 80%. Additionally, compared with the dry state, AE events during the initial loading stage were extremely sparse for the specimens in the water-saturated state. The tensile-shear microcracking mechanism of the argillaceous slate specimens was primarily characterized by a combination of high AF values and low RA values. The RA values of the saturated specimens exhibited significant increases in quantity and absolute magnitude.

(1) Argillaceous slate specimens undergo multiple localized fracturing during the yield stage. Such phased sudden increases in circumferential strain act as a key precursor to the macroscopic failure of the rock. Quantitatively, the instability precursor is defined as the point at which the circumferential strain rate reaches 10 times the axial strain rate. (2) Water saturation significantly weakens the localized multiple fracturing phenomenon and its associated failure precursors in argillaceous slate. Consequently, the failure process lacks the large-scale, abrupt damage observed in the dry state. (3) AE signal characteristics further reveal the weakening and transitional mechanisms induced by water on the failure mode of argillaceous slate. Unlike specimens in the dry state, which exhibited sudden drops in the AE’s b-value and dominant frequency due to internal crack activation, specimens in the water-saturated state displayed a more uniform dominant frequency distribution, indicating a more gradual and stable overall failure process. (4) The significantly increase in RA values in the water-saturated state indicates an alteration in the microcracking mode induced by water, which further suppresses the abrupt propagation of localized tensile cracks and leads to a more ductile instability and failure behavior.