Effect of confining pressure on mechanical behavior and acoustic emission characteristics of rock masses with different dissolution degrees

To reveal the mechanical behavior, acoustic emission response and failure mechanism of rock masses with different dissolution degrees under confining pressure, rock-like specimens with dissolution degrees of 0%, 5%, 10%, 15% and 20% were prepared using the pre-embedded ice ball melting method. Conventional triaxial compression tests coupled with AE monitoring were conducted to systematically investigate the effects of confining pressure and dissolution degree on mechanical parameters, AE ring counts, RA-AF characteristics, b value, energy release, peak frequency and macroscopic failure morphology. The results show that: (1) Increasing confining pressure significantly enhances specimen strength and deformation resistance. When the confining pressure increased from 3 MPa to 12 MPa, the peak strength increased by 22.85%~33.90%, the elastic modulus increased by 18.88%–37.88%, and the deformation modulus increased by 24.83%–30.48%. In contrast, increasing dissolution degree weakened the effective load-bearing skeleton and structural continuity. At 3 MPa, the peak strength decreased by 26.51% as the dissolution degree increased from 0% to 20%, while the corresponding reduction reached 31.71% at 12 MPa. (2) AE ring counts become markedly active after the crack propagation stage and further increase near the peak and in the post peak stage. Increasing confining pressure transforms AE activity from concentrated and abrupt release to continuous and progressive release, whereas increasing dissolution degree lowers the crack initiation threshold, activates AE activity earlier and significantly widens the pre-peak damage accumulation interval. (3) Tensile cracks and shear cracks develop simultaneously during specimen failure, indicating a tensile shear failure mode. Increasing confining pressure promotes the transition of cracking mode from tensile cracking to shear sliding, whereas increasing dissolution degree enhances local tensile stress concentration around cavity boundaries and increases the proportion of tensile cracks. (4) The damage process is accompanied by the transition from small scale microcracking to large scale coalescence failure, and dissolution defects accelerate this crack scale transition. The macroscopic failure morphology shows that intact and low dissolution specimens are dominated by overall shear failure, whereas high dissolution specimens gradually transform into defect controlled tensile shear failure. These findings provide experimental evidence for evaluating the stability and early warning characteristics of karst tunnel surrounding rock affected by dissolution defects.”