Abstract:

To investigate the superposition effect of three-dimensional compressive stress on the longitudinal wave velocity of rocks and improve the testing precision of the rock mass integrity index, this study takes sandstone-like materials as the research object and measures the evolution law of axial and transverse longitudinal wave velocities in specimens under compressive stress. The internal crack evolution process is qualitatively characterized by the crack volume strain, revealing the physical essence of the longitudinal wave velocity variations. Based on the principles of the acoustic-elastic effect, a correction model for the longitudinal wave velocity of rock blocks under the coupling effect of three-dimensional principal stresses is established, and a method for correcting the rock mass integrity index under the condition of a corrected three-dimensional in-situ stress field is obtained. The results indicate that the evolution of the longitudinal wave velocity, measured both axially and transversely, corresponds to the four distinct stages of rock mass failure. The corresponding variations in the longitudinal wave velocity across different stages can be attributed to three primary factors: micro-crack closure and initiation altering wave propagation paths, rock mass compaction enhancing stiffness, and the marked anisotropy of newly generated micro-cracks. The proposed correction model for the longitudinal wave velocity and the associated method for revising the rock mass integrity index demonstrate broad engineering applicability. This approach significantly enhances the measurement precision of the rock mass integrity index, thereby facilitating a more refined classification of rock mass quality.

Key words: rock mass, in-situ stress, longitudinal wave velocity, rock mass integrity index, acoustic-elastic effect