Nondestructive Velocity Structure Reconstruction for Complex Rock Mass Using 3-D Acoustic Emission Tomography

Acoustic emission (AE) technology combined with acoustic tomography can realize the early detection for unknown velocity structure of rock mass. However, multifactors limit the resolution of tomography in complex rock mass. To meet the high-efficiency and high-resolution requirements of unknown structure detection in underground engineering, this article develops a 3-D AE tomography (AET) method using velocity-free source location method (VFL) and time-difference adjoint tomography (TDAT). The proposed method adopts independent rather than alternate location and tomography system. The VFL is utilized to determine the position of AE sources without velocity measurement. The adjoint state system is introduced in TDAT to avoid ray tracing. Furthermore, the quasi-Newton method is adopted to iteratively update the velocity model. The proposed AET reduces the strict demand on prior model and possesses outstanding inversion efficiency. Numerical and laboratory experiments were conducted to verify the effectiveness and feasibility. The results show that the proposed method can accurately estimate the position of AE sources and exactly reconstruct the velocity anomaly and damage buried in complex rock mass. It not only realizes the nondestructive velocity structure reconstruction of complex rock mass using AE events but also provides new insight for other AE testing application fields.