**Gerd Manthei 1,\* and Katrin Plenkers <sup>2</sup>**


Received: 31 July 2018; Accepted: 24 August 2018; Published: 9 September 2018

**Featured Application: This article describes various applications of in situ acoustic emission (AE) monitoring in the context of structural health monitoring (SHM) in mines and extensively presents the state of the art in this field.**

**Abstract:** A major task in mines and even more in underground repositories for nuclear waste is to investigate crack formation for evaluation of rock mass integrity of the host rock. Therefore, in situ acoustic emission (AE) monitoring are carried out in mines as part of geomechanical investigations regarding the stability of underground cavities and the integrity of the rock mass. In this work, the capability of in situ AE monitoring in the context of structural health monitoring (SHM) in mines and in various geological settings will be reported. SHM pointed out, that the AE network is able to monitoring AE activity in rock with a volume up to 10<sup>6</sup> cubicmeter and distances up to 200 m (e.g., 100 m × 100 m × 100 m) in the frequency range of 1 kHz to 150 kHz. Very small AE events with source size in approximately centimeter to millimeter scale are detected. The results show that AE activity monitors rock deformation in geological boundaries due to convergence of the rock. In addition, high AE activity occurs in zones of dilatancy stress in homogenous rock. In conclusion in situ AE monitoring is a useful tool to observe instabilities in rock long before any damage becomes visible.

**Keywords:** in situ acoustic emission (AE) monitoring; structural health monitoring; mines; host rock
