This paper explores the possibility of using the electro-mechanical impedance (EMI) technique for structural health monitoring (SHM) of underground rock structures. The underground structures are complex in design and require continuous inspection for their maintenance. However, some of the underground areas are inaccessible for the inspection team or might warrant a special clearing arrangement, leaving the structure out of service. The complexity in their design, their construction, and the conditions encountered during service life necessitate the deployment of a dedicated SHM system. Sometimes the stress ratio in rock because of overburden stress and tectonic activities may reach a high value exceeding threshold, which may lead to rock bursts and subsequent failure of the structure. The SHM technique becomes important for underground infrastructure to enable timely detection of the damage caused by any anticipated or unanticipated loads. In the present study, rock specimens have been tested in a laboratory environment under saturated, as well as dry, conditions, under pre-loaded stress conditions by applying continuous quasi-static loading, so as to simulate the near-real-life underground conditions. The EMI technique is used for damage monitoring. The vibrations generated by the actuation of lead zirconate titanate (PZT) patch are sensed by the same PZT patch and recorded in the form of conductance and susceptance signatures. The signatures have been quantified using root-mean-square-deviation (RMSD) method. The test results clearly establish the potential of the EMI technique in detecting and quantifying load-induced damage in dry, as well as saturated, conditions in the underground structures, opening avenues for applications in real-life situations.
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