Monitoring of Rocks and Underground Structures Using PZT and FBG Sensors

Abstract

This chapter discusses the feasibility of employing the new generation fiber optic and piezoelectric sensor systems for comprehensive monitoring of rocks, covering load history monitoring/retrieval as well as damage assessment. In several major cities across the world, city planners are paying serious attention to the development of usable underground space in the form of caverns and tunnels due to continuously depleting land availability (Zhao et al., 1999). In addition, underground structures are considered safer compared to surface structures against earthquakes and hurricanes, and are less prone to noise pollution (Goel, 2001). However, they demand huge resources for construction and maintenance, and any collapse could be detrimental to the nation’s economy in terms of lives and properties. This necessitates their comprehensive monitoring on a regular basis to check the onset of damages. Damages might occur due to environment-induced degradation, fatigue, excessive/unpredicted loads, and underground blasts. In addition, instrumentation and monitoring of the underground structures during construction and operation can facilitate validation of key design assumptions. This is especially pertinent to the underground structures, since quite often, many geotechnical and environmental complexities cannot be accurately considered at the design stage. Comprehensive instrumentation can pave the way for long-term monitoring of external loads, stress distributions and deflections, which can be useful for comparing the predicted and the actual responses as well as detecting the occurrence of structural damage in real-time, thereby ensuring a high level of safety. In addition, the database generated could economize future constructions.