Fiber-Optic Underground Sensor Networks: Distributed Fiber-Optic Strain Sensing for Monitoring Underground Structures - Tunnels Case Studies

The main motives driving the trend toward increased implementation of structural monitoring systems are the need for structural health monitoring of existing and ageing structures and the desire for a better understanding of increasingly complex designs through performance monitoring of new structures. This drive is sustained by rapid progress in research and technology development on sensors and communications.This chapter presents three case studies focusing on the monitoring of tunnels using distributed fiber-optic sensing. The first case study presents the results of strain development in the sprayed concrete lining (SCL) of a new Crossrail station tunnel during excavation of a cross-passage. The second case study focuses on the short term monitoring of a century old cast iron tunnel during the proximity construction of a large platform tunnel for the Crossrail project. The final case study describes the early stage implementation of a long-term structural health monitoring program to assess the integrity of tunnels at CERN. For all these projects Brillouin-based time domain techniques were used. A brief description of the basic principles of the method and the fiber-optic systems used is presented before the case studies.The variety of optical fibers available today combined with the number of fibre devices, with improved characteristics, recently developed provides a countless potential sensor configurations for environmental monitoring. In this chapter, a background of the use of fiber optic sensor networks in environmental applications are discussed focus in the optical detection for gas leakage sensing, water contamination sensing, soil contamination sensing and mapping with distributed fiber-optic sensors for environment.