Long-Term Monitoring of a Tunnel in a Landslide Prone Area by Brillouin-Based Distributed Optical Fiber Sensors.

Aldo Minardo,Giuseppe Macchia,Luciano Picarelli,Caterina Di Maio,Giovanni Zeni,Ester Catalano,Agnese Coscetta,Luigi Zeni,Roberto Coviello,Roberto Vassallo

doi:10.3390/s21217032

Abstract

This paper shows the results of the monitoring of the deformations of a tunnel, carried out using a distributed optical fiber strain sensor based on stimulated Brillouin scattering. The artificial tunnel of the national railway crosses the accumulation zone of an active landslide, the Varco d’Izzo earthflow, in the southern Italian Apennines. Severely damaged by the landslide movements, the tunnel was demolished and rebuilt in 1992 as a reinforced concrete box flanked by two deep sheet pile walls. In order to detect the onset of potentially dangerous strains of the tunnel structure and follow their time trend, the internal deformations of the tunnel are also monitored by a distributed fiber-optic strain sensor since 2016. The results of the monitoring activity show that the deformation profiles are characterized by strain peaks in correspondence of the structural joints. Furthermore, the elongation of the fiber strands crossing the joints is consistent with the data derived by other measurement systems. Experiments revealed an increase in the time rate of the fiber deformation in the first and last part of the monitoring period when the inclinometers of the area also recorded an acceleration in the landslide movements.

Highlights

In the last decades, there has been a growing interest in the use of distributed optical fiber sensors in the field of structural and geotechnical engineering
Distributed optical fiber sensors are usually based on some form of scattering of the light propagating in the fiber, Raman scattering, Rayleigh scattering, and Brillouin scattering
Distributed optical fiber sensors based on Brillouin scattering feature extremely long sensing distances; they are typically preferred for the monitoring of large structures from remote locations [4,5,6]

Summary

Introduction

There has been a growing interest in the use of distributed optical fiber sensors in the field of structural and geotechnical engineering. These sensors offer the unique advantage of detecting the strain distribution over an extended area and at high spatial resolution [1,2,3]. They share the advantages of optical fiber sensors, such as small size, light weight, corrosion resistance, ease of encapsulation and implementation. It was found that the discrepancy of the strains measured by the optical fiber sensor and by a conventional strain gauge was very limited

Results

Discussion

Conclusion