Application of a type of strain block FBG sensor for strain measurements of squeezing rock in a deep-buried tunnel

Abstract

Tunneling in squeezing rock often encounters large deformation, which threatens the safety and stability of tunnel support during tunnel construction. In this work, to acquire a greater amount of strain sensor data to fully understand the stress/strain state of surrounding rock during tunnel excavation, a special type of strain block with fiber Bragg grating (FBG) sensors has been introduced, which is characterized by three groups of FBG strain rosettes adhered to three adjacent surfaces of the block, respectively, and each strain rosette distributed in the form of a 0°–45°–90° arrangement. Applying this type of FBG strain block sensor to a deep-buried tunnel in squeezing rock, six strain components in one strain block (representative of strain state of a point in rock) could be obtained with the processing method. The monitoring results can reflect the effect of tunnel excavation due to abrupt changes of strain monitored in rock, and were verified as being in reasonable agreement with numerical simulation. Therefore, the strain block with FBG sensors can be applicable in measuring strains in squeezing rock.

Building a low-cost strain sensor prototype using fiber Bragg gratings with resonant cavity light emitting diodes

“…The interrogation scheme varies by application, but generally includes an optical source and a mechanism for detecting spectral shifts in the reflected light. To increase the SNR or to track multiple quantities simultaneously, it is common to have an array of FBGs in a single sensing matrix [1,4,5]. Most FBG sensors quantify the spectral shift of the reflected light using multiplexors with multiple photodiodes [1], an optical spectrum analyzer, or a spectrometer [1,5].…”

“…To increase the SNR or to track multiple quantities simultaneously, it is common to have an array of FBGs in a single sensing matrix [1,4,5]. Most FBG sensors quantify the spectral shift of the reflected light using multiplexors with multiple photodiodes [1], an optical spectrum analyzer, or a spectrometer [1,5]. While each of these methods carries advantages, each can also add significantly to the overall cost and complexity of the sensor, which can limit the use of FBG sensors.…”

Analysis of Reliability of Strain Measurements Made with the Fiber Bragg Grating Sensor Rosettes Embedded in a Polymer Composite Material

“…The general solution to the problem of strain measurement by various sensors, including fiber-optic sensors, is associated with obtaining information about all components of the strain tensor. One way to solve this problem is to use special sensor layouts called rosettes [ 3 , 4 , 5 , 6 , 7 ]. When strain measurement is carried out inside or on the surface of a structure, being in the plane stress or plane strain state, the relevant information about all components of the strain tensor can be obtained using a rosette of three differently-directed sensors located on one plane.…”

A Fiber Bragg Grating Borehole Deformation Sensor for Stress Measurement in Coal Mine Rock

“…This inherent characteristic makes the FBG sensors very attractive for application in harsh environments [14], and long-term measurements using FBGs as sensing elements have been possible. FBG sensors are becoming more and more popular for geotechnical applications, and they are used to measure the strain [15,16], stress [17][18][19], displacement [20,21], and deformation [22][23][24] of the geotechnical media. In recent years, some unconventional FBG sensors, such as chirped FBG sensors [25] and tilted FBG sensors [26], are also proposed, and they show some advantages over traditional FBG sensors in some aspects.…”