Open pit slope deformation monitoring by fiber Bragg grating sensors

Zhang

et al. 2018

Sensors

Fiber Bragg grating (FBG) measuring bolts, as a useful tool to evaluate the behaviors of steel bolts in underground engineering, can be manufactured by gluing the FBG sensors inside the grooves, which are usually symmetrical cuts along the steel bolt rod. The selection of the cut shape and the glue types could perceivably affect the final supporting strength of the bolts. Unfortunately, the impact of cut shape and glue type on bolting strength is not yet clear. In this study, based on direct tension tests, full tensile load–displacement curves of rock bolts with different groove shapes were obtained and analyzed. The effects of groove shape on the bolt strength were discussed, and the stress redistribution in the cross-section of a rock bolt with different grooves was simulated using ANSYS. The results indicated that the trapezoidal groove is best for manufacturing the FBG bolt due to its low reduction of supporting strength. Four types of glues commonly used for the FBG sensors were assessed by conducting tensile tests on the mechanical testing and simulation system and the static and dynamic optical interrogators system. Using linear regression analysis, the relationship between the reflected wavelength of FBG sensors and tensile load was obtained. Practical recommendations for glue selection in engineering practice are also provided.

Section: Introductionmentioning

confidence: 99%

Study on the Optimal Groove Shape and Glue Material for Fiber Bragg Grating Measuring Bolts

Zhang

et al. 2018

Sensors

“…where n eff is the effective refractive index of the grating in the fiber core and Λ is the grating period. 1,2,9,10,13,[15][16][17] The Bragg wavelength is very sensitive to external changes, such as strain or temperature variation, 1) so the sensing principle of an FBG sensor is based on the fact that both the effective refractive index of the grating and the grating period change when the strain or temperature changes, thus causing a shift in the wavelength of the reflected spectrum. It is possible to measure the changes in strain or temperature from the amount of Bragg wavelength shift.…”

Section: Sensing Principle Of An Fbg and Strain Measurement Methodsmentioning

confidence: 99%

“…These include small size, lightweight, possibility of remote sensing, immunity to electromagnetic interference, low loss, lack of need for electrical power, wide bandwidth, good corrosion resistance, and high sensitivity. [1][2][3][4][5][6][7][8][9][10] Moreover, FBG sensors have an excellent linear relationship with respect to temperature and strain. 2,11) Furthermore, the sensing technology of FBGs as strain and=or temperature sensors has been studied by researchers, and a number of survey papers with excellent results have been published.…”

Section: Introductionmentioning

confidence: 99%

Development of a low-cost and miniaturized fiber Bragg grating strain sensor system

Yuan

Sato

2017

Jpn. J. Appl. Phys.

A fiber Bragg grating (FBG) strain sensor system that measures strains from reflected power changes of FBGs is presented. A laser diode used as a light source and a power meter are used in the system, which makes the FBG sensor system inexpensive and miniaturized. The reflected power of an FBG is expressed by the product of the reflectivity of the FBG and the optical power of the laser diode. Comparison of the strain applied in the experiment with that calculated from the reflected power shows that relative errors are within 5.1%, which verifies the feasibility of the strain sensor system proposed in this work. In addition, on the basis of this method, we fabricate a cantilever load cell using an FBG as the strain gauge instead of an electrical resistance, and also quantify the load range that can be measured by this load cell.

“…At the same time, fiber optical sensing technologies have also been widely used in landslide monitoring due to their small size, high resolution, and in-site monitoring and multiplexing capabilities [11,12,13,14]. Previous studies have established that surface deformation [15,16], subsurface deformation [17,18,19,20], reinforcements [21,22,23,24,25], the strain field [26,27,28,29], soil pressure [30,31], rockfall [32], and hydraulic characteristics [33,34,35] can be well-measured using fiber Bragg grating (FBG) sensors and Brillouin-based distributed sensors. Because of the complicated mechanisms and diverse triggering factors, information on multiple parameters is crucial in a practical application to evaluate the safety of a slope accurately [6,36].…”

Section: Introductionmentioning

confidence: 99%

A Highly Integrated BOTDA/XFG Sensor on a Single Fiber for Simultaneous Multi-Parameter Monitoring of Slopes

et al. 2019

Sensors

A highly integrated sensing technology, combining a stimulated Brillouin scattering-based distributed sensor with XFG (fiber Bragg grating (FBG) and long-period fiber grating (LPFG)) sensors on a single fiber, is proposed for the simultaneous measurement of fully distributed and multiple discrete dynamic strains/temperatures. A multiparameter monitoring scheme for slope safety is developed using this integrated sensing technology. An indoor simulation test is carried out to verify its ability to simultaneously monitor a slope’s surface displacement, an anchor reinforcement’s axial force, and rockfall vibration. The experimental results show that distributed static strain and discrete dynamic strain can be well-measured simultaneously with little interference. The results also demonstrate the XFG sensors’ capability for multi-type and multipoint multiplexing. In addition, the proposed hybrid sensor system has potential for the monitoring of multiple slope parameters simultaneously.