Integrity Testing of Pile Cover Using Distributed Fibre Optic Sensing

Rui, Yun; Kechavarzi, Cédric; O'Leary, Frank; Barker, Chris; Nicholson, Duncan; Soga, Kenichi

doi:10.3390/s17122949

Cited by 41 publications

(23 citation statements)

References 33 publications

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“…DOFSs use optical fibers both as the sensing element and as the means of carrying the optical signals used for this purpose. [41] DFOS is gaining prominence in the field of structural health monitoring because of several advantages such as high spatial density of data, ease of installation, and reliability [42].…”

Section: Distributed Fiber Optical Sensor (Dfos) Technologymentioning

confidence: 99%

The Field Monitoring Experiment of the Roof Strata Movement in Coal Mining Based on DFOS

Hou

2020

Sensors

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Mining deformation of roof strata is the main cause of methane explosion, water inrush, and roof collapse accidents amid underground coal mining. To ensure the safety of coal mining, the distributed optical fiber sensor (DFOS) technology has been applied in the 150,313 working face by Yinying Coal Mine in Shanxi Province, north China to monitor the roof strata movement, so as to grasp the movement law of roof strata and make it serve for production. The optical fibers are laid out in the holes drilled through the overlying strata on the roadway roof and BOTDR technique is utilized to carry out the on-site monitoring. Prior to the on-site test, the coupling test of the fiber strain in the concrete anchorage, the calibration test of the fiber strain coefficient of the 5-mm steel strand (SS) fiber, and the test of the strain transfer performance of the SS fiber were carried out in the laboratory. The approaches for fiber laying-out in the holes and fiber's spatial positioning underground the coal mine have been optimized in the field. The indoor test results show that the high-strength SS optical fiber has a high strain transfer performance, which can be coupled with the concrete anchor with uniform deformation. This demonstrated the feasibility of SS fiber for monitoring strata movement theoretically and experimentally; and the law of roof strata fracturing and collapse is obtained from the field test results. This paper is a trial to study the whole process of dynamic movement of the deformation of roof strata. Eventually the study results will help Yinying Coal Mine to optimize mining design, prevent coal mine accidents, and provide detailed test basis for DFOS monitoring technique of roof strata movement.both ends along the long axis direction; when the two cracks increase to a certain length, cracks appear in the middle of the short axis and propagate to both ends; second, the cracks continue to expand in the long axis and the short axis directions, and are penetrated by the arc curve at four corners to form an "O-shaped" closed crack curve; finally, the "X-shaped" cracks are full of the "O-shaped" closed curve. At this time, the four sides of the fixed support plate will break into four geometrically movable rock blocks, the four rock blocks will rotate sink to the goaf like a cantilever beam. With the collapse of the broken roof strata, the broken rock blocks accumulate to be a loose rock body, the loose body then support the sinking roof strata, finally the Voussoir Beam Structure forms, which the Key Block is simplified into an arch with three articulations [1][2][3]. At present, Voussoir Beam hypothesis is widely used in China to design and guide coal mining. According to the hypothesis, the overlying strata movement of stope is divided into three zones in horizontal and vertical direction, as shown in Figure 1. The overburden of stope is divided into caving zone, fracture zone, and bending subsidence zone from bottom to top. In the advancing direction of the working face, Block A represents the Key Block ...

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Section: Distributed Fiber Optical Sensor (Dfos) Technologymentioning

confidence: 99%

The Field Monitoring Experiment of the Roof Strata Movement in Coal Mining Based on DFOS

Hou

2020

Sensors

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“…Nevertheless, important advances and interesting applications have been conducted recently with the use of Brillouin-based scattering DOFS. From research on crack monitoring in concrete pavements [ 18 ], surface microcracks detection and monitoring [ 19 ], shrinkage induced delamination detection for ultra-high performance concrete (UHPC) [ 20 ] and geotechnical engineering applications in the monitoring of the changes of the concrete curing temperature profile of piles [ 21 ] and soil slope during infiltration monitoring [ 22 ].…”

Section: Introductionmentioning

confidence: 99%

Embedded Distributed Optical Fiber Sensors in Reinforced Concrete Structures—A Case Study

Barrias

Casas

Villalba

2018

Sensors

100

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When using distributed optical fiber sensors (DOFS) on reinforced concrete structures, a compromise must be achieved between the protection requirements and robustness of the sensor deployment and the accuracy of the measurements both in the uncracked and cracked stages and under loading, unloading and reloading processes. With this in mind the authors have carried out an experiment where polyimide-coated DOFS were installed on two concrete beams, both embedded in the rebar elements and also bonded to the concrete surface. The specimens were subjected to a three-point load test where after cracking, they are unloaded and reloaded again to assess the capability of the sensor when applied to a real loading scenarios in concrete structures. Rayleigh Optical Frequency Domain Reflectometry (OFDR) was used as the most suitable technique for crack detection in reinforced concrete elements. To verify the reliability and accuracy of the DOFS measurements, additional strain gauges were also installed at three locations along the rebar. The results show the feasibility of using a thin coated polyimide DOFS directly bonded on the reinforcing bar without the need of indention or mechanization. A proposal for a Spectral Shift Quality (SSQ) threshold is also obtained and proposed for future works when using polyimide-coated DOFS bonded to rebars with cyanoacrylate adhesive.

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“…These temperature profiles discussed above are determined by a combination of factors, including the hydration heat produced by the concrete and the heat transfer rate between the pile and the surrounding soil. 10 If the measured temperature profile versus depth is consistent and each individual cable is also consistent, the pile is considered to be uniform in shape along the pile length, as shown in Figure 3. If not, it is assumed that some kind of defect existed in the pile as conceptually shown in Figure 6.…”

Section: Data Interpretationmentioning

confidence: 99%

Thermal integrity testing of cast in situ piles: An alternative interpretation approach

Sun

Elshafie

Barker

et al. 2020

Structural Health Monitoring

Self Cite

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Integrity testing of deep cast in situ concrete foundations is challenging due to the intrinsic nature of how these foundations are formed. Several integrity test methods have been developed and are well established, but each of these have strengths and weaknesses. A relatively recent integrity testing method is thermal integrity testing. The fundamental feature is the early age concrete release of heat during curing; anomalies such as voids, necking, bulging and/or soil intrusion inside the concrete body result in local temperature variations. Temperature sensors installed on the reinforcement cage collect detailed temperature data along the entire pile during concrete curing to allow empirical identification of these temperature variations. This article investigates a new approach to the interpretation of the temperature variations from thermal integrity testing of cast in situ concrete piles and presents a field case study of this approach. The approach uses the heat of hydration and heat transfer theory and employs numerical modelling using the finite element method. The finite element model can be customised for different concrete mixes and pile geometries. The predicted temperature profile from the numerical model is then compared, in a systematic manner, to the field test temperature data. Any temperature discrepancies indicate potential anomalies of the pile structure. The proposed new interpretation approach could potentially reduce construction costs and increase the anomaly detection accuracy compared to traditional interpretation methods.

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Integrity Testing of Pile Cover Using Distributed Fibre Optic Sensing

Cited by 41 publications

References 33 publications

The Field Monitoring Experiment of the Roof Strata Movement in Coal Mining Based on DFOS

The Field Monitoring Experiment of the Roof Strata Movement in Coal Mining Based on DFOS

Embedded Distributed Optical Fiber Sensors in Reinforced Concrete Structures—A Case Study

Thermal integrity testing of cast in situ piles: An alternative interpretation approach

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