Water Leakage Detection Using Optical Fiber at the Peribonka Dam

2018

Purpose The spatial resolution of seepage monitoring methods based on fiber Bragg grating (FBG) temperature sensing technology is limited by the distance between measurement points. Improving the spatial resolution for a given number of measurement points is a prerequisite for popularizing this technology in the seepage monitoring of rockfill dams. The purpose of this paper is to address this problem. Design/methodology/approach This paper proposes a mobile-distributed seepage monitoring method based on the FBG-hydrothermal cycling seepage monitoring system. In this method, the positions of the measurement points are changed by freely dragging the FBG sensing cluster within the inner tube of a dual-tube structure, consisting of an inner polytetrafluoroethylene tube and outer polyethylene of raised temperature resistance heating tube. Findings A seepage velocity calibration test was carried out using the improved monitoring system. The results showed that under a constant seepage velocity, the use of the dual-tube structure enables faster cooling, and the cooling rate accelerates with an increase in the diameter of the inner tube. The use of the dual-tube structure can improve the sensitivity of the seepage evaluation index ζv to the seepage velocity. When the inner diameter increases, ζv becomes more sensitive to the seepage velocity. Originality/value A mobile-distributed seepage monitoring method based on FBG sensing technology is proposed in which the FBG sensors are not fixed. Instead, the positions of the measurement points are changed to improve the spatial resolution. Meanwhile, the use of the dual-tube structure in the presented monitoring system can improve its sensitivity.

Section: Introductionmentioning

confidence: 99%

Mobile-distributed seepage monitoring method based on fiber Bragg grating sensing technology

Jiang

Zheng

2018

“…Optical fiber sensing technology was identified as an effective approach to monitor seepage and overcome difficulties in rockfill dam leak monitoring. Presently, optical fiber sensing technology has been successfully used to monitor seepage [9][10][11][12][13][14][15][16]. These methods are mainly based on the coupling between the seepage field and temperature field [17,18], To be specific: (1) the seepage allows the osmotic flow to contribute in the heat transfer and exchange within the porous medium, which impacts the temperature distribution of the porous medium, (2) the change in the temperature field of the porous medium leads to changes in the seepage coefficient.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of leak detection using mobile distributed monitoring system

Chen

Zheng

et al. 2017

Smart Mater. Struct.

The leak detection of rockfill dams is currently hindered by spatial and temporal randomness and wide monitoring range. The spatial resolution of fiber Bragg grating (FBG) temperature sensing technology is related to the distance between measuring points. As a result, the number of measuring points should be increased to ensure that the precise location of the leak is detected. However, this leads to a higher monitoring cost. Consequently, it is difficult to promote and apply this technology to effectively monitor rockfill dam leakage. In this paper, a practical mobile distributed monitoring system with dual-tubes is used by combining the FBG sensing system and hydrothermal cycling system. This dual-tube structure is composed of an outer polyethylene of raised temperature resistance heating pipe, an inner polytetrafluoroethylene tube, and a FBG sensor string, among which, the FBG sensor string can be dragged freely in the internal tube to change the position of the measuring points and improve the spatial resolution. In order to test the effectiveness of the system, the large-scale model test of concentrated leakage in 13 working conditions is carried out by identifying the location, quantity, and leakage rate of leakage passage. Based on Newton's law of cooling, the leakage state is identified using the seepage identification index ζ v that was confirmed according to the cooling curve. Results suggested that the monitoring system shows high sensitivity and can improve the spatial resolution with limited measuring points, and thus better locate the leakage area. In addition, the seepage identification index ζ v correlated well with the leakage rate qualitatively.

“…Fiber optic pyrometry and the temperature tracer method have combined into an effective way to realize extensively distributed and automatic monitoring of rockfill dams. In this aspect, many researchers have carried out theoretical analyses, 14,15 numerical simulations, 5,16 model tests, 17–19 and applying the technology to practical engineering 20,21 for its validity. The seepage monitoring method based on the distributed fiber optic temperature sensing technology is making use of the temperature anomalies before and after a seepage occurrence to identify the seepage state.…”

Section: Introductionmentioning

confidence: 99%

“…In order to improve the measurement accuracy, the sensing optical cable is usually heated with resistance wires when used to identify the seepage state according to the temperature increment at the monitoring point. 17,19–22…”

Section: Introductionmentioning

confidence: 99%

An experimental study: Fiber Bragg grating–hydrothermal cycling integration system for seepage monitoring of rockfill dams

Chen

Cheng

Structural Health Monitoring

et al. 2016

In order to make up defects liable for the conventional monitoring of rockfill dam seepage in spatial inconsequence and low efficiency, a new monitoring system is proposed based on the heating technique incorporated in the temperature tracer method, that is, the integrated system of fiber Bragg grating temperature sensing and hydrothermal cycling. The system has a boiler as its heating device, and heated water from boiler is admitted through redistributor and circular warm pipelines, in which fiber Bragg grating sensors are embedded in advance for measuring the water temperature, thereby the seepage behavior is identified from the correlative fields of temperature and seepage. A coefficient ζv, according to Newton’s law of cooling, is then fitted out by pipeline cooling curves and used as a new way to identify the seepage state. The temperature–time–travel curves for the cooling period have proved by calibration tests to be, in general, consistent with the mathematical model of temperature variations under Newton’s law of cooling, thereby to inverting the seepage velocity through the fitting formula of it with ζv. With the test model of concentrative leakage established in regard to the location, amount of leakage passages, and leakage rate, multi-condition tests have been conducted which conclude that the proposed method is capable of positioning leakage and quantifying seepage velocity; therefore, it is valid for seepage monitoring and identification.