Distributed optical fiber sensing technology and system for earth-rock dam seepage line monitoring

Abstract

The invention discloses a high-precision distributed optical fiber sensing and monitoring technical scheme and system. Its optical demodulator adopts high-precision pre-pulse Brillouin optical time domain analyzer PPP-BOTDA or Brillouin-Rayleigh synthesis system; its sensing optical cable adopts photoelectric composite cable with sufficient electric heating energy to ensure electric heating temperature rise The mutation signal whose amplitude is at the intersection of the optical fiber and the soaking line can be reliably identified; the signal-to-noise ratio of the system is as high as 10-20, which enables efficient and reliable observation of the soaking line and the groundwater level of the dam base. It can be used for large-scale-time-space double-coverage online telemetry of the groundwater level of the soil-rock dam soaking line and the anti-seepage curtain of the dam foundation. Its "one machine with multiple functions" has obvious advantages, and it can also measure the concentrated leakage of dams, silt in reservoirs, etc. Specific implementation methods are provided, including the layout method of the sensing optical cable for the monitoring of the soaking line and groundwater level - the wave pattern and technical details of the laying of the optical cable, which can effectively guarantee the survival rate of the optical fiber and minimize the interference to the dam construction.

Description

technical field [0001] The invention relates to a distributed optical fiber sensing technology type and system for earth-rock dam seepage line monitoring, which can realize efficient and reliable real-time online remote measurement of local material dams—especially high earth-rock dam seepage lines and their dam foundation anti-seepage curtain groundwater levels. Background technique [0002] The seepage line monitoring of earth-rock dams is an important project of dam safety monitoring. Based on this, the seepage state and its temporal and spatial evolution trends during the dam operation period are known, which is useful for evaluating the working status and safety state of earth-rock dams and predicting whether they will face seepage. The potential risk of leakage accidents is of great significance. Conventional equipment such as piezometric tubes and piezometers currently in use are single-point monitoring, which has the advantages of less information collection, dif...

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Problems solved by technology

[0006] (2) Interference with dam construction: multiple monitoring sections need to be arranged within the length of the dam, and each section has multiple optical fibers intersecting the filling surface. The laying operation of optical fibers will interfere with the construction, which is especially obvious in core-wall high earth-rock dams

[0007] (3) The signal-to-noise ratio of the system is low: Raman scattering light intensity is extremely weak (1000 times smaller than Rayleigh scattering ［1］ ), which limits its spatial resolution to meter-level (0.5-1m)

This is particularly unfavorable for observations at abrupt temperature changes such as the fiber-soaked line intersection, where temperature effects are averaged out and errors increase within the resolution range

The Raman demodulator has a large range but the accuracy (±1oC) is not ideal. For an area with a high temperature gradient such as the soaking line, the averaging effect within the spatial resolution range increases the source of error.

Combined with the above-mentioned optical fiber temperature rise is only on the order of 2~8oC, resulting in the low signal-to-noise ratio (SNR) of the whole system, so that the effective signal is often interfered by strong noise

Therefore, the Raman-type DTS sensing system is difficult to apply to the narrow local temperature mutation of high dams - occasions with high precision requirements

[0008] It can be seen that the general products of Raman optical fiber temperature measurement have a low SNR for the high requirements of capturing early signs of high dam leakage, and their practicability is not ideal.

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