Research On The Key Technologies Of Distributed Stress Sensing System For Landslide Based On OFDR

The mountainous area of our country is widely distributed.Due to geological structure,earthquake,heavy rain and human factors,landslides hazard are prone to occur.At present,there is no distributed stress monitoring equipment for landslides,water resources and hydropower engineering,dam engineering and other geotechnical engineering which can achieve long distance measurement,high spatial resolution,high sensitivity and fast response time.Based on the optical frequency domain reflectometry technology in distributed optical fiber sensor and instability criterion of landslide,this paper aims at the extending of OFDR measurement distance and the transverse stress and axial stress measurement and ultimately proposes a distributed sensing system scheme for the stress monitoring of landslides.Simultaneously,a distributed stress sensing system based on OFDR is established in laboratory,the transverse and axial stresses in the optical fiber are measured in different ways.The main contents of this paper are as follows:1.Starting from the analysis of landslide stability,the internal stress of landslides is studied.Through the analysis of the model,the safety factor of landslides is related to their internal stress,so the optical frequency domain reflectometry stress sensing technology can be used to monitor the landslide.Based on the fundamental theory of optical frequency domain reflectometry,the beat frequency signal model of OFDR is established and the measurement range and spatial resolution of the system are analyzed.The method of stress measurement based on the theory of bending loss in fiber and Rayleigh scattering theory is studied.2.The compensation for the nonlinear effect of the light source in the system is studied.Firstly,the generation and influence of the nonlinear effect of the light source are analyzed.For the compensation of nonlinear effect of light source,we introduce two algorithms of resampling and deskew filtering in this paper.The two algorithms are simulated and analyzed under the conditions of different measure distances and different nonlinear effects.The results show that the resampling method can obtain high spatial resolution in the short distance,but it is not suitable for long distance measurement.The compensation method based on the deskew filter has more advantages in long distance measurement.3.A distributed stress sensing experimental system based on OFDR is established,which can achieve long-distance fiber link measurement.A 13.3cm spatial resolution is obtained at 1808.1m.Meanwhile,the transverse stress and axial stress are measured.Transverse stresses of different sizes ranging from 5kg to 77.5kg(0.046Mpa-0.706Mpa)were measured.And the Rayleigh scattering intensity difference increases with the increase of stress.For axial stress,measurement range from 4.2g to 59.65g(0.838Mpa-11.906Mpa).For the stress difference of 1g,the wavelength shift is about 12.901 pm.At last,the realization scheme of the system in landslide is discussed.