BOTDA Method For Strain Monitoring In Similar Material Model

Similar material model experiment is an important means to study the law of rock movement and deformation,which is widely used in water conservancy,building materials and mining and other fields.The application of BOTDA technology in similar simulation experiment can acquire the strain information of each stratum in the model,monitor and record the space,time and intensity of stratum deformation in real time,and explore the deformation law of each stratum through further analysis.This paper focuses on the influencing factors of sensing signal of BOTDA sensor system,the strain sensing performance of BOTDA system and the application effect of BOTDA technology in similar material model experiment.The main research results are as follows:(1)The factors affecting the monitoring signal of BOTDA distributed optical fiber sensing system are revealed.Taking the pulse width,spatial sampling interval and average sampling times as the research objects,the influence of different parameter settings on temperature monitoring results is explored by using control variable method.According to the analysis of experimental results,it is concluded that under the condition of experimental optical fiber length(15m),pulse width is 5ns,and spatial sampling interval.When the interval is 0.04 m and the average sampling times are 30000,the temperature measurement results are closest to the setting temperature of the constant temperature water tank,and the difference of temperature measured under three different setting temperatures(30,40,50)is not more than 0.06 C..(2)The strain sensing performance of BOTDA distributed optical fiber sensing system is analyzed experimentally.According to the measured results,the tensile strain of single-mode bare fibers should be no more than 1863.72,and that of high-precision strain testing fibers should be no more than 2422.05.The strain transfer coefficients of single-mode bare fibers are between 99.5% and 100.9% before reaching the limit value,and those of high precision strain testing fibers are between 99.7% and 101.2%.(3)The BOTDA distributed optical fiber monitoring experiment of similar material model is carried out,and the basic law of strain change of vertical optical fiber under mining influence is obtained.The response relationship of vertical optical fiber to the position of working face can be divided into three parts.The first part is that the working face is close to the position of optical fiber,the measurement value of optical fiber near the coal seam is negative,and the optical fiber is under pressure.In the second part,through the location of the optical fiber,the optical fiber changes from the former pressure to tension,and the peak strain shifts upward with the advancing of the working face;in the third part,the optical fiber changes from tension to compression when the working face is far from the location of the optical fiber.