Research & Development And Experimental Study On Monitoring Technology Of Soil Seepage Field Based On FBG

The seepage field in rock and soil is an important factor affecting the stability of dams,embankments,channels and foundation pits.In views of the shortcomings and limitations of conventional seepage monitoring methods,based on the technology of fiber Bragg grating(FBG)and the principle of thermal convection,an internally heated corundum tube FBG seepage sensor(referred to as IHAT-FBG-S)is developed by this paper;Based on the indoor experiments,the concept of eigenvalue temperature is cited,the relationship between the eigenvalue temperature measured by IHAT-FBG-S and the water flow velocity at different flow rates and heating powers is studied,the feasibility of the FBG for seepage monitoring is verified.This research work and results of the paper are summarized as follows:(1)The existing monitoring technology and its shortcomings of soil seepage field are summarized,the advantages of optical fiber temperature measurement technology and its applicability in rock and soil body seepage field monitoring are introduced.(2)Based on the principle of FBG temperature measurement and the heat transfer law of linear heat source,the theoretical equation of seepage rate monitoring is derived,and the feasibility of FBG for monitoring the seepage rate and flow direction identification in soil are demonstrated.(3)An IHAT-FBG-S sensor that can actively heat the surrounding soil and the metal capillary temperature sensor are developed,the manufacturing process of the sensor is introduced,the change law of temperature rise with time is obtained,and the quasi-distributed monitoring of seepage in soil is realized.(4)The difference of the measurement range of the seepage rate in different environments of the soil is analyzed.The seepage rate is negatively correlated with the eigenvalue temperature.It is a quadratic function relationship in pure water media and a piecewise linear function relationship in sand soil.(5)By analyzing the change law of the seepage eigenvalue temperature of the front and back water surface of the IHAT-FBG-S sensor,the direction of seepage flow velocity in the soil is realized.(6)The influence of heating time and heating power of IHAT-FBG-S sensor on seepage monitoring results is analyzed.The time required for the IHAT-FBG-S sensor to reach temperature stabilization in pure water media is shorter than that in sand media,and the heating stability time in sand media is greatly affected by the flow rate.The eigenvalue temperature is linearly related to the heating power,and the temperature difference between different IHAT-FBG-S sensors increases with the increase of heating power.Increasing the heating power within a certain range can improve the accuracy and sensitivity of seepage monitoring in soil.(7)The variation range of the temperature field in the sand and soil before and after the seepage is analyzed,and the influence law of the seepage velocity on the temperature field is obtained.