Application Research Of Similar Material Moisture Content Monitoring Method Based On Distributed Heating Optical Fiber

Physical model test of similar materials is regarded as one of the important means to solve problems related to rock mechanics and mining engineering.Water content is the basic physical quantity of similar models.Water inside the model play a decisive role in similarity and accuracy of model tests.On the one hand,Roman Optical Time Domain Reflectometry(ROTDR)based on Raman scattering principle is introducedr.Meanwhile,combined with Active Heating Carbon Optical Fiber(AH-COF)water content monitoring method,distribution state of water field in each period of model curing process is monitored.On the other hand,mathematical model between the moisture content of similar materials and their mechanical properties was built through specimen tests,which played a key role in optimizing process and improving simulation accuracy of model tests.The basic principle of active heating carbon fiber water content monitoring method is described and the concept of stable temperature appreciation is put forward.Relationship between fiber and the thermal conductivity of similar materials during the heating process is described from the microscopic point of view by combining with the heat transfer principle.Relationship between the thermal conductivity and water content of similar materials is obtained.AH-COF water content monitoring system is designed.Equipment of AH-COF system is divided into three parts according to different functions:heating module,sensing module and data processing module.Working principle of each part is explained and factors that may affect the monitoring results of AH-COF moisture content monitoring system are analyzed comprehensively according to the similar materials.AH-COF sensor has a great impact on the measurement results of AH-COF moisture content monitoring system.Material and sealing properties of AH-COF sensor have been improved and new sensor can help to improve the measurement accuracy of moisture content.In order to make simulation effect of similar material model closer to the theoretical calculation value,an orthogonal experiment with 4 factors and 5 levels was designed to determine the ratio of similar materials.Different water content and ratio on mechanical properties of similar materials was analyzed.Linear regression of the mechanical properties of similar materials was obtained.Reliability analysis of regression equations was carried out with the help of actual geological data.Calculated error range was 5.2%?13.7%,which could meet the basic requirements of model test.By substituting the rock mechanics property parameters into the regression equations,the ratio suitable for the model test of similar materials and the water content value of the model are obtained.In order to establish the functional relationship between steady temperature appreciation and water content of similar materials,a calibration test was designed.The test results showed that the changes of the steady temperature appreciation of different kinds of similar materials under different water content were characterized by a law of rapid growth in the early stage of heating and eventually stabilization.Thermal conductivity of similar materials was obtained through fitting results of steady temperature appreciation and time logarithm.Linear fitting of thermal conductivity and water content of different kinds of similar materials was carried out respectively to obtain the relationship between them.Real-time monitoring of water content was realized.FDR was introduced to monitor the moisture content of similar materials.By comparing and verifying the monitoring data of FDR and AH-COF water content monitoring system,it can be known that the maximum measurement error is 4.2%when the moisture content is greater than 3%,which proves that AH-COF water content monitoring method has high measurement reliability.At the same time,kriging interpolation method was introduced to interpolate water content data of the model.By comparing and analyzing the interpolation data with actual monitoring data,the relative error range between the two was found to be 0.43%?2.91%,meeting the test requirements.With the increase of curing time,the internal moisture content of model presents an increasing trapezoidal distribution trend from top to bottom.When model was maintained to the 30th day,model moisture content range was 3-6%,which was most close to theoretical calculation of the optimal moisture content range of 4?5.7%.In addition,the error between each physical and mechanical numerical distribution range of the model and the theoretical calculation value is not more than 20%,which proves that the plane model of similar materials reaches the optimal test state by the 30th day of curing.