| Moisture content is the most important quantitative index to measure the water field in soil.The change of soil moisture content determines the physical and mechanical properties of soil when the soil composition and structure are constant.Therefore,accurate and real-time monitoring of soil moisture content change is the key to understand the change of soil engineering properties.In addition,soil moisture content is closely related to agricultural production;the development of soil moisture content is very important for the fine management of agricultural water use,the transformation of extensive irrigation mode,and the realization of agricultural modernization.The Fiber Bragg Grating(FBG)sensing technology,with advantages such as high precision,high sensitive,anti-interference,small size,easy realization of connected nets,and long-term stability,is widely used in structural and geotechnical engineering monitoring.Based on the FBG sensing technology for soil moisture content monitoring developed by the author’s group,this work aims to improve the performance of the monitoring system.First,a data post-processing system is designed and developed to improve the whole performance and practicability of the system.Then,the measurement errors of the system are analyzed through laboratory simulation tests.The main conclusions are summarized as below:(1)The importance of developing soil moisture content monitoring technology is clarified in detail.Research progress of various soil moisture content monitoring technology at home and abroad,and their advantages and disadvantages are analyzed and concluded as well.Besides,based on it,the advantages and application status of the FBG sensing technology are introduced.(2)FBG-based soil moisture content monitoring technology and soil moisture content caculation method based on soil thermal properties are illustrated.The linear function model and the piecewise function model for soil moisture content caculation are derived.The functional modules of NZS-FBG-A01,FBG-based moisture content monitoring system,are analyzed in detail.(3)The existing problems of NZS-FBG-A01 monitoring system are analyzed,and a relatively standard operation steps of A01 system software for moisture content calibration test is proposed.Based on Matlab GUI(Graphical User Interface),A moisture data post-processing tool is designed and developed to provide complementary functions.The BE(boundary effect)parameter is defined to realize the quantitative evaluation of the influence of boundary effect on the data measured by monitoring system.A user-friendly graphical interface is designed to realize the automatic caculation for the moisture calculation model.Cubic interpolation algorithm and bi-cubic interpolation algorithm are used to realize the automatic generation of temperature nephogram and moisture content nephogram.Finally,the use of the system is illustrated by an example.(4)The influence of seasonal environment temperature changes on the measurement results of FBG-based soil moisture content monitoring system is analyzed.A series of parallel experiments are designed to quantitatively analyze the influence of environmental temperature on temperature characteristic values through significance analysis.Finally,the correction coefficient of environment temperature for monitoring system is given,which can help to solve the problem of selecting environmental temperature correction parameters for FBG-based soil moisture content monitoring system.(5)The stability of repeated measurement results of FBG-based soil moisture content monitoring system under the same soil dry density is investigated by statistical method.A horizontal translation correction method for soil moisture content calculation model is introduced to correct the errors caused by the change of soil dry density.The measurement error caused by the change of soil dry density was corrected,and the soil moisture content calculation model was improved. |
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