Development And Application Of Quasi-distributed Monitoring Technology For Soil Moisture Field Based On FBG

The effective monitoring of the moisture field is of great significance for the prevention of geological disasters,safety construction of geotechnical engineering,and agricultural production.However,the conventional moisture monitoring technology cannot meet the monitoring needs of modern production and living.Based on theoretical analysis and experimental research,this paper develops a quasi-distributed monitoring system for soil moisture field based on FBG(F-QDMS),and introduces heating method,packaging method,rate determination test and system integration.The measurement indicators of the system were determined,and the factors influencing the measurement results were analyzed.Two application examples demonstrate its feasibility.Two application examples test results show that F-QDMS is feasible for quasi-distributed in-situ monitoring for moisture field,and its test performance is obviously higher than the conventional moisture in-situ test method.The relevant results and conclusions of the paper are as follows:1.With the introduction of FBG fiber technology,a distributed measurement method for moisture field was proposed.The principle of this method is that according to the differences in the thermal conductivity of water and soil,the relationship among the temperature characteristic value ?At,the water content w in the soil and the seepage rate v is established.(w=k1?Tt+b1,v=a?Tt + b)2.Based on the FBG technology,a quasi-distributed monitoring system for soil moisture field(F-QDMS)was developed.The system consists of three parts:IHAT-FBG sensor,heating system,and FBG monitoring data processing system.It can realize quasi-distribution and large-scale in-situ monitoring of soil moisture field.3.The IHAT-FBG sensor was developed.Corundum was used as the encapsulation material,and internal heating and single-end fixing techniques were adopted.The packaging method and manufacturing process were introduced.The effect of quasi-distributed monitoring was achieved through a series arrangement.4.The F-QDMS moisture field determination method was given.The water content and seepage rate determination tests were conducted to determine the measurement coefficients of F-QDMS.(k1?b1?a?b.)5.The factors that affect the F-QDMS measurement results were explored.The results showed that the degree of soil compaction was the main influencing factor.Under the condition of the same rate,the measurement results increased with the increase of soil compactness.The ambient temperature and other factors had no influence on the measurement results;factors such as sensor size and heating power can be calibrated and eliminated through standardization of the system.The F-QDMS measurements were compared with the traditional drying method and the F-QDMS measurement error was 3%.6.The F-QDMS was carried out to monitor the change of the internal water content of the soil under the condition of drainage and irrigation.The results showed that the system could effectively measure the internal moisture field of the soil,and the measurement results were consistent with the results of the drying method.When the soil structure was measured,there is no disturbance,which could realize the quasi-distribution of the moisture field in the soil and long-term in-situ non-disturbance monitoring.7.A geotechnical centrifuge test was conducted to monitor changes in the internal moisture content of loess by F-QDMS.The results showed that the monitoring effect of this system was stable and free from electromagnetic interference,and real-time monitoring of moisture content in the geotechnical centrifuge could be realized.8.The research results of this paper showed that F-QDMS had the advantages of simple method,stable measurement effect,quasi-distributed monitoring,long-term and wide-range in-situ monitoring,and can be promoted in soil moisture monitoring field.The research results of the thesis indicated that F-QDMS had the advantages of simple test,quasi-distributed monitoring,stable measurement effect,and undisturbed in-situ monitoring.Its application prospect is very broad.