AHFO Monitoring Method And Its Application In Moisture Migration Of Soil

The moisture field is an important factor affecting the engineering properties of rock and soil,and its distribution characteristics and change laws are important topics for long-term research in geotechnical engineering.It is very important for the in-situ monitoring of the soil moisture field since the soil moisture field changes with the environment.The in-situ monitoring of the soil moisture field has always been a difficult problem for the engineering geological community duing to the lack of corresponding monitoring technology.In recent years,with the continuous development of optical fiber sensing technology,distributed optical fiber sensing technology has been applied continuously in geological engineering and has achieved very good results.This paper uses an AHFO in-situ monitoring system based on internally-heated carbon fiber-optic cable in the soil moisture field by Raman scattered light time-domain reflectometry(ROTDR).The system is compared systematically through theoretical analysis,laboratory tests and field tests.Demonstrated the feasibility and accuracy of this system to monitor the soil moisture field,and achieved the following results:1.The distributed in-situ monitoring system(AHFO)of soil moisture field based on internally heated carbon fiber cable was perfected.The measurement principle and module composition of AHFO were introduced in detail,and the operating instructions of the system were completed.2.An indoor model test was designed.Three different directions of seepage methods and moisture migration of two soils were tested using the AHFO method.The unsaturated seepage of sand and clay was measured.The spatial resolution of the water content data was reaching 2 cm,and the phenomenon of "priority flow" that could not be observed by the conventional moisture content measurement method was observed.3.The AHFO in-situ test scheme for the outdoor soil moisture field was designed.The change law of the moisture field in the soil under multiple simulated rainfall conditions was analyzed based on the measured results,and the soil was observed from unsaturated to saturated.The whole process of change of moisture content confirms the good effect of the AHFO in-situ test.4.The law of vertical water movement under the action of constant head was studied based on the AHFO method.According to the water-soil characteristic curve,using the empirical relationship between the permeability coefficient of the unsaturated soil and the soil characteristic curve of Van Genuchten,combined with the measured value of the soil water content AHFO method,the relevant physical characteristics parameters of the soil were obtained by the fitting method,making the infiltration The determination of the coefficient is more convenient and accurate;a modified Green-Ampt model is proposed based on this.The test results show that the revised model is closer to the measured value and the prediction accuracy is improved by nearly 10 times.5.The AHFO method uses the relationship between the temperature characteristic value and the moisture content during heating of the carbon fiber heating cable to measure the moisture content in the soil.It has distributed,long distance,good durability,non-destructive in-situ testing,etc.The advantages can be applied to the monitoring of the moisture field in the fields of geology and geotechnical engineering,agriculture,water conservancy,etc.The application prospect is very broad.