Study on calibration model of soil water content based on actively heated fiber-optic FBG method in the in-situ test

Abstract

• The calibration model for water content measurement is studied by AHFO-FBG method. • Two semi-empirical calibration models for calculating water content are deduced. • The modified calibration model considering dry density is proposed. • The feasibility of the modified calibration model is verified and analyzed. • AHFO-FBG method has unique advantages for laboratory tests accurately. In the water content measurement technology based on actively heated fiber-optic (AHFO) method, how to establish the calibration model between the temperature characteristic value and the water content is very important. Given shortcomings of the existing calibration models, the optimal calibration model was established. On this basis, a modified calibration model considering the change of dry density was proposed by using the actively heated fiber-optic fiber Bragg grating (AHFO-FBG) method, and the feasibility of the model was verified and analyzed. The results show that the Côté and Konrad model is the best model for water content calculation; in the in-situ water content measurement, if the dry density of the soil is small (≤1.5 g/cm 3 ), the modified Côté and Konrad calibration model should be used. The research results are of great significance to guide the application of the AHFO-FBG method in the in-situ soil water content monitoring.