Study on actively heated fiber Bragg grating sensing technology for expansive soil moisture considering the influence of cracks

• Published in: Measurement : journal of the International Measurement Confederation 2023-08, Vol.218, p.113087, Article 113087
• Main Authors: Li, Jie, Zhu, Hong-Hu, Wu, Bing, Hu, Le-Le, Liu, Xi-Feng, Shi, Bin
• Format: Article
• Language: English
• Subjects: Crack; Expansive soil; Fiber Bragg grating (FBG); Geotechnical monitoring; Moisture content; Thermal conductivity
• ISSN: 0263-2241
• DOI: 10.1016/j.measurement.2023.113087

•The actively heated FBG technology measures the moisture content of expansive soil.•The influence of cracks on measuring soil moisture content is investigated.•A modified function is proposed to eliminate the measurement error.•The root mean square error after modification is reduced to 0.030 m3·m−3. Accurately moisture content measurement is crucial in addressing engineering problems of expansive soil with cracks. In this study, the actively heated fiber Bragg grating (AH-FBG) sensing technology was used to measure in-situ moisture contents of expansive soil. The impact of soil cracks on the measurements was investigated through a series of numerical simulations, and a modified function was proposed to eliminate measurement errors. The results show that the Cai model can accurately describe the relationship between the thermal conductivity and moisture content, and is thus utilized as the calibration model. Under the heating strategy, the influence range of the sensor is roughly 4 cm in the radial direction. Cracks within that range hinder heat transmission, leading to underestimation of moisture contents. The RMSE of the measurements after modification is reduced to 0.030 m3·m−3, which verifies that AH-FBG sensing technology can be extended to the reliable measurement of expansive soil moisture.