EXPERIMENTAL STUDY ON RAPID DETERMINATION OF SOIL MOISTURE CONTENT BASED ON FIBER BRAGG GRATING TECHNIQUE

Soil moisture content has a great influence on the strength, deformation and permeability of soils. How to measure soil moisture content rapidly is an important subject in foundation engineering. Aiming at the problems such as poor real-time ability in existing measurements, a new method based on fiber Bragg grating(FBG)technique for rapid determination of soil moisture content is proposed in this paper. By using free-fall balls, impact loads are applied to FBG strain sensors embedded in sandy soil. The strains and their variation of sensors in this process are measured. Based on the analysis of the variation of strain, the concept of peak strain is introduced. By controlling variable method, an indoor test on sandy soil is carried out under the condition of different moisture contents. The experimental results show that peak strain decreases with increasing of moisture content. There is a nearly linear relationship between the moisture content and the peak strain. Therefore, soil moisture content can be estimated by an empirical calculation formula. The possible errors in the method are analyzed, and the methods for reducing errors are given.