Novel FBG-Based Effective Stress Cell for Direct Measurement of Effective Stress in Saturated Soil

In this study, a novel effective stress cell based on fiber Bragg grating (FBG) sensing technology is developed for direct measurement of effective stress in saturated soil. The primary concept of direct measurement is that the pore-water pressures acting on both front and back surfaces of the sensing plate do not induce the deflection of the sensing plate, and thus the measured deflection of the sensing plate is caused by the effective stress only. The calibration results of the FBG-based effective stress cell (FBG-ESC) demonstrate a good linearity between the Bragg wavelength of the FBG sensor and the applied pressure. The workability and performance of the FBG-ESC in a saturated soil have been verified in a physical model test subjected to vertical pressures. It is found that the effective stress data directly measured by the FBG-ESC agree well with the effective stress values calculated, according to the effective stress principle, from the difference between the total stress and pore-water pressure measured by conventional transducers. All these results indicate that the novel FBG-ESC is capable of directly measuring the effective stress in a saturated soil.