Optical-Fiber-Embedded Beam for Subgrade Distributed Settlement Monitoring: Experiments and Numerical Modeling

Abstract

In this study, Brillouin optical time domain analysis (BOTDA) sensing technology was utilized for monitoring settlement in a similarity model of a highway subgrade. As contact winding cannot be used for an optical fiber that is buried directly in the soil, uncoupling between the fiber and the soil can occur. Thus, an optical-fiber-embedded beam (OFEB) was developed, and a method for measuring and calculating the beam’s deformation was proposed. A calibration test and a test on a similarity model of a subgrade were carried out to investigate the applicability and monitoring accuracy of the OFEB. It was concluded that the OFEB can accurately measure beam deflection, and the maximum relative error between measurements by the optical fiber and a displacement transducer was approximately 5%. The OFEB was embedded directly into a similarity model of a subgrade to monitor settlement. The deflection deformation of the OFEB was found to be close to the subgrade settlement over a certain settlement range, with a relative error below 8.1%. Thus, the OFEB can be used to measure large-range distributed settlement in a subgrade. A numerical simulation was performed to identify appropriate beam dimensions and material design parameters, thereby extending the measurement range before decoupling of the OFEB and the soil occurs. The enhancement of the measurement range and the accuracy of the OFEB based on the preliminary experiments carried out in this study enables further investigation of settlement monitoring.

Review of Sensor-Based Subgrade Distress Identifications

“…Ground-penetrating radar (GPR) [22][23][24][25][26] Total station [27][28][29][30][31] InSAR [32][33][34][35][36] Distributed optical fiber [37][38][39][40][41] Subgrade frost heaving Ground-penetrating radar (GPR) [42][43][44][45] Multi-sensor embedding [46][47][48][49][50] Weak subgrade Falling weight deflectometer (FWD) [51][52][53][54][55][56]…”

“…Weng Xiaolin et al [43] used distributed optical fibers to measure the strain characteristics in the top and bottom layers of cement concrete pavement, which were affected by different foundation settlement degrees. Li Zhen [44,45] and others developed a distributed optical fiber and proposed a method to measure and calculate the beam deformation. A calibration test and a subgrade similarity model test were carried out to study the applicability and monitoring accuracy of the distributed optical fiber.…”