Theoretical model updating on interfacial degradation and transfer mechanisms of multi-layer pavement structures based on FBG monitoring information in field

The interfacial properties of multi-layer composite structures govern their overall load-bearing capacity. Therefore, it is necessary to investigate the influence of interfacial degradation on the internal force transfer mechanism of multi-layer composite structures. This paper proposes an improved interfacial degradation analytical model that can be directly invoked within the transfer matrix method framework. By continuously adjusting the elastic modulus of a thin transfer layer, the model simulates the life cycle of an interface, from ideal bonding to complete slip state. This approach overcomes the limitations of conventional models with difficulty to calibrate interfacial parameters. The reliability of the theoretical model has been verified through finite element calibration of interfacial parameters. Furthermore, specially packaged multifunctional fiber Bragg grating (FBG) sensors for strain and temperature measurement of pavement has been developed, and a multi-scale optical fiber monitoring network covering both local and global areas has been established for in-site monitoring of multi-layer pavement structures. Using the continuous monitoring data in 5 years, a non-destructive method for assessing interfacial degradation based on plastic deformation propagation is proposed. The results reveal that the temperature sensitivity of the structural concrete surface layer initially increases, then decreases before gradually stabilizing, thereby clearly characterizing the entire process of interfacial degradation. In-site vehicle loading tests indicate that the actual interfacial contact conditions between structural layers are semi-continuous and semi-smooth, with these boundary conditions significantly reducing the decay rate of horizontal structural stresses. This study establishes a closed-loop research framework integrating “Theory-Numerical Simulation- Monitoring in Field”, providing innovative concepts and mature techniques for the long-term performance prediction and precise maintenance decision-making of multi-layer composite pavements. © 2026 Elsevier Ltd.