Review on monitoring of pavement subgrade settlement: Influencing factor, measurement and advancement

Monitoring road subgrade settlement is crucial for maintaining pavement integrity, durability, and safety. It is important to understand the causes and mechanism of the settlement ahead of implementing monitoring methods, while few studies have examined the influencing factors comprehensively. On the other hand, there are many existing and emerging monitoring methods, such as In-SAR, GPR etc., each possessing different adaptability and accuracy level. There is a gap of knowledge about commons and differences among these methods in terms of working principle, data processing, precision level, as well as practicability. The objective of this paper is to provide reference of the state-of-the-art and state-of-the-practice of subgrade settlement monitoring methods for the engineers and researchers. A comprehensive literature review was conducted in the aspects of influencing factor, measurement method and advancements in monitoring subgrade settlement. A framework of joint monitoring system is proposed subsequently and suggestions for future studies are presented.