Experimental study on buried pipeline instrumented with fiber optic sensors under ground collapse

In recent years, the pipeline accidents caused by ground collapse are frequently reported. However, the relevant studies are still lagging behind, and there are few theories to predict the deformation and mechanical characteristics of buried pipelines and surrounding soils in the process of ground settlement and collapse. In this study, the stress state of the pipeline and soil settlements during ground collapse are investigated through fiber Bragg grating (FBG)-based model tests, and the method for calculating the bending moment of the pipeline using fiber-optic strain measurements is derived. The test results show that: (1) The compressive strains accumulate on the pipeline top and bottom with the increase of collapse volume, and both the pipeline sidewalls are in the strain state of tension. (2) According to the FBG strain monitoring results, the development of soil deformation can be divided into three stages, i.e., the stress redistribution stage, the creep compression stage and the stability stage after collapse. (3) The ground settlement pattern fits well with the modified Gaussian distribution. On this basis, the mathematical model between the horizontal strain measured by the fiber optic sensors and the ground settlement is established. At the same time, the results of theoretical calculation and experimental data are compared, and they appear to agree well with each other. This work provides a new approach to effectively evaluate the safety and implement hazard warning of buried pipelines.