Safety evaluation of the hidden suspended pipeline based on strain criteria

When a pipeline runs through a goaf, the pipeline may be faced with the problem of hidden suspension. And if the hidden suspension is long, the pipeline will undergo big stress and strain, and even failure of serious rupture. Based on nonlinear finite element method, a 3D numerical model was built up to perform mechanical calculation on hidden suspended pipelines. Then, the safety of hidden suspended pipelines was evaluated according to the strain based criteria. In this model, multiple non-linear factors (e.g. pipe material, pipe-soil interaction and large geometric deformation) were taken into consideration with the non-linear soil spring element to simulate the pipe-soil interaction and the shell element to describe the pipeline deformation. And finally, the stress and strain responses of hidden suspended pipelines in different working conditions were analyzed, and the ultimate limit state of hidden suspended pipelines discriminated according to the stress criteria was compared with that obtained according to the strain failure criteria. It is shown that the stress based criteria is more conservative and the strain based criteria can make full use of the plastic property of pipe material. The research result can provide theoretical basis for the integrity management and safety evaluation of pipelines.