# Numerical Simulation Study on the Performance of Buried Pipelines under the Action of Faults
## 5 Conclusions  
Based on advanced finite element simulation tools, a model of an interacting soil-pipeline system is established, and the mechanical behavior of buried steel pipelines crossing an active strike-slip fault was investigated, considering buried steel pipelines crossing the fault plane at various angles. Furthermore, this paper examines the mechanical behavior of buried steel pipelines under different fault types, their internal pressure, and their wall thickness.  
1. Among the three common damage modes, beam buckling damage is less threatening to the buried pipeline. The results show that beam buckling damage will not occur in the buried pipeline at the 1.5 m burial depth taken in this study. Shell buckling damage occurs at a small fault displacement (0.82 m), and the axial compressive strain of the pipeline develops rapidly with the increase in the fault displacement, which leads to outward bulging of the pipeline and even rupture. Although tensile failure may also occur, its critical failure displacement of 2.72 m is more than three times that of shell buckling failure, and the occurrence of shell buckling failure will accelerate the development of the maximum axial tensile strain of the pipeline;
2. Compared to a single type of fault action, combined fault action has a more significant impact on buried pipelines, and the stress and strain of pipelines increase more rapidly when reverse faults exist. Under the action of strike-slip reverse faults, the threat is greater when the fault dip angle is 60 degrees;
3. The internal pressure of a pipeline can, to some extent, enhance its ability to resist deformation, but excessive internal pressure can accelerate the development of stress  
Figure 14: Deformation diagram of pipes under different kinds of wall thicknesses: (**a**) 15.33 mm; (**b**) 18.4 mm; (**c**) 22.0 mm; (**d**) 26.4 mm.  
and strain in the pipeline, accelerating its failure process. After shell buckling failure occurs, a pipeline without internal pressure will have local inward depressions of the pipe wall, while a pipeline with high internal pressure will have local outward protrusions of the pipe wall;
4. As the wall thickness decreases, the critical displacement necessary for pipeline failure gradually decreases, and the ability of pipelines to resist deformation significantly decreases. The point of pipeline wall failure will be closer to the fault displacement surface. If the wall thickness of the pipeline is too small, it may cause the entire pipeline to be in a fragile and easily damaged state under internal pressure.  
Conceptualization, R.Z. and S.L.; methodology, R.Z.; software, C.W. and S.L.; validation, S.L.; formal analysis, R.Z.; investigation, J.Z.; resources, W.L.; data curation, C.W.; writing--original draft preparation, R.Z.; writing--review and editing, R.Z.; supervision, R.Z. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Shandong Provincial Natural Science Foundation (Grant No. ZR2019 MEE099) and National Natural Science Foundation of China (Grant No. 51408609).  
Not applicable.  
The authors declare no conflict of interest.