###### Abstract  
Research on the deformation characteristics and failure modes of buried pipelines under local suspension conditions caused by groundwater loss in coal mining subsidence areas is conducive to grasping the failure evolution law of pipelines and providing technical support for the precise maintenance of gathering and transportation projects and the coordinated mining of gas and coal resources. First, a test system for monitoring the deformation of pipelines under loading was designed, which mainly includes pipeline load application devices, end fixing and stress monitoring devices, pipeline end brackets, and stress-strain monitoring devices. Then, a typical geological hazard faced by oil and gas pipelines in the gas-coal overlap area--local suspension--was used as the engineering background to simulate the field conditions of a 48 mm diameter gas pipeline with a localized uniform load. At the same time, deformation, top-bottom strain, end forces, and damage patterns of the pipeline were monitored and analyzed. The results show that the strain at the top and bottom of the pipeline increased as the load increased. In this case, the top was under pressure, and the bottom was under tension, and the conditions at the top and bottom were opposite.. For the same load, the strain tended to increase gradually from the end to the middle of the pipeline, and at the top, it increased significantly more than at the bottom. The tensile force carried by the end of the pipeline increased as the applied load increased, and the two were positively correlated by a quadratic function. The overall deformation of the pipeline evolved from a flat-bottom shape to a funnel and then to a triangular shape as the uniform load increased. In addition, plastic damage occurred when the pipeline deformed into a triangular shape. The results of the investigation clarify for the first time the mathematical relationship between local loads and ultimate forces on pipelines and analyze the evolution of pipeline failure, providing a reference for pipeline field maintenance. Based on this, the maximum deformation of and the most vulnerable position in natural gas pipelines passing through a mining subsidence area can be preliminarily judged, and then the corresponding remedial and protection measures can be taken, which has a certain guiding role for the protection of natural gas pipelines. gravondwater loss; buried pipeline; subsidence impact; strain; failure pattern; subsidence area +
Footnote †: journal: Applied Sciences  
0000-0002-4300-3300][PERSON]  
0000-0002-333-3330][PERSON]  
0000-0002-3330-3300][PERSON]  
0000-0002-3330-3300-3300-3300-3300-33000-3300-3300-33000-3300-33  
When studying the phenomenon of surface movement and deformation in mining areas, it is found that the maximum surface subsidence in some mining areas often exceeds the actual mining thickness of coal seams [1; 2]. After the mining of coal resources, 'three zones' are produced, namely, a caving zone, a water-conducting fracture zone, and a bending subsidence zone [3; 4; 5; 6]. Affected by the development of the water-conducting fracture zone, the coal strata will have a hydraulic connection with the aquifer in the overlying rock and soil mass, causing the water level of the aquifer in the overlying rock and soil mass of the coal seam to drop [7], ultimately affecting the surface loose layer. The range of surface subsidence is expanding, and the amount of surface subsidence is excessive., which can easily lead to the local suspension of natural gas pipelines in the subsidence area. At this time, The stress on the pipeline's top, bearing the overburden rock and with a suspended bottom, can easily result in deformation and failure of the pipeline, which in turn leads to accidents such as leakage, poisoning, or explosion [8; 9; 10; 11]. Therefore, research on local suspended pipelines in the subsidence area is of great significance for mastering the stress and deformation characteristics of buried pipelines and their accurate and reasonable maintenance.