Research on displacement analysis and control measures of shield tunnels for long-distance pipelines crossing rivers

Objective To solve the problems of excessive floating displacement and stress concentration of pipelines in the crossing section of river tunnels under internal and external loads, it is necessary to clarify the causes of damage and deformation of pipeline ancillary facilities and take treatment measures. Methods Taking the treatment of pipeline displacement hazards in the crossing section of a certain river tunnel as an example, in view of the current situation of broken support bolts and excessive pipeline displacement, treatment measures such as stress release and bolt repair were carried out. The finite element method and pipeline stress and displacement monitoring technology were adopted to carry out stress assessment, dynamic monitoring and data analysis of the gas transmission pipeline under the action of temperature difference, conveying pressure and buoyancy. Results The research results show that: With the damage of the piers in the water-filled state, the maximum stress of the pipeline under the operating conditions and design conditions is 300.2 MPa and 334.2 MPa respectively, and the pipeline is at a high stress level. After pumping water, the stress of the pipeline decreased significantly, with the maximum values being 171.46 MPa and 214.67 MPa respectively. To prevent similar displacement hazards in the pipeline from occurring again, countermeasures such as stress release, bolt repair and corrosion control, tunnel leakage repair, and annular support reinforcement of the pipeline have been implemented. On this basis, monitoring of pipeline stress and displacement was carried out. Relying on the monitoring data, the stress level and displacement state of the pipeline during the post-treatment period and the winter supply guarantee period were clarified. Conclusions The fracture of the support bolts is the risk cause of the hidden danger in this case. The water buoyancy load is the direct cause of the excessive floating displacement of the pipeline. The research results provide practical guidance for solving the risk management problem of shield tunnels crossing oil and gas pipelines, and can be used as a reference for the operation decision-making of tunnels crossing pipelines.