Abstract: In response to the difficulties associated with managing deformation in the construction of large tunnels,we have devised an innovative steel frame joint with multiple pressure-relieving stages.This joint has been specifically designed to accommodate tunnels that undergo substantial deformation.This joint functions as an autonomous element that connects steel frames,incorporating a pressure-relieving mechanism.This mechanism effectively absorbs energy from the surrounding rock,thereby preventing distortion of the steel frame and preserving the overall structural integrity of the steel arch.The design of the joint is characterized by a combination of structural simplicity and high effectiveness.Notably,it incorporates various advantageous features,including energy absorption,resistance to eccentric loading,constant resistance support,and multi-stage pressure relief.To evaluate its mechanical properties,we conducted a series of experiments,both indoors and numerically.These experiments focused on analyzing the joint’s performance under axial compression,resistance to eccentric loading,and its connection capabilities with steel frames.The results demonstrate that:(1)Our research reveals that by modifying the wall thickness of the collapsible sleeve,it is possible to attain multi-stage constant resistance.The results of axial compression displacement-load curve obtained by numerical test and laboratory test are consistent.(2)The operation of the joint can be divided into five stages:elastic deformation,plastic transition,initial pressure relief,enhanced pressure relief,and secondary stable pressure relief.(3)The key factors that influence the constant resistance of the joint include the wall thickness of the collapsible sleeve,the wall thickness of the extrusion sleeve,and the contact angle.(4)By setting a cross plate inside the retractable sleeve and a vertical post inside the extrusion sleeve,the pressure-yielding steel frame joint gains resistance to eccentric loading.Additionally,increasing the wall thickness of the extrusion sleeve effectively enhances the joint’s capacity to withstand eccentric compression.(5)The implementation of the pressure-relieving steel frame joint increases the allowable deformation of the steel frame structure by over 30 times,significantly enhancing its resistance to deformation.(6)When installed at different positions within the steel frame,the pressure-relieving effect of the joint is most pronounced at the arch foot,followed by the wall waist and then the wall foot.Moreover,increasing the number of joints enhances the steel frame’s resistance to deformation.In conclusion,our study on the structure and mechanical properties of pressure-relieving steel frame joints provides valuable insights for the design and construction of large-scale tunnels experiencing considerable deformation.