Abstract: The conventional shield launching technology currently is accompanied by multiple risks and drawbacks, including suspended assembly of the negative ring segments and segment roundness, settlement, and inclination induced by empty propulsion. These enlarge self-weight and spatial effects of large-diameter shield tunnel segments, posing greater challenges. To address such technical challenges and risks, based on the development trends of innovative segment structural design and automatic rapid assembly, an innovative launching technology featuring rapid assembly and propulsion of negative ring segments without back-push is proposed. The proposal is verified through theoretical simulation, calculation, and field tests implemented in a number of practical projects. The detailed construction steps are described as follows: (1) Prior to assembling the negative ring segments, shape steel bracing with designated lengths is installed and welded on the reaction device with high precision, extending the bracing to the shield tail reinforcing ring. (2) The negative ring segments are assembled at preset positions inside the shield tail. During the assembly process, the thrust cylinders and shape steel bracing are fully used to compact each segment of the full ring in sequence. (3) The friction of the shield body or additional resistance applied result in a stable force transmission structure for all segments under empty propulsion, thus enabling rapid assembly of negative ring segments and shield launching. Research results indicate that shape steel bracing with appropriate length, cross-section, and axial force enables rapid ring formation of the negative ring segments, realizing continuous negative ring segments assembly and shield propulsion without thrust. 

Key words: shield tunnels, negative ring segments, rapid assembly, segments with no back-push, propulsion and launching, shape-steel bracing