Abstract: To more finely guide the structural design of largecrosssection specialshaped shield tunnel under the corresponding construction grouting load, a case study is conducted on the quasirectangular shield tunnel project of Ningbo metro line 3. The stress characteristics of the lining structure under construction load and grouting conditions are explored, and the real grout filling and diffusion processes and its pressure distribution law during synchronous grouting are investigated. Finally, a comprehensive analysis is conducted on the loading mode under grouting condition in the existing design model, the grout filling diffusion pressure distribution calculation model, and the pressure distribution pattern under special conditions. The results reveal the following: (1) The structural force is more uniform according to the grout filling and diffusion pressure analysis. (2) The structural force of the pipe is more unfavorable under grout filling conditions of the existing design model and load distribution under special conditions. (3) It is recommended to consider the structural force pattern corresponding to the grout circumferential filling and diffusion mechanism in the design model, and superimpose distributed pressures of 100 kPa, 150 kPa, 200 kPa, and 250 kPa at the crown, arch shoulder, waist, and bottom respectively.

Key words: largecrosssection specialshaped shield tunnel, grouting, structural stress analysis, load setting