Experimental study on the tensile performance of circumferential joint in shield tunnel

Abstract

When a shield tunnel is subjected to earthquakes and longitudinal deformation of the stratum, the segment ring may open along the longitudinal direction, thereby rendering the circumferential joint more vulnerable when being pulled. In this study, a self-made loading device was adapted to analyze the mechanical characteristics and failure process of a circumferential joint with a straight bolt in a large-section shield tunnel during the drawing process. The tensile performance was measured through tests with a 1:1 joint to study the behavior of the circumferential joint, including the strain distributions of steel fiber-reinforced concrete (SFRC) and reinforced concrete (RC), bolt stress distribution and transmission, structural acoustic emission (AE) and microscopic information of the segment concrete, and final failure mode of the joint under different load conditions. Results show during the drawing process, the circumferential joint with a straight bolt affects the stress distribution on the circumferential joint surface and the area of the hand hole on the inner surface of the segment; however, the circumferential joint has negligible effect on the outer surface of the segment. Although the straight bolt is always in a favorable working condition, segment failure is inevitable for both SFRC and RC segments. In addition, the damage zone expands mainly from the bolt hole on the joint surface to the hand hole on the inner surface. During the tensile process under cyclic loading and unloading conditions, the segment exhibits cumulative damage, and the Felicity effect can be verified using AE technology. In summary, the steel fibers improve the tensile strength and crack resistance of circumferential joints under high-strain conditions.