Experimental study on mechanical behavior of the skew joints of shield tunnels under large eccentric compressive loading: Fid-Bau Portal

Experimental study on mechanical behavior of the skew joints of shield tunnels under large eccentric compressive loading

Zhang, Jinfeng / Zhao, Ming

Abstract

Highlights • Three-segment local structure with two skew joints in shield tunnels was tested. • Specimen showed local compression failure under PBM and bending failure under NBM. • Skew joint opening angle can be obtained through the addition of segmental rotation angles. • Skew joint revealed a phenomenon of strain advance and strain lag.

Abstract The existence of joints in shield tunnel lining rings contributes to various deformation problems, such as leakage, joint opening, cracking and dislocation, which will severely impair the safety and durability of tunnel structures. Laborious experiments having tried to work out the mechanical properties of joints, none have drawn attention to two special segmental joints existing in Shanghai metro shield tunnels, which are obliquely intersecting the frontal plane of the lining ring and thus appear askew compared with the rest. The study investigated segmental specimens with the K-shaped top block and its two adjacent segments, including two skew joints connected using straight bolts. Given two groups of experiments, their mechanical behaviors throughout the failure process when subject to a positive and a negative bending moment showed that the bending moment’s impact on bolt strain, joint opening and segmental rotation could be illustrated by two stages when the bending moment was positive and four when negative. Besides, the joint compression height slightly decreased under both conditions and tended to be stable after bolts yielded when subject to a negative moment. The joint opening angle was proved equal to the sum of the segmental rotation angles from both sides of the joint, indicating the individual segment could be regarded as a rigid body. Moreover, the maximum joint opening width increased linearly with the joint opening angle, so did the deflection at the joint position with the segmental rotation. Above all, the skew joints examined behaved similarly to but differently from those of straight joints as there happened strain advance of the bolt and the concrete at one side and strain lag at the other side, which would probably become more obvious as steeper the oblique angle of the skew joints grew.