Effect of oblique bolt arrangement on flexural behavior of segmental joint for shield tunnel

Abstract

As the width of segments increases, segmental joints containing three oblique bolts are increasingly used while their flexural behavior is still not clear. Therefore, this paper presents a comprehensive investigation on the flexural behavior of such joints; and the effects of bolt arrangement are also highlighted. A series of full-scale experiments and numerical simulations are first performed to reveal the typical flexural behavior and failure characteristics of the joint with one single oblique bolt. Then, the verified numerical model is extended to investigate the influence of different oblique bolt arrangements (i.e. number and direction) on the joint flexural behavior under different axial forces. Five bearing stages can be identified during the whole loading process of joints, and they are separated by the bolts tension, concrete severe damage, contact of the segment top, and joint failure. Under small axial force, the joint failure under the positive moment is dominated by the tensile damage of concrete around bolt holes; while the compressive damage of concrete at the same position controls the joint failure under the negative moment. The concrete damage area changes to the compression zone as the axial force increases. The oblique bolt arrangement has little effect on the identification of five-stage bearing process of such segmental joints, but increasing the number of bolts can improve the flexural stiffness and ultimate bearing capacity of joints. Moreover, the joint containing three cross oblique bolts has a stronger flexural capacity than that containing three parallel bolts under small axial forces, which is because the change of the bolt direction avoids the connection of tensile damage zones around the bolt holes. However, these effects of bolt arrangement fade away as the axial force increases.