Influence of Joint Stiffness on Three-dimensional Deformation Mechanisms of Pipelines under Tunnel Active Face Instability

Although extensive research has been conducted in literature to investigate tunnelling effects on pipelines, the performance of existing jointed pipelines subjected to excessive tunnel movement has not been investigated. This study sets out to examine the effects of tunnel active instability on three-dimensional deformation patterns of existing pipelines using physical model tests. Tunnelling induced ground / pipeline settlement, joint rotation, and bending strain under various horizontal tunnel face movements are systematically explored. Results show that the tunnel face pressure at the active limit state is practically independent of tunnel cover to diameter ratio (C/D). Existing pipelines that fall within a range of 0.1 D ~ 0.5 D ahead of the tunnel face experience excessive settlements, significant bending strains and joint rotation. The measured peak settlement of pipelines at 0.3 D in front of the tunnel face exceeds the allowable limit, and the maximum settlements in the jointed pipeline are up to 2.67 times those observed in the continuous pipeline. Meanwhile, the joint rotation angle and settlement induced in the jointed pipeline are greatly affected by the C/D ratio and decrease by up to 55.5% and 22.0% with an increasing C/D ratio from 1.0 to 1.5.