Abstract: The underground pipelines are connected by socket joints, and the continuity of the pipeline depends on joint rigidity. However, previous studies mainly simplified pipelines as continuous structures, and the effect of joint rotation on pipeline deformation mechanisms was ignored. By conducting centrifuge model tests and two-stage numerical parametric studies, tunneling-induced deformation mechanisms of pipelines with different joints stiffness are explored in this study. Because of the existence of flexible joints, overall flexural stiffness of jointed pipelines is much smaller than that of continuous ones. Moreover, tunneling-induced joint rotation results in jointed pipelines to have a better ability to deform with surrounding soils. Thus, tunneling-induced settlement in jointed pipelines is much larger than that of continuous pipelines. By simplifying jointed pipelines as continuous structures, tunneling-induced pipeline settlement is grossly underestimated. A linear relationship between the joint rotation angle and volume loss is observed. Based on parametric studies, a dimensionless group of relative pipeline-soil stiffness is established to differentiate relatively rigid and flexible pipelines. Calculation charts between the relative values of the length of pipe segment, pipe-soil stiffness and joint rotations are established for relatively rigid and flexible pipelines, respectively. Centrifuge test results are used to verify the proposed calculation charts. The proposed method can effectively predict the joint rotation angle due to tunnel excavation. Research finding from this study can be used in underground pipeline network reconstruction projects in urban cities.

Key words: centrifuge modeling, tunnel excavation, jointed pipelines, joint rotation, prediction method