Physical and numerical investigation of deformation mechanisms of jointed pipelines due to passive face instability of EPB shield tunnelling

The serviceability and safety of existing pipelines may be adversely affected by differential ground movements resulting from inappropriate control of face pressure of EPB (earth pressure balance) shield tunnelling. However, previous studies mainly concentrated on deformation mechanisms of continuous pipelines resulting from tunnel face active instability. In this study, 16 three-dimensional physical model tests were conducted to explore the effects of tunnel cover-to-diameter ratio ( C/D) and relative tunnel-pipeline position ( H/D) on deformation mechanisms of jointed pipeline due to tunnel face passive instability. Moreover, a systematic numerical parametric study was performed to develop calculation charts for estimating joint rotation angle subjected to ground heaves. For tunnel C/D ratios of 1.0 and 1.5, the existing jointed pipeline at 0.7 D and 1.2 D ahead of tunnel face experiences the highest heave and joint rotation angle, respectively. By increasing C/D ratios from 1.0 to 1.5, the maximum pipeline deformation decreases by up to 84.5%. A dimensionless group, namely relative pipe segment-soil stiffness, is proposed to distinguish relatively rigid and flexible jointed pipelines, and normalised pipe segment length and relative pipe–soil stiffness are also proposed to establish calculation charts for predicting joint rotation angles of relatively rigid and flexible jointed pipelines, respectively.