Response of pipelines of differing flexural stiffness to normal faulting

Relative ground movement represents a severe seismic hazard to pipelines crossing faults, and the maximum expected pipeline strains are the primary design concern. Past research has documented how stiff steel pipelines respond to permanent ground deformation and has produced calibrated empirical models of pipeline response to strike-slip and normal faulting. However, what little data exist on flexible pipelines illustrate how ‘stiff pipeline’ soil reaction models significantly overestimate peak strains for flexible pipelines. Results for four centrifuge tests conducted on model pipelines are presented to quantify the flexural response of pipelines to normal faulting over a wide range of pipeline stiffness. Continuous functions of pipeline and soil displacement calculated using digital image correlation are used to assess pipeline curvature, soil reaction and relative displacement. Comparisons of peak measured curvatures to current design analysis methods confirm that empirical stiff pipeline soil reactions progressively overestimate maximum curvature as the pipeline's stiffness decreases. Two strategies to modify current empirical soil reactions to account for flexible pipelines were then investigated, with the strategy of reducing the stiffness of the empirical soil reaction (while maintaining the advantage of a simplified, abrupt, step-like fault) providing better outcomes than modification to account for more realistic ground displacement profiles.