Failure Mechanisms in Pipelines Bridging a Void

An experimental testing program is being conducted to evaluate the failure mechanisms of pipelines subjected to a localized loss of support. The program involves a series of centrifuge tests conducted to evaluate the response of pipes embedded in sand backfill and placed over a rigid trapdoor base that is released during testing. The tests involve a pipe with prototype diameter of 1.1 m and a soil cover height of approximately 5 times the pipe diameter. Failure patterns are observed along longitudinal and transverse cross-sections of the pipe-soil system. The influence of pipe stiffness and backfill density on the behavior of the system is preliminary assessed in this paper. The transverse sections showed the development of well-defined slip surfaces initiating at the edge of the void. Slip surfaces did not develop along the longitudinal cross sections. The mode of failure of flexible pipes involved buckling in the shoulder of the pipe and a reversal of curvature at the invert due to excessive deflection. Preliminary test results indicate that the density of the surrounding soil has a significant effect on the damage experienced by flexible pipes