A Comparison of Lidar Change Detection Informed Buried Pipe Deformation Analysis to High Resolution IMU Survey Data

Abstract A highway widening project necessitated the reroute of a PG&E high pressure gas transmission line, resulting in a new pipeline alignment adjacent to a 155-foot-tall slope. Incipient slope failure, first observed as distress to the nearby highway, resulted in PG&E proactively reducing pressure in the section of pipeline believed to be within the nearby landslide mass. Several years of survey monitoring indicated that slope movement was ongoing, however, federal regulations require internal integrity inspections at regular intervals. These inspections require significantly higher pressure than was currently in the potentially distressed pipeline. Prior to increasing pressure for the inspection, PG&E performed an analysis to confirm that the creeping landslide mass had not compromised the pipeline integrity. This paper describes a project application wherein lidar cloud differencing calculation methods were used to develop estimates of vertical and horizontal ground movements profiles associated within the landslide along the PG&E gas transmission pipeline. Estimated ground movement profiles were used as inputs to buried pipeline deformation analysis models which were subjected to internal pressure and temperature differential loads. The models were used to develop estimates of along-pipe profiles of pipeline curvature, bending strains, axial and von Mises stresses and axial forces. The lidar-based estimated ground movement profiles were compared to pipeline geometry profiles measured during a recent high resolution IMU survey of the pipeline, as well as comparisons with the key pipeline deformation results estimated from the buried pipeline analysis models. This paper illustrates how the combination of lidar differencing calculation methods and buried pipe deformation analyses provided a reasonable comparison with IMU survey data. This project furnishes a unique example of how these technologies can be useful as an aid in decision making with respect to pipeline structural integrity considerations for geohazard induced permanent ground movements.