This case study summarizes the successful implementation of a team approach to geohazard identification and mitigation. The Owner/Operator worked with Golder to establish a system-wide geohazard pipeline integrity management approach. The first part of the program included a phased geohazard assessment along the right-of-way. The second part of the program included office and field-based training provided to the local Pipeline Operations Staff, on how to identify geohazard features. Golder initially identified and delineated a landslide based on February 2018 lidar data (Phase 1). A ground reconnaissance (Phase 2) was completed in November 2018, which showed the landslide had expanded approximately 12 feet downslope since the lidar data had been collected. Local Operations Staff identified possible additional movement in February 2019. Subsequent field-mapping confirmed an additional approximately 15 feet of downslope movement between November 2018 and February 2019.

 

Due to the active movement, additional assessments were completed to further characterize the landslide and the possible threat to the pipeline. A review of historic aerial imagery and Operator data revealed this site had been previously mitigated multiple times. A geotechnical subsurface exploration program consisting of dynamic cone penetration (DCP) tests suggested the landslide depth was such that the pipeline was likely engaged by the ground movement. A comparison of as-built survey versus current pipeline location survey was completed, which showed approximately a 3-foot deviation from the as-built location, indicating possible pipeline strain. The Owner/Operator worked with the Center for Reliable Energy Systems (CRES) and Golder to evaluate the threat of observed pipeline strain and the possibility of additional landslide movement. This analysis showed the observed strain to be less than 30-percent of the threshold of concern (“warning level”). Thus, it was opted to postpone implementation of mitigation measures until seasonally drier conditions persisted, in order to avoid the negative impacts and inefficacies of winter or spring construction. Additionally, targeted mitigation along the site was deemed suitable rather than large-scale strain relief excavations.

 

The mitigation measures were implemented in May-June 2019 and Golder worked with the Owner/Operator and Contractor to target site-specific mitigation measures based on the observed ground conditions during construction. The mitigation consisted of excavation below the pipe depth and installation of targeted drains at multiple locations across the site, as well as general grading to control the surface water flows and restore the right-of-way. During the excavations prior to drain installation, vibrating wire strain gauges were installed on the pipe for continued monitoring. Following site restoration, the strain gauges were connected to remote monitoring units to provide real-time strain readings of the pipe. The Owner/Operator continues to monitor this site, post-mitigation.


Case Study of Team Approach to Geohazard Identification, Characterization, and Mitigation

Division / Sponsors: 
Pipeline Systems Division

Paper Proceedings: https://asmedigitalcollection.asme.org/IPC/IPC2020/volume/84447

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