Chapter 13 CREATION AND MANAGEMENT OF A LANDSLIDE AND EROSION GEOHAZARDS INVENTORY FOR NATURAL GAS TRANSMISSION PIPELINES IN CALIFORNIA
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Published:2020
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ABSTRACT
The Pacific Gas & Electric Company (PG&E) natural gas transmission system consists of approximately 6,800 miles of gas transmission pipeline traversing nine of the eleven unique geomorphic provinces of California. In this dynamic geologic environment, it is inevitable that extensive linear assets such as gas transmission pipelines will be affected by geohazards such as landslides and erosion. Geohazard-related ground movement can result in increased bending strain which in turn can lead to permanent pipe deformation and possibly failure. Asset owners must therefore develop strategies for assessing and managing these geohazards and associated asset risk.
This paper provides an overview of the creation and management of the PG&E Transmission Integrity Management Program (TIMP) Geohazards Program which was developed to assess and quantify exposure of gas transmission assets to landslide and erosion systemwide. The Geohazards Program has, to date, inventoried approximately 14,000 landslide and erosion sites along PG&E gas transmission pipeline corridors. Geohazard sites are identified, evaluated, ranked, and managed via a phased approach consisting of: 1) detection and desktop assessment; 2) initial field assessment and ongoing monitoring; 3) detailed site-specific study; and 4) mitigation, if necessary. This program utilizes a suite of detection techniques including geomorphic analysis of Light Detection and Ranging (LiDAR) data, change detection assessment from repeated LiDAR surveys, and correlation of geohazards with in-line inspection (ILI) data for bending strain; all in addition to traditional methods of geohazard detection such as periodic aerial and ground patrols.
Well curated geohazard inventories support risk reduction and asset management efforts by providing a tool for systemwide prioritization of geohazard mitigations. Improved early detection and prioritized mitigation of geohazards allows for increased proactive asset management and is expected to reduce the need for reactive response, leading to increased public safety and cost savings. The ultimate goal of this program is to develop and maintain a comprehensive geohazard inventory that will support more accurate and reliable characterization of asset risk by providing quantification of geohazard exposure. This, paired with future efforts to quantify associated asset fragility, will allow further development of a quantitative risk-based approach for asset management.