Many energy pipelines traverse hilly and mountainous terrains that are prone to landslides and other geohazards. The mapping, identification, and monitoring of geohazards along pipeline right-of-ways are essential in effectively managing the risks they may pose to pipeline integrity and human safety. One approach to monitoring potential geohazards is to use space-borne synthetic aperture radar (SAR). SAR is an effective and proven technology used to monitor ground surface change over vast areas and can be used in a cost-efficient manner, especially in areas that are remote or challenging. This paper focuses on aspects of a novel three-fold approach for monitoring geohazards using satellite radar imagery. This is accomplished by combining interferometric SAR (InSAR), automated amplitude change detection, and polarimetric change detection. The resulting analyses are to be merged into a new geohazard index map that will provide a simplified overview of the change influence for given pipeline segments over an extensive area. It is anticipated that the geohazard index map would be used to support operator decision-making in proactively mitigating the potential adverse effects identified. A brief introduction to the methodologies employed and a discussion of the validation that is currently underway as a joint project between MDA Geospatial Services and Southern California Gas Company is provided by this paper.

This paper summarizes key considerations in guidelines published in early 2009 that were developed through a Pipeline Research Council International, Inc. (PRCI) supported by PRCI, the Pipeline Hazardous Materials and Safety Administration of the Department of Transportation, and the California Energy Commission. Past practices for pipelines, as well as almost all other construction projects, have focused on avoidance of areas that have a reasonable probability of experiencing geohazards (defined as large ground displacements that may arise from slope failure, slope creep, earthquake triggered slope movement, and subsidence). This approach has been generally successful when there are limited restrictions on selecting a pipeline alignment. Avoiding potential geohazards is becoming increasingly difficult because of the inability to obtain landowner agreements, the lack of space in common utility corridors, environmental restrictions, incompatibility with existing land use, and/or public opposition. In route corridors where geohazards cannot be avoided, the potential risks associated with these hazards must be managed. Pipeline integrity management strategies to mitigate geohazards consist of: (1) design measures that improve the pipeline resistance to the geohazard, (2) measures that limit or control the severity of the geohazard, and (3) operational programs to monitor ground displacement or pipeline response and identify conditions that may warrant further engineering investigations or mitigation activities. Identifying the most appropriate mitigation strategy needs to be based upon specific hazard scenarios and operating circumstances. The PRCI guidelines provide recommendations for the assessment of new and existing natural gas and liquid hydrocarbon pipelines subjected to potential ground displacements resulting from landslides and ground subsidence. One of the most significant benefits of the guidelines is the systematic approach developed for managing pipeline risks from landslide and ground subsidence hazards. It is hoped that this approach, presented in detailed flow charts, will lead to improvements in current practices by providing a common framework for pipeline operators, the local, state, and federal agencies that have regulatory oversight, and the general public to engage in discussions regarding potential risks from pipelines in areas of unstable ground and the most effective and practical means to reduce those risks to an acceptable level.

Landslides are often a hazard to high-pressure gas transmission pipelines operating in hilly and mountainous terrain. Typical mitigation options include pipeline rerouting or removing the landslide from the pipeline, if possible. When rerouting or hazard removal is not a viable option due to terrain conditions or the size of the landslide loading the pipeline, directional bores can be used to place the pipeline beneath the active portion of the slope failure. As part of our study of the geotechnical viability of mitigation options for a pipeline impacted by coastal landslides, rerouting and landslide mitigation alternatives were fully investigated. Geologic interpretation of high-resolution, publicly available IfSAR and privately-flown LiDAR data were used to evaluate alternative routes around active and potentially active landslides. Geotechnical borings through the landslides ultimately provided sufficient information supporting directional drilling beneath the active landslides as the most efficient alternative, returning the pipeline to full service.

Guidelines for the seismic design of oil and gas pipelines have not been updated in a single reference document since 1984, when the American Society of Civil Engineers released their publication, Guidelines for the Seismic Design of Oil and Gas Pipeline Systems. Since 1984, substantial progress has been made in identifying and quantifying seismic hazards, understanding pipeline response under large, displacement-controlled strain conditions, and analytical methods for assessing pipeline response to permanent ground displacement. In 1998, the Pipeline Research Council International, Inc. (PRCI) initiated a project to update seismic design guidelines for pipelines with the goal of incorporating advances in current engineering practice since the early 1980s and to create a document that can be regularly updated to take advantage of new research findings. The PRCI project to develop the guidelines was undertaken by two investigators heavily involved in the 1984 American Society of Civil Engineers guidelines. Two teams of independent expert reviewers were used during the project to assure the recommended practices were technically consistent with the current state of knowledge of seismic hazard assessment, pipeline behavior, and analysis methods.

Field bends in large diameter pipe are routinely used in the construction of oil and gas pipelines. Mild ripples along the intrados are often unavoidable where such bends have a high D/t or high yield strength. Present regulations and industry standards differ in their treatment of mild ripples, consequently, the acceptance of such features has been heretofore inconsistent. A review of prior work on the subject was undertaken. Shell finite element analysis was then used to estimate the effect of ripple magnitude and spacing on stresses due to pressure and bending. Stress concentration effects were used with a suitable fatigue damage rule to estimate the effect of ripple parameters on service life. Results were benchmarked against the available test data.

Ground displacements, strains, and tilts can be calculated by repeated measurements of the lengths of six chords and relative elevations of an array of four points, known as a quadrilateral. Quadrilateral measurements allow ground-surface deformation and strain to be calculated. Typically, soil-pipeline interaction results in pipeline strain being less than ground strain. Strain gauges traditionally have been used on pipelines in landslide areas to aid in managing pipeline risk. Quadrilaterals may be economical alternatives to placing strain gauges on existing pipelines in areas of active or potential slope movements. A threshold ground deformation or strain is used to trigger more expensive means of evaluating pipeline integrity. Quadrilaterals are relatively inexpensive to install, but must be carefully located and founded deep enough to avoid seasonal shrink-swell effects of the soil. Measurements must be taken with precise instruments (tape extensometer) so that small changes can be detected with acceptable errors. Three contiguous quadrilaterals were installed in Spring 2003 in a landslide-prone area of southern California to aid in monitoring a slope between the main scarp of a recently active landslide and a pipeline bridge foundation. Engineering geologic evaluation supported a conclusion that the rate of headward crest advancement would be slow, but a method of detecting and quantifying slope deformation was needed for operational risk management.