A SYSTEMATIC APPROACH FOR MITIGATING GEOHAZARDS IN PIPELINE DESIGN AND CONSTRUCTION

摘要

Pipeline projects are often faced with the challenge of balancing efficient design and construction with mitigation of potential hazards posed by low probability events, such as earthquakes and landslides. Though systematic characterization of geological hazards is sometimes perceived as an added project expense, failure to recognize and mitigate hazards at an early stage can lead to schedule delays and substantial liability, repair, and business interruption costs. For example, it is estimated that failure of the 660-mm Trans-Ecuador pipeline in the 1987 earthquake cost roughly $850 million in repairs and lost revenue. In order to minimize, mitigate, or avoid geological hazards, pipeline design projects can implement a phased investigative approach to refine route selection and develop parameters for detailed design. These studies provide information on geological conditions that progress from the general to specific and have associated uncertainties that decrease with increasing focus of investigations. A geohazard investigation for a pipeline project should begin with a Phase I "desk-top" study to evaluate regional geological conditions, establish a project specific information system, and make a preliminary assessment of landslide, fault rupture, liquefaction, geotechnical and constructability issues that will need to be considered in later phases of design and construction. Although the results of desk-top studies are limited and have large associated uncertainties, the initial results help to refine route selection and/or identify areas that may require hazard mitigation measures. Phase II investigations include acquisition of detailed corridor specific data such as topography and aerial photography, development of geological strip maps, and assessment of the pipeline corridor by an expert-level Terrain Evaluation Team (TET) with broad knowledge of geo-engineering issues. Assessment of the corridor by the TET results in recommendations for route refinement to avoid hazardous terrain, and identification of areas requiring detailed Phase III investigations. Phase III consists of detailed investigations of critical geohazard features to develop parameters for final design of hazard mitigation measures (e.g. fault crossing design). The geohazard features are characterized to determine permanent ground deformation (PGD) parameters such as location, geometry, amount and direction of displacement, and recurrence rates. Interaction with the pipeline design team should be continued through all three phases to maximize efficiency and ensure timely integration of results in route selection, refinement and design. Examples provided from projects in Turkey, California, and the Indian Ocean demonstrate the successful implementation of this phased investigative approach to characterizing and mitigating geohazards for both onshore and offshore pipeline projects. Implementation of this approach has resulted in significant project cost savings and reduced risk.