INNOVATION March-April 2014

Regulatory Guidelines According to CSA Standard Z662-11, it is the designer’s responsibility to assess geohazards and specify supplemental design criteria and mitigation techniques for pipeline loadings. This is done through the process of geohazard assessment. Results from an all-hazards assessment can be combined with consequence analysis to produce a risk assessment for a pipeline project. Options for hazard identification, frequency analysis and consequence analysis are listed in CSA Standard Z662-11 Annex B. These guidelines are flexible and allow fit-for-purpose qualitative, semi-quantitative and quantitative hazard assessment frameworks for geotechnical threats. Hazard control and mitigation decisions may be based on hazard assessment or risk assessment results, depending on the circumstances (CSA Standard Z662-11 Annex N). This flexibility is important as it allows immediate action to be taken in the event of a serious hazard situation that is identified, for example, during routine surveillance. Geohazard Assessment Approaches A variety of geohazard assessment methods have been developed in recent years. For instance, GIS-enabled, weights-of-evidence methods combine spatial data, typically using linearized empirical relations, to classify hazards. Published examples from Japan and elsewhere illustrate the use of stacked GIS data layers to estimate landslide susceptibility in areas with rela-

For example, empirical models require a sufficiently large calibration data set to cover all reasonably foreseeable combinations of parametres and tend to be more reliable in areas with relatively uniform geological conditions. Regardless of the hazard assessment method used, there are key considerations required to meet the intent of CSA Z662, including systematic, wholistic evaluation of geohazards within a defined assessment framework and a specific risk context. A common risk context is pipe integrity (i.e., loss of contain- ment), where the element at risk in this context is the pipeline. Other risk contexts can be considered, but a single risk context is necessary for consistent assessment of multiple hazards and to account for co- spatial geohazards that may represent trigger-event pairs or potential load combinations. Results from geohazard assessments focused on pipeline integrity may be used to inform other risk contexts related to environmental protection. While there are guidelines for evaluating some geohazard—for instance, landslides—for specific developments, professional judgment is required in order to apply these guidelines to pipeline projects. For example, assessment criteria in guidelines aimed at residential development or forestry practices may not be applicable without consideration of specific engineering design aspects of the pipeline system and planned mitigation.

tively uniform geological conditions. Mechanistic model-based methods use numerical models to relate variables affecting stability. These methods are most effective in situations where the numerical model is matched to in situ conditions and to constraints on instability, such as depth to bedrock. Hybrid methods combine elements of these two approaches to account for factors that may be difficult to incor- porate into a physics-based model. For example, mechanistic models of slope instability can be linked to rainfall through simplified infiltration models that account for changes in water table elevation. Each of these methods has its strengths and limitations, depend- ing on the type and quality of char- acterization data available and their distribution along the pipeline route.

Workers preparing sections of pipe for placement with side booms during construction of a natural gas pipeline.

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