INNOVATION March-April 2014

f ea t u r e s

This geohazard assessment approach has evolved and has been extended for quantitative risk assessment, using estimated susceptibility as a surrogate for probability of annual loss of containment. The assessment framework is proscribed in the sense that all geohazards are assessed through the same set of partitioned variables, allowing the assessment results from individual geohazards to be combined into an overall geohazard susceptibility profile. In assigning values to each of these parametres, sound engineering judgment is required. Estimates must be considered valid to an order-of-magnitude given the general paucity of information at early stages of a project. Improved estimates of parametre values are possible as more detailed route information is acquired. Different methods can be used to estimate parametres, such as detailed numerical modelling where site-specific infor- mation is available, general empirical relations where only basic route information is available and engineering judgment where little information is available. Continuous Improvement Conducting a baseline assessment, assuming unmiti- gated conditions (i.e., standard design with no spe- cial design segments), will aid in engineering design optimization. This assessment identifies segments where calculated susceptibilities exceed a selected threshold. Then, preliminary mitigation options for these segments are considered to reduce susceptibility to an accept- able value. This process provides an initial estimate of mitigation requirements, but is not a substitute for good engineering judgment. Other issues such as pipe expo- sure, construction-related mitigation and environmental effects are also considered as part of the overall engineer- ing design process. Several iterations of geohazard assessment may be undertaken during the conceptual, preliminary and detailed engineering phases of a pipeline project as the route and other design concepts are finalized. Post- construction conditions can be used to update the geohazard assessment as part of an Operational Integrity Management Plan. In conclusion, pipeline geohazard assessment is an important component of new pipeline projects and results can then be combined with other hazard assessment results, as required, to provide an overall risk evaluation for a pipeline. Flexibility in methods used to assess specific assessment parametres within a transparent and consistent prescribed framework is the strength of the approach. Dr. Rodney S. Read, P.Eng., P.Geo., P.Geol., works at RSRead Consulting Inc, in Okotoks, Alberta. Moness Rizkalla, P.Eng., works at Visitless Integrity Assessment in Calgary, Alberta. Dr. John J. Clague, P.Geo., FGC, works at the Centre for Natural Hazard Research at Simon Fraser University in Burnaby, BC.

Historical Perspective The Mackenzie Gas Project is an example of a major Canadian pipeline project that included geohazard assessment as part of the engineering design. The semi- quantitative approach developed for the project involved an inventory of 31 credible, probable geohazards—both common geohazards such as landslides and less common ones such as frost heave and thaw settlement—under eight general categories. The National Energy Board concluded that the approach was a suitable design tool for the detailed design phase of the project. A strategy was adopted to separate the likelihood of geohazard occurrence from the effects of the geohazard, should it occur, on the element at risk (in this case, it was the pipeline system). Geohazard likelihood was partitioned into three parametres occurrence—certainty, frequency and development rate—to estimate the likelihood of occur- rence of each specific scenario. A separate vulnerability parametre was used to estimate the expected effect of a geohazard occurrence in relation to the pipeline system, accounting for the pipeline’s capacity to withstand relatively minor geohazard occurrences such as shallow slumping or erosion. Vulnerability assessment accounts for soil-pipe interaction and facilitates pipeline design optimization.

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