How do we Assess for Geohazards?

Many miles of pipeline around the world are subject to damage from geohazards.  As used here, ‘geohazard’ refers to any earth movements sufficient to damage a pipeline, and can also include weather- and water-related events that are potentially damaging.  So, we often group, under the heading ‘geohazard’, a wide range of phenomena such as:

  • landslide
  • subsidence
  • seismic events (faulting, liquefaction, etc)
  • aseismic faulting
  • flood
  • freeze
  • wind
  • wave action
  • buoyancy
  • seabed instability
  • bank erosion
  • scour
  • etc

Subcategories are often needed in order to efficiently manage multiple potential events at the same pipeline location.

The standard PoF triad of exposure, mitigation, and resistance efficiently measure this threat.

An interesting aspect of geohazard as an exposure–an ‘attack on’–pipeline integrity, is the distinction between measuring the geohazard event vs measuring its effect on a pipeline.  For example, the geohazard event could be ‘flood’, resulting in subsequent events of

  • scour,
  • bank erosion,
  • avulsion,
  • debris transport,
  • and others.

We often have published recurrence intervals for the primary and/or the secondary events.  These published frequencies are the first step in our estimates of the PoF attack frequency.  However, the events for which we really need a estimate of attack frequency are the integrity threats.  The pipeline-threatening events corresponding to the above list of geohazards are

  • lack of support (increasing the gravity loading)
  • buoyancy (creating an uplift force)
  • lateral loadings (from flowing current and debris)
  • oscillations (fatigue loadings)

These will be some fraction of the geohazard frequencies since not every geohazard event will generate sufficient forces to threaten the pipeline.