Effect of Geohazards on Pipelines
PHOTO OF A BUCKLED TRANSMISSION PIPELINE FROM LAND SUBSIDENCE
When planning a pipe route or evaluating an existing one the associated geohazards along that one should be considered. Those which are most commonly considered geohazards are landsliding, land subsidence from underground mining or karst, and earthquake induced ground motions (i.e., faulting, liquefaction, lateral spreading and landsliding). This can determine whether that investigated route is viable or not. Given the long line reaches, the operator can struggle with determining which areas along the alignment contain the most critical geohazard(s). Whether along a proposed or existing route is best done by a two-phased approach. Phase 1 would identify those geohazard areas that can affect the pipeline during its lifetime, and Phase 2 would identify those geohazard areas which may potentially exceed the operator’s acceptable risk threshold.
The first step when evaluating the vulnerability of the pipeline to a geohazard is the assessment of the event (or occurrence) and severity probabilities (or in other words, what is the chance of a certain magnitude of ground motion). However, even more important is the assessment of the behavior or damage potential of the pipeline to the concerned geohazard movement that could occur during the expected operational lifetime of the line. The key overall assessment here then becomes whether the determined damage potential (occurrence and associated severity probabilities) exceeds the threshold of acceptable exposure level by the operator/owner. Evaluating the damage potential of certain site conditions many times requires numerical analysis in order to account for all the important ground movement, backfill, and pipeline conditions.
For any geohazard condition, the damage analysis should consider the primary modes of pipeline deformation, which are tensile stretching, buckling and bowing (aka upheaval buckling). These pipe deformations are a function of the nature of the ground movement the pipeline is exposed to. For example, significant tensile and compressive deformations can result from differential vertical (settlement) and lateral ground movement perpendicular to the pipeline, as well as, slippage between the ambient backfill and the line from lateral ground movement along the pipe.
PHOTO OF A TRANSMISSION PIPELINE THAT BOWED OUT OF THE GROUND FROM LAND SUBSIDENCE
Where the risk is deemed too high, there are many ways to mitigate the damage or hazard potential, these include:
• Relocating the line; • Telemetric monitoring of pipe deformations; • Designing for the ground movement; • Reducing the backfill/pipe friction/adhesion against slip; • Using restraints against upward bowing; and • Installing stress relief joints.More information on this topic can be obtained from below.
BLOG: How to Handle Geohazard Risks Engineering UPDATE Issue #4 entitled: Improvement of Mine Support Saves Pipeline from Subsidence event Engineering UPDATE Issue #25 entitled: Transmission Pipeline Subsidence from Mining Engineering UPDATE Issue #44 entitled: Property Management System for Geotechnical Risks Engineering UPDATE Issue #51 entitled: Upheaval Buckling of Pipelines
