According to international regulation and guidelines (i.e. UNI EN1998-4:2006; UNI EN1594; ASCE-ALA 2001; ASCE 1984) pipeline systems shall be designed and constructed in such a way as to maintain their integrity after seismic events in relation to the damage limitation state.
Evaluate seismic risk of a pipeline means combining an assessment of the earthquake-related geohazards and an analysis of vulnerability of the infrastructure to maximum expected actions.
In general, earthquake-related geohazards that may lead to pipeline damage are events associated to transient actions (i.e. ground-shaking) or to permanent ground-induced deformations (i.e. fault rupture; slope instability; soil liquefaction).
Seismic design of hundred-kilometres long gas transportation pipelines requires a characterization of the territory in a corridor buffering project line.
On these premises, Saipem has developed a multilevel approach to seismic design of gas pipeline systems starting from a general overview of hazards affecting the project corridor, up to detail the potential seismic issues concerning a single area.
This multilevel approach has been developed and applied for seismic design of gas transportation pipelines in high seismicity areas of Central Italy.
The first level of this approach is identification of seismic hazards interesting the whole corridor by way of studying available data and performing geological-geomorphological survey.
The outcome of this early stage provides location and, if possible, preliminary intensity of expected seismic effects for specific sites.
Subsequently, the hazard of these critical sites will be evaluated in detail with focused investigation survey and applying simplified methods (second level approach) or, if necessary, performing a deep analysis with advanced processes, such as computational simulation (third level approach).Once completed the earthquake-related geohazard analysis, pipeline vulnerability will be verified to the maximum expected actions (i.e. transient and permanent effects), by numerical modelling of structure response. Based on results of this verification, suitable mitigation measures will be developed.