The Pipeline Design Method Against Large Fault Displacement

Abstract

This study proposes “water pipeline system and design method with Earthquake Resistant Ductile Iron Pipe (ERDIP) against fault displacement”. ERDIP pipeline can absorb the large ground displacement at the event of big earthquakes by the joint movement (expansion, contraction and deflection) and the joint locking system. Though the ERDIP pipeline has many experiences of big earthquakes such as the 1995 Kobe Earthquake, the 2011 Great East Japan Earthquake, no documented failure has been reported for 40 years. In case of fault crossing pipeline, there is a possibility for relative displacement of several meters between the pipeline and ground, locally, to occur. This study examined the ERDIP pipeline design to withstand strike-slip fault by FEM analysis with shell element of 1500 mm ERDIP and spring elements which are modeling soil and ERDIP joint. ERDIP pipeline can accommodate about 2m fault displacement by the joint expansion/contraction and deflection, and keep the stress in the pipeline within elastic limit. The additional countermeasure should be required when the fault displacement is over 2m because the pipeline could be stressed beyond the elastic limit. As a countermeasure of over 2m displacement, it is effective to use “Large displacement absorption unit”, which can expand/contract 10 times compare to ERDIP joint and absorb the locally-concentrated axial displacement of pipeline. We confirmed that ERDIP pipeline with “Large displacement absorption unit”, which is named “Large displacement absorption system”, can accommodate more than 3m fault displacement within elastic range stress of the pipeline. We established the optimized layout of “Large displacement absorption unit”. We also established the design method using several “Large displacement absorption unit” when we can’t identify exact fault location, but the fault lies within the range of pipeline location.