Seismic Design Criteria for Underground Pipelines

The current design practice for water/sewer lifelines does not take seismic loads into account. Note that the design of buried pipelines for seismic excitation is not necessarily governed by the strength of the system, but is governed by its flexibility or ductility. For evaluation of existing piping systems, as well as future design application, the purpose of this paper is to define the reserve strengths and reserve ductilities of a buried pipeline beyond its normal stress/strain conditions. By comparing the reserve strains/curvatures to the imposed ground strains/curvatures, the safety of a given pipeline can be studied. Hence, the studies of current design practices and ultimate failure criteria are essential. One may note that in designing buried pipelines, corrosion tolerance is added to the required thickness. With the passing of time, the corrosion tolerance thickness is reduced. Thus, the reserve strength/ductility calculated for seismic resistance will also vary with time.