Buried Steel Pipeline Beneath a Surface Impact Close to a Pipe-Structure Interface

Abstract

For nuclear power plant life extension projects, safety related buried steel pipelines need to be assessed for the effects of postulated accidental impact loads. Examples of such pipelines include emergency firewater lines and control room vent ducts. Published solutions concerning the buried pipeline beneath a surface impact, often aim at a generic problem dealing with a pipe within a half space. The interface between the buried pipes and the underground structure is often ignored. In the case that a buried steel pipe penetrates into nearby underground structure in short distance from a surface impact, shear and bending may originate from reactions at pipe-structure interface, in addition to ovaling and buckling of the pipe section. Neglecting such boundary effect may lead to underestimating potential damage of buried pipeline, and jeopardizing the safety of the nuclear power plant. Comprehensive analysis of such structure-pipe-soil system is often subjected to availability of state-of-art finite element tools, as well as costly and time consuming. This study presents a simplified approach using basic concepts, in order to evaluate the buried pipeline beneath a heavy surface impact considering nearby pipe-structure interface. Applied impulse loadings for postulated surface impact are first established, followed by the evaluation of consequential vertical pressure directly on the top of the pipeline. The pipe cross-section is checked for ovaling and buckling. The closed form solution is then proposed to evaluate effect of pipe-structure interface.