A large diameter 30-year old buried jointed pre-stressed pipeline which has been designed according to AWWA was subjected to a recent earthquake. It is suspected that the pipeline has developed cracks. How many of them must be exhumed to prove with 95% confidence level one way or other? And why.
The alternative is to monitor leaks and hope that leaks come before the burst.
WE need only one piece of a jointed pre-stressed pipeline to be exhumed if the surrounding geology doesn't change.
The pipeline is assumed to consist of a continuum of several sections, each with its own resistance to axial or bending stress; under seismic conditions, it is possible to evaluate the different vibrating modes, with related circular frequencies and contributing factors. Such evaluations allow rotations and maximal displacements to be determined in each joint. Nevertheless, experience proves that, after an earthquake, cracks and fissures occur on the rim of the "bell", such that the pipeline operation is stopped.
To evaluate the effects of an earthquake on an underground pipeline. we examine the motion of the land. whose effect is felt over an extensive area. Pipelines are thus analyzed as mono-dimensional structures, consisting of several sections connected with various types of joints, subject to ground movement and with variable characteristics along their course.
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