Acoustic wave propagation in buried iron water pipes

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Abstract
A study of the possible axisymmetric modes that propagate at low frequencies in buried, water‐filled iron pipes is presented. It is well known that for a vacuum‐pipe‐vacuum system the sole non‐torsional axisymmetric mode that exists at low frequencies is the fundamental L(0,1) mode. When a pipe is filled with water and still surrounded by a vacuum it is also known that another mode then appears, which at low frequencies is characterized by predominantly axial water‐borne displacements. In addition to these modes, this paper explores two other, less‐well‐known axisymmetric modes whose existence depends on the acoustic properties of the outer medium that surrounds a pipe. The predicted characteristics of these modes are presented; the likelihood of them propagating over any significant distance in a buried water pipe is discussed, followed by an experimental validation using measurements on water mains in urban areas of the UK.