Ground surface vibration due to axisymmetric wave motion in buried fluid-filled pipes

This paper is concerned with the ground surface vibration induced by the axisymmetric fluidborne wave motion in buried fluid-filled pipes. This wave has been exploited for water leak detection and, more recently, for the detection and location of buried pipes. Based on the model of wave propagation developed in recent work, this paper presents an analytical method for predicting the ground surface displacement resulting from the radiated elastic waves in the soil medium. It is shown that, for a sufficient large wavenumber-depth product, the radiated conical compressional and shear waves can be treated as plane waves incident upon the ground surface. Analytical expressions for the ground surface displacement are then given as the overall contributions from these incident waves and their reflections. Numerical simulations are further presented to predict the relative displacements normal and parallel to the ground surface under two representative pipe-soil boundary conditions, representing "perfect bonding" and "imperfect bonding". Theoretical predictions may help to explain some of the features observed in practice and hence offer a potential improvement over the current acoustic techniques for leak detection and pipe location.