The radiation characteristics of seismic waves provide guidance for improvement of acoustic techniques for locating buried pipelines. Two fundamental excitation approaches have been proposed over recent years, which involve direct pipe excitation and ground surface excitation, with the latter having a wider range of applications since it does not require the access point on the exposed pipe. Three possible surface exciters on an elastic half space are studied by using the steepest descent method and their performances in relation to radiated shear wave are of particular interest in this paper. Comparisons of the energy partition and directivity patterns of the resultant seismic waves are made with respect to Poisson's ratio. It is found that vertical excitation leads to the energy mainly distributed on the surface Rayleigh wave, especially in the case of low Poisson's ratio, whereas horizontal excitation gives rise to the largest energy of shear wave. This is in accordance with the well documented results. For torsional excitation, only the shear wave is generated; however, the main lobe is in the direction parallel to the ground surface. Numerical results show that horizontal excitation may offer the best performance, allowing optimization of its performance for practical pipe location.
展开▼
