The use of Rayleigh waves to detect the depth of a shallow landfill

Abstract

Abstract This paper describes a case study to determine the extent of shallow landfill on a site that was to be traversed by a new road. Pre-contract estimation of the quantities of landfill to be removed were required and, though the approximate lateral extent of the landfill was known, the depth was not. An opportunity therefore presented itself whereby measurements of the depth of landfill could be made using a non-intrusive geophysical technique and the subsequent excavation would allow the physical measurement of the actual depth of the landfill. The determination of the depth of shallow landfill using non-intrusive methods is difficult. Conventional surface geophysics needs high stiffness contrasts, consistent strata depths along the survey lines and experienced interpretation to achieve the best results. The Rayleigh wave technique offers the potential to obtain wave velocity against depth profiles at discrete points across a site so better enabling a section to be built up to show the extent of the landfill. The paper outlines the Rayleigh wave technique, presents the data and compares the predicted sections with those produced from the site surveying data. The case study illustrates the cost effectiveness of good quality Rayleigh wave measurements with straightforward site specific interpretation to quantify the extent of shallow landfill.