An application of multi-channel analysis of surface waves (MASW) to a landfill site: A case history

Abstract

The Multi-channel Analysis of Surface Waves (MASW) is used in various engineering projects to provide information on the strength of the ground. The geophysical technique spans a variety of investigations over a range of sizes; from construction of roads, railways and pipelines to the investigation of individual blocks of residential land. An MASW survey was carried out upon a closed landfill cell. The cell had been filled with waste from a city over a thirty year period and was closed some ten years ago. However, immediately adjacent landfill cells are approaching maximum airspace capacity. Several expansion plans are under consideration for the site, and the MASW survey was completed as a component of the geotechnical assessment to further these plans. The purpose of the survey was to map the original surface (or base of the fill material) and to estimate the strength of the fill material from recorded shear wave velocities. Seven seismic lines, totalling approximately 1200m was surveyed over two days of fieldwork. The interpreted dataset was displayed in 2-dimensional sections and plan-view depth slices of S-wave velocity distribution. The results showed good agreement with the subsurface profile logged at two sonic boreholes drilled through the landfill. The resultant sections were used as a primary input for the development of a 3D model for the subsequent geotechnical study that attempted to estimate the expected settlement magnitude due to a period of additional loading. This paper outlines the completed MASW survey and details how the results were used within the overall context of the project.