Characterization of municipal solid waste sites using the continuous surface wave method

The continuous surface wave system (CSWS) is a non-intrusive geophysical technique used for evaluating subsurface shear wave velocity profiles. It makes use of Rayleigh (surface) waves that propagate within a zone approximately one wavelength in depth. In ground where the stiffness changes with depth, these elastic waves are dispersive in nature, which means that they travel at a velocity that is dependent upon frequency (or wavelength). CSWS is a particularly attractive method of investigation for landfill engineering due to the non-intrusive nature of the method that eliminates many of the health and safety concerns typically associated with conventional borings for geoenvironmental investigations. This paper reports on the application of the CSWS for site characterization of municipal solid waste landfill. It is observed that the shear wave velocity profiles developed using CSWS at three different sites indicate a difference between young and old waste. However, the shear wave velocity in municipal solid waste was found to increase with depth for both young and old waste. The study also showed the ability of the CSWS to determine the cover thickness when the shear stiffness of the cover is significantly greater than that of the underlying waste.