On the use of seismic geophysical methods to characterize different soil compaction levels

To address the non-invasive way of studying soil structure and its dynamics at different scales, several geophysical techniques can complement traditional characterization methodologies. In this context, the most widespread methods for soil investigations rely on the different electrical properties of earth materials which change with the content and salinity of the incorporated fluids. Although the use of seismic methods in soil science studies is not as common as for geotechnical and reservoir characterization, seismic wave fields contain information about the mechanical properties of the subsurface and may offer insights about soil compaction that other geophysical methods cannot provide.

In this work, we evaluate the ability of seismic techniques to assess the differences between small and strong degrees of compaction in soils, relating and validating them with traditional direct measurements. The experiment was conducted at the Experimental Farm “L. Toniolo” of the University of Padova in Legnaro (northeastern Italy), under controlled conditions. The acquisition scheme was designed to resolve small-scale seismic velocity contrasts. Three different levels of induced compaction were investigated with indirect (i.e. geophysics) and direct (i.e. bulk density, texture, volumetric water content) measures.

Preliminary results of refraction and surface waves seismic analysis clearly agree with traditional direct measurements. We demonstrate that this approach is not only sensitive to the compaction phenomenon, but it allows to observe both its lateral and in-depth variability. This study opens up interesting future scenarios for geophysics to highlight the different mechanical responses caused both by soil plastic deformation and soil water distribution due to increasing compaction.