Seismic techniques for surveying the underground of shallow foundations

For civil structures founded on shallow foundations, the ground underneath the foundation often holds the greatest risks of the total structure. In this paper the surveying of the subsurface below shallow foundations has been studied for three mayor risks; the risk of soft soils, the risk of an inhomogeneous subsurface and the risk of dangerous hidden objects.
The research question here is whether a kind of seismic technique can be used to detect those risks. As an example one could look at non-seismic wave detection techniques. There are “only-listen” detection techniques like passive sonar, infrared camera detection, and multi-microphone noise localization, but these have not been used as an example for seismic techniques in this paper. And there are “tap-and-listen” detection techniques, like active sonar, radar, echoscopy and the deep geophysical surveying techniques of the oil and gas exploration. This last technique is of course already a seismic technique in which the applied pulse or blast creates a combination of compression, shear and surface waves. These waves have all different wave velocities and will return at different time intervals. For a shallow subsurface technique though, all these waves will overlap unfortunately.
Even for a single wave technique this problem is difficult to avoid, so it is best to create a very short and single pulse. For the creation of the wave both the shortness and the singleness is very difficult. Instead of a single pulse, also single-frequency, multiple waves (constant vibration) can be used as intentional wave initiation. Then there will be even more an overlap of waves, but maybe the effects of interference and resonance can lead to positive results in the detection.
For the quantification of the risk of (dangerous) hidden objects, it can be concluded from Finite Element Calculations that the recording of the hidden objects by the “tap-and-listen” technique will very likely not work for smaller objects in an inhomogeneous subsurface. Also when we try to preserve the reflected energy as much as possible by tapping and listening at the same position on the ground surface right above the (hidden) object, it does not work. Even if we assume no frictional or viscous energy dissipation in the calculation, the relative amount of reflected energy is simply too low in comparison to the energy of the still present original wave.
This means that it will be difficult or even impossible to design good seismic techniques for surveying the underground of shallow foundations for hidden shallow objects like water pipelines, undetonated bombs, dead bodies, coffins, potholes, etc.