## 4 Discussion  
Analysis of the various field data after processing and transformation has shown that the soil structures' alteration zones have characteristics and signatures that can be depicted from field-measured ground-penetrating radar data. In the simplest field data results, the zones are depicted as areas with dearth or obliterated hyperbola diffraction, as seen in Figure 2a,b. Further probes using the attenuation characteristics also revealed significant discrepancies in the zone of distorted and undistorted soil structure (Figure 2c,d). A plausible explanation is that the high attenuation attributed to the unaltered soil structure zone may mean that the porosity, which is influenced by the structure, may have enhanced increase in the fluid content, which is one of the factors that dictates EM wave energy attenuation.  
The computed GPR signal attributes also allow for a better understanding of the continuity of the layers within both the unaltered and altered soil structure zones, as presented in Figure 3a,b. It is shown that the instantaneous phase distinguishes the distorted soil zone due to altered soil structure and zones without any impacted normal stress and, thus, may facilitate the mapping and characterization of the zones.  
Attempts to obtain more characteristic information about the interaction between the propagated GPR signals with the media around the distorted and undistorted soil zones led to the statistical plotting of the sum absolute amplitude value of the GPR signal of some parts of the 2D sections. The plots facilitated the identification of the altered regions within the section as having relatively low amplitude values as compared to the unaltered regions, which may be explained by the difference in the constituent properties of the two regions. A step further, fitting the sum absolute amplitude value plots on two adjacent profiles (altered and unaltered zones) [Figure 5a,b] also gave credence to distinguishing them. The unaltered zone has relatively higher amplitude values than the altered zone, which may be attributed to the soil structure distortions that influence the factors that control the reflectivity of the propagated EM pulse energy.  
To complement the geophysical field data interpretations, the sampled soil specimens at different depths within the test site were also analyzed and presented. The results also show trends that supported the various analyzed GPR data interpretations. For instance, the soil moisture contents tend to decline from the unaltered zone to the zone with maximum compacted impact on the surface horizon (Figure 6b). This is thought to be because of  
Figure 6: Statistical column plot of laboratory-measured soil properties at different depths and compacted effects. (**a**) Bulk density. (**b**) Moisture content. (**c**) Porosity.  
the reworked soil structures at the distorted zones, which may have caused a loss of fluid contents within the zone and, thus, influenced the media interaction with the GPR EM propagated energy. This relationship may be a diagnostic feature that may allow for the delineation of zones of altered soil structure, which may inform the useful implementation of soil utilization and management policy.