Coupling X-ray computed tomography and freeze-coring for the analysis of fine-grained low-cohesive soils

- A coupling of freeze-core sampling with millimetric X-ray CT is evaluated.
- The non-invasive X-ray CT preserves the soil core frozen for further analysis.
- The soil structure heterogeneity can be assessed based on X-ray CT data.
- A 3D model of soil bulk density categories distribution can be developed.
- Locations where soil structure is undisturbed after coring can be identified.

This paper presents the coupling of freeze-core sampling with X-ray CT scanning for the analysis of the soil structure of fine-grained, low-cohesive soils. We used a medical scanner to image the 3D soil structure of the frozen soil cores, providing X-ray CT data at a millimetric resolution over freeze-cores that are up to 62.5 cm long and 25 cm wide. The obtained data and the changes in gray level values could be successfully used to identify and characterize different soil units with distinctly different physical properties. Traditional measurements of soil bulk density, carbon and particle size analyses were conducted within each of the identified soil units. These observations were used to develop a 3D model of soil bulk density and organic matter distribution for five freeze-cores obtained at a restored floodplain in Switzerland. The millimetric X-ray CT scanning was applied to detect the impact of freeze-coring on the soil structural integrity. This allows identifying undisturbed zones, a critical precondition for any subsequent assessment of soil structure. The proposed coupling is thought to be applicable to a wide range of other low-cohesive soil types and has a large potential for applications in hydrogeology, biology or soil science.