Use of x-ray tomography to investigate soil deformation around growing roots

The increased shear strength of rooted soil recently inspired researchers to assess the stability of vegetated slopes with continuum models and to design anchors by mimicking root system architectures. Yet, there is no clear understanding to date of why roots affect soil properties. This paper presents an experimental proof of concept based on x-ray tomography that addresses this issue by assessing soil microstructural changes induced by root growth. A three-dimensional time series of the root–soil interaction was imaged for 7 days. The computed local strain tensor highlights that the soil was sheared in the vicinity of the root system. Additionally, the initial bulk density of the soil was found to significantly influence the response of soil to plant root growth. In the sheared zone, the looser soil exhibited a slightly contractant behaviour, while the denser soil was purely dilatant. Further from the root system, no significant volume changes were measured for the denser specimen, whereas compaction was noted in the looser specimen. In contrast with earlier studies, results suggest that the high soil porosity near the root may result not only from steric exclusion, but also from the constitutive soil response to shear deformation.