Quantifying the shear behavior of fine-grained soil with herbaceous plant roots under freeze-thaw conditions using X-ray CT scan

This study investigates the reinforcement effect of Kentucky bluegrass roots on slope soil under freeze-thaw conditions, with a focus on the Hokkaido region of Japan. Using direct shear tests combined with X-ray CT scanning, we analyzed the impact of root parameters (such as root mass and volume) on the shear strength of root-soil composites. The results revealed that freeze-thaw cycle did not cause significant root breakage or diminish the root system's ability to stabilize the soil compared to non-freeze-thaw conditions. Root-soil samples demonstrated notable ductility during shear deformation, with shear stress continuing to increase after reaching peak values. In contrast, soil samples stabilized after reaching peak shear stress without further increase. Although no significant differences in shear behavior were observed between root-soil and soil samples in the initial shearing stage, the freeze-thaw cycle led to some consolidation in root-soil samples, reducing their resistance to elastic deformation. Moreover, longer root growth periods resulted in a more pronounced increase in shear stress. CT scan image reconstruction allowed us to quantify root system parameters, such as root volume and distribution near the shear plane, which showed a strong correlation with maximum shear stress. Our findings demonstrate the effectiveness of herbaceous plant roots, particularly Kentucky bluegrass, in maintaining soil stability under freeze-thaw conditions.