Quantitatively characterizing sandy soil structure altered by microbial-induced carbonate precipitation （MICP） using multi-level thresholding segmentation on synchrotron radiation imaging

Abstract The influences of biological, chemical, and flow processes on soil structure through microbial-induced carbonate precipitation (MICP) are not yet fully understood. In this study, we use the Kapur entropy (KE) multi-level thresholding segmentation algorithm to quantitatively characterize sandy soil structure altered by MICP treatment. A sandy soil specimen was treated by MICP and scanned by the synchrotron radiation micro-CT with a resolution of 6.5 µm. After validation, tri-level thresholding segmentation using KE successfully separated the precipitated calcium carbonate crystals from sand particles and pores. Spatial distribution of porosity, pore structure parameters, and flow characteristics were calculated for quantitative characterization. The size effect of the specimen was discovered to be a key factor affecting the performance of MICP treated soil. The results offer pore-scale insights of MICP treatment effect, and the quantitative understanding confirms the importance of the KE multi-level thresholding segmentation algorithm.