Model representation and quantitative analysis of pore three-dimensional morphological structure based on soil computed tomography images

摘要

Computed tomography technology has contributed greatly to the visualization of soil internal structure. Complex topological structure and spatial distribution of pores have become a focal area for studying the spatiotemporal evolution of soil structure. This is significant for understanding soil functions and ecological processes. Image-processing software, such as ImageJ and Image Pro-Plus, is widely used to visualize and quantify soil pores. However, it does not account for the irregularity and heterogeneity of pore structure, leading to low segmentation accuracy and inaccurate description of pore morphology. Therefore, we used the simplified convolutional network (SCN) method to segment the pore structure and proposed a parallel thinning method to extract the pore skeleton structure. Thereafter, using three-dimensional modelling and quantitative analysis, we initially examined the spatiotemporal evolution of soil pores during freeze-thaw cycles. Based on the custom rule model and soil pore real model, we evaluated the performance of the distance transform method and parallel thinning method in extracting the pore skeleton structure. The parallel thinning method more effectively described the topological characteristics of pores, and the pore skeleton model had better centrality, refinement and connectivity. Quantitative analysis of pore characteristics illustrates that, although freeze-thaw cycles can affect pore structure at different scales, they do not regularly affect pore macroporosity and the three-dimensional fractal dimension. These results illustrate that the soil pore structure of the viscous layer is sensitive to freeze-thaw cycles and provides preliminary evidence that seasonal freeze-thaw cycles can cause a soil water retention effect and weaken resistance to erosion. This study presents a novel technique for examining soil function at the pore scale and a theoretical foundation for future research on soil structure and hydrology.