Pore‐Size Distributions of Soils Derived using a Geometrical Approach and Multiple Resolution MicroCT Images

Abstract

Core Ideas X‐ray microtomography. An image‐based approach to determine soil pore distributions. Integration between information obtained in different spatial resolutions. Soil pores form interconnected networks that directly or indirectly influence transport processes in soils. There is great interest in estimating pore properties such as size and shape from three‐dimensional (3D) images as a way of understanding linkages between structure and function. This work evaluates the applicability of an approach to measure pore‐size distributions (PSDs) from 3D images of four soils with contrasting physical properties. Images were obtained with a benchtop X‐ray microtomograph system at spatial resolutions of 4, 6, 12, and 30 μm by varying the size of the samples from 0.5 cm to about 4 cm in diameter. Pore‐size distributions obtained at each image resolution were fitted with lognormal distribution functions with r2 ranging from 0.81 to 0.98. The four PSDs for a given soil were combined by identifying crossover points in the lognormal distributions. When pore sizes where imaged at more than one resolution, the criterion followed to eliminate redundant information was that large pore sizes are better represented in low resolution images of large sample sizes, and vice versa. Pore‐size data from four truncated PSDs were fitted with a lognormal distribution function to obtain a final (global) PSD for each soil. Global PSDs obtained with the image‐based approach correlated well with PSDs measured by mercury intrusion porosimetry and also with PSDs derived from soil water retention curves, showing potential for application of this image‐based approach to soils.