Structure of surface cracks in soil and muds

Abstract

Image analysis of photographs of surface cracks in cultivated soils for a variety of types (Vertisol, Andosol, Mollisol), and surface cracks in mud deposits shows various similar geometric characteristics. Analysis of the skeletal structure of these crack networks indicates that the relations of intersections and numbers of crack segments show a tendency to lie between those of square and hexagonal networks while the relations between particles and the number of bounding crack segments which define particle contours indicates the presence of more segments than found in a hexagonal network. Crack length distribution appears to be symmetric on log length–linear frequency co-ordinates. Area distributions of pore size or crack width indicate that the cultivated soils have a regular, symmetric distribution on log width–linear area percent occupied co-ordinates while muds have skewed distributions. Particle size abundance (defined by crack boundaries) indicates a non-linear cumulative frequency distribution on a log frequency–log size analysis that suggests non-fractal relations. Measurement of the fractal dimension of crack patterns using box counting indicates that as the porosity increases the regularity of the distribution of the cracks increases. Cultivated soils show the greatest irregularity for a given porosity. Each type of crack structure (soils, muds) has a linear relation on a porosity–fractal dimension plot. The surface area spatial characteristics of the crack network and the particles defined by them appear to be different.