What soil texture combination increases the likelihood of shrink and swell?

The correct choice is based on an understanding of how soil texture influences physical properties like shrink-swell capacity, which is the ability of soil to expand when wet and contract when dry.

Soils that are moderately fine or fine, when combined with coarse textures, often contain clay particles that are vital for shrink-swell behavior. Clay can hold water and expands when wet; this characteristic is essential in the context of shrink and swell. The presence of coarse particles in the mixture can also contribute to the overall structure and porosity of the soil, affecting how water moves in and out of the soil. When water saturates clay-rich soils, they swell significantly; upon drying, they contract, potentially leading to cracks and structural issues in the soil.

Other combinations, such as coarse and very fine, do not effectively contribute to shrink-swell behavior because very fine textures, like clay, are not present to the necessary extent to create that oscillation in moisture levels. Similarly, selecting moderately fine or fine only lacks the essential coarse texture needed to provide the conditions under which shrink-swell capacity is maximized. Finally, very coarse and medium textured soils would primarily drain water quickly, minimizing any dramatic changes in volume that typically characterize shrink-swell conditions.