The influence of sand‐and silt‐size particles on the cracking during drying of small clay‐dominated aggregates

SUMMARY Shrinkage through drying is an important natural process contributing to the disintegration of clay aggregates in the field. Sand‐size particles distort the shrinkage of the surrounding clay matrix, causing the latter to shrink anisotropically until cracking ensues. Small artificial aggregates of kaolinite clay and glass beads were observed for cracking during shrinkage under ambient laboratory drying. In tests in which only single‐sized beads were present (1, 2, 3, 4 or 5 mm) the aggregates passed from a state where none cracked to that where all cracked as the concentration of beads was increased, except for 1 mm beads for which no cracking was observed. Furthermore, the concentration corresponding to the onset of cracking increased as the bead size decreased. In tests in which 3 or 5 mm beads were mixed with 1 mm beads, the same trends were observed, but increasing the 1 mm bead fraction tended to inhibit cracking. Some observations on thin clay annuli formed round solid discs complemented the aggregate results. The results provide a framework for a further study on natural soils.