The slaking of soil crumbs as influenced by clay mineral composition

Abstract

The water adsorption and swelling of dry orientated flakes of a Ca-illite and a Ca-kaolinite have been measured at high relative vapour pressures and finally immersed in solution. Portions of the flakes equilibrated in the vapour phase were immersed in solution, either in air or under vacuum, and the degree of slaking observed. Whereas the pore space of illite was filled at p/po = 0.92 and slaking was inhibited, that of kaolinite was incompletely filled at p/po = 0.985 and the clay still slaked severely. Slaking of both clays only occurred if air was present initially in the flakes. The swelling of dry Ca-montmorillonite flakes in water was increased if the flakes were immersed in air rather than under vacuum. It is suggested that the pressures developed by entrapped air, and hence the amount of slaking due to this cause, depend not only on the initial size of the air-filled pores but also on how much the clay swells. Further, the thickness of the clay particles controls not only the pore size distribution but also how far the shear stresses due to swelling can be reduced by bending of the particles. Some of the observed properties of kaolinite flakes are explained in terms of a simple model. Two examples are given of kaolinitic soils which appear to slake and collapse to an appreciable depth on rapid wetting.