Abstract: Extreme drought condition gives rise to desiccation crack in clayey soils. In nature, soil is a highly complex material which contains not only soil grains, water and air, but also some coarse particles. Nevertheless, literatures about the effects of coarse particles on desiccation crack are relatively scarce, and in particular, quantitative description of coarse particles’ impact on desiccation crack has not been reported. To reveal the influence mechanism of coarse particles on the cracking of clayey soil, desiccation cracking test was conducted on clayey soil specimens dosed with silica sand in a self-developed equipment with live camera and constant temperature and humidity. The cracking behavior and geometric fractal dimensions of surface cracks of clayey soil with coarse particles during evaporation were depicted quantitatively via computer image processing. Results unveil that: (1) coarse particles in soil increase the air entry value and make air enter the pore of soil surface prematurely by decreasing the availability of water at soil surface; (2) the water content W_C of soil when desication crack initiates has nothing to do with the content of coarse particle, but the presence or absence of coarse particles in clay would boost W_C significantly; (3) coarse particles in soil impede the development of cracks’ width while stimulates the length of cracks, and in addition, expand the area of cracks at first but lessen with the increment of coarse particle content; (4) the coefficient of fractal dimension of surface crack is positively correlated with crack rate.

Key words: clayey soil, desiccation crack, coarse particle, evaporation, fractal dimension