Abstract: Taking the white strong expansive soil of Guangxi as the research object. Laboratory model test for evaporation- rainfall-evaporation is respectively carried out for expansive soil with vegetation covered or not, to explore the influence of rainfall and evaporation process on moisture-heat behavior and fissures development. The results show that, the values of radiation and surface temperature of soil sample with vegetation covered are smaller than the ones of soil sample without vegetation covered about 100 W/m2, 5-6 ℃ respectively. After rainfall process and under same evaporation conditions, the surface fissure ratio of soil samples without vegetation covered increases from 1.28% to 3.82%. Moisture content changes of surface soil increase from 3.42% to 11.17%. Drying rate of surface soil increases from 0.59%/d to 1.44%/d. The average temperature changes of surface soil increase from 13.1℃ to 14.9 ℃. Thus it can be seen, rainfall and evaporation process makes the changes of moisture content, temperature, and moisture migration rate increased. Soils tended to be broken. After rainfall process and under same evaporation conditions, obvious fissures in soil sample with vegetation covered don’t appear. Moisture content of surface soil changes from 3.16% to 2.36%. The drying rate of surface soil changes from 0.58%/d to 0.37%/d. The average temperature variation of surface soil changes from 0.58 ℃ to 0.37 ℃. Obviously, short-term rainfall and evaporation process has a low influence on the moisture holding capacity of expansive soil with vegetation covered.

Key words: expansive soil, fissure, moisture-heat, atmosphere action, vegetation