Abstract: Based on analyzing the causes of information, material components and structural characters of the common expansive soil and the red clayed soil in Guangxi, some thermodynamics tests have been done on the red clayed soil and the expansive soil under normal temperature (-4 ℃-60 ℃) to search their thermodynamics characters and their relations between shear strength index and temperature. According to the tests,（σ1-σ3）peak value of the two kinds of soils do not change much under the indoor temperature (28 ℃) and the temperature of 10 ℃, 40 ℃ environment respectively, while under the temperature of 60 ℃ the change is obvious. Under the same conditions the main difference stress peak value of the red clayed soil has a greater change. The shear strength indices c,φ of two soils change with the hot state accordingly. Furthermore, the cohesive stress c of the red clayed soil and the friction angle φ of the common expansive soil are less relatively in the indoor temperature environment. From the tests we can conclude that the tendency of the thermodynamic influence on the red clayed soil and the expansive soil is similar, but the red clayed soil is more sensitive to the thermodynamic change. All these differences are caused by the genetic type and agglutinate character of the common clayed soil. The result of study offers reference for reducing the disasters and taking precautions against the calamities so as to help the construction on the red clayed soil and expansive soil area.

Key words: red clay, expansive soil, thermodynamics