Abstract: Researches on the microscopic aspects of expansive soil are divided into qualitative researches and quantitative researches. In this paper, the microscopic measurement methods of the expansive soil are also divided into the qualitative testing methods and the quantitative testing methods. On the basis of the introduction of the electrical scanning microscope method as well as the other microscopic testing techniques are summarized. The stateoftheart progress of the microscopic study of expansive soils are also discussed in this paper. Finally, various conventional analytical methods are summarized in the paper. The following conclusions are obtained: (1) Although many quantitative testing methods are available, the researches on the microscopic structure of the expansive soil still stays in the qualitative description stage; (2) The depth of the research on the microscopic structure of the expansive is also closely related to the observation method used. Summarized from the observation approaches, it is concluded that a research trend of moving from the individual qualitative study to a combination of qualitative and quantitative approach. The quantitative approach to the soil microscopic structure might be developed in the future; (3) The method of combining with the electrical scanning microscope, mercury intrusion method and fractal theory is an effective method to study the microstructure of the expansive soils.

Key words: Expansive Soils, Microscopic Testing Methods, Analytical Method, StateoftheArt Progress, Electrical Scanning Microscope, Mercury Intrusion Method