Abstract：The physical properties of expansive soil and improved one are researched，and the dynamostatic triaxial tests are made on the two kind of soils. Compared with the other material，it is found that the stress-strain curve of expansive soil behaves as strain hardening，while that of improved expansive soil behaves as strain softening. The static strength and cohesion of improved expansive soil are bigger than that of expansive soil. There is a threshold of dynamical stress which divides the deformation of soil into steady-state deformation and destructive-state deformation for the two kinds of soils. The experimental formula between the cumulative plastic strain and the number of cycles of dynamic load is set up，and the dynamical stress-strain curve and dynamical elastic modulus-elastic strain curve for two kinds of soil are also studied. According to the testing results，it is not found for the frequency of dynamical load to affect the deformation of soils obviously.
