Abstract: Expansive soil combined with expanded polystyrene(EPS) can absorb expansive energy through deformation characteristics of EPS, improving swelling and shrinkage of expansive soil. The combination can also have excellent effect of heat preservation and vibration reduction. The dynamic stress-strain, dynamic elastic modulus and damping characteristics of EPS modified expansive soil under different conditions are studied by means of GDS dynamic triaxial instrument under different confining pressures and frequencies. The test results show that: 1)With the increase of dynamic stress, the dynamic strain and energy loss of EPS modified expansive soil increase non-linearly, while its dynamic elastic modulus decreases. 2) With the increase of frequency, the dynamic strain of EPS modified expansive soil decreases while the dynamic elastic modulus increases. 3) With the increase of confining pressure, the dynamic elastic modulus of EPS modified expansive soil decreases first and then increases. The damping ratio and dynamic stress curves of EPS modified expansive soil at different frequencies have obvious intersection points, which deviate to the left with the increase of confining pressure. When the amplitude of dynamic stress is small, applying high-frequency load will produce a larger damping ratio. In the later development period of dynamic stress, a larger damping ratio corresponds to a lower-frequency load. Under the condition of same frequency, the damping ratio of improved soil decreases with the increase of confining pressure.

Key words: expanded polystyrene(EPS), expansive soil, dynamic stress-strain, dynamic modulus of elasticity, equivalent damping ratio