Based on laboratory dynamic triaxial tests

the dynamic properties of EPS （expanded polystyrene）block under various confining pressures and stress levels are studied. Tests show the dynamic stress-strain relationship of EPS is much different from that of soil. Under low confining pressure and s<0.5

dσ - dε relation is linear while it changes to hyperbolic-type under higher confining pressure. The characteristics of dε and secant dynamic shear modulus Gsec of EPS are also distinct. In the first load cycle

dε reaches a high value

and increases slowly to be almost constant. As to Gsec

it initially decreases

then increases to be stable. According to test results

40 kPa is suggested as the optimal confining pressure in application.