Civil defense shelters are often constructed beneath the ground to provide protection against blast loads. Concrete is widely used as the material for the defense layer of the shelters and artificial cavities are often embedded in the concrete to ensure adequate attenuation of the air-blast waves. This paper employs the Johnson-Holmquist-Concrete model, an elastoplastic damage model, to investigate the effects of artificial cavities on the attenuation of air-blast waves in the concrete defense layer. The results reveal that the peak axial stress beneath a cavity is largely reduced and the elastoplastic and damage properties of the concrete play significant roles on the wave attenuation. Two empirical formulae are then proposed to relate the decay factor of peak axial stress to the dimensions and relative positions of rectangular and circular cavities. Finally, the effects of multiple cavities on the attenuation of air-blast waves are investigated. (c) 2006 Elsevier Ltd. All rights reserved.