Failure mechanisms and strength behaviour of foamed concrete under true triaxial compression

Foamed concrete is a lightweight and easily placed material with adjustable strength, which is promising for highway subgrade/backfill application. However, the uniaxial or conventional triaxial test cannot capture its behaviour under complex in-service multiaxial stress states. To this end, this study investigates the response of foamed concrete under true triaxial conditions with wet densities from 600 to 1000 kg/m³ under varied confining pressures. Stress-strain behaviours, energy dissipations, and failure modes were analysed, with an emphasis on the influence of the intermediate and minor principal stresses. Results show that confining pressure enhances the compressive strength, and the extent of the enhancement is determined by the ratio of the von Mises stress and the hydrostatic stress. Air void buckling dominates along the minor principal stress direction, whereas brittle shear failure prevails in both the intermediate and the minor principal stress direction. Finally, Miller’s yield criterion is shown to successfully predict the strength of foamed concrete under true triaxial loading. The scaling laws are proposed to correlate the peak stress, elastic strain energy ratio, and Miller’s model parameters with porosity. The study contributes to the knowledge of the mechanical behaviour of foamed concrete under a true triaxial stress state.