Abstract: The clinker ash is a kind of granular waste produced after the combustion of coal. It has been used in slope and foundation engineering as backfill materials. The single-particle crushing tests on the clinker ash from six different origins are carried out. The results indicate that the clinker ash particles own much lower single-particle strength than the natural sands and exhibit larger crushability. A series of drained triaxial shear tests are performed on the clinker ash to examine the effects of particle shape, degree of compaction and effective confining pressure on its shear characteristics. An increase in the degree of compaction strengthens the initial stiffness and the peak shear strength of the clinker ash. Compared to the natural sands, the clinker ash possesses larger peak friction angle and provides higher bearing capacity as foundation materials. As the effective confining pressure increases, the peak friction angle of the clinker ash gradually decreases. The results suggest that both the particle shape and the single-particle strength are important factors affecting the shear strength of the clinker ash. In addition, several particle shape parameters of the clinker ash are decided using the digital image analysis method. The clinker ash has smaller roundness and sphericity indexes due to its complex particle shape. The analysis results show that the critical state friction angle is well correlated with the particle shape parameters. A general and new particle shape index is employed to correlate with the relevant parameters associated with the critical state and its position.