The slope stability of waste dumps is controlled by the slope angle of waste dump and the shear strength of mining wastes. Triaxial tests are conducted to investigate the shear strength of a phyllite coarse grained material from a waste dump. The behavior of the coarse grained material is investigated from low to high confining pressures. Particle breakage of the coarse grained material increases with confining pressure. The increasing rate decreases as the confining pressure increases. An empirical equation is proposed to describe the relation between pressure and breakage rate. A new empirical strength criterion is proposed that can describe the strength change with confining pressure and particle breakage. The slope stability of waste dump is analyzed using the proposed strength criterion. The result is closer to the actual condition. But the safty factor of waste dump calculated by Mohr-Coulomb criterion is relatively large and has potential risk. The slope stability analysis of the waste dump indicates that the proposed strength criterion is reasonable for describing the strength of coarse grained materials from low to high confining pressures. It is strongly recommended that the present strength criterion should be used to analyze the slope stability of high waste dumps.