Shear strength of a rockfill material from mine waste dumps

The slope stability of mine waste dumps is controlled by the shear strength of mining wastes which are mostly rockfill materials. Triaxial tests and direct shear tests were conducted to investigate the shear strength of a phyllite rockfill material from a mine waste dump. The behavior of the rockfill material is investigated from low to high confining pressures. The effect of soaking in acid tailings water on the shear strength of the rockfill material is studied. Particle breakage of the rockfill material increases with confining pressure. The increasing rate decreases as the confining pressure increases. An empirical equation is proposed to describe the breakage of the rockfill material. The strength of the rockfill material soaked in acid tailings water decreases with the soaking time. A new empirical strength criterion is proposed that can describe the strength change with confining pressure and particle breakage. Using the proposed strength criterion, the slope stability of the Xiyuan waste dump, the toe of which is soaked in the tailings pond, is analyzed using the Bishop method. The results show that both particle breakage and acid water damage decrease the slope stability of the mine waste dump. The analysis results also explain the appearance of cracks and settlements on the mine waste dump. The slope stability analysis of the Xiyuan waste dump indicates that the proposed strength criterion is reasonable for describing the strength of rockfill materials from low to high confining pressure. It is found that the effect of acid tailings water on the shear strength of rockfill material and the stability of the mine waste dump slope cannot be ignored.