Characterisation of the internal friction angle of waste rock material from large triaxial tests using the contact dynamics method

The Chilean copper mining industry generates large amounts of waste rock materials. These structures must be designed, operated, and closed considering their physical stability. Although these structures generally do not present physical stability problems, superficial failures may occur, where waste rock material is subjected to low confining pressures. The identification of the internal friction angle, necessary for stability calculations, is based on the characterisation of these materials under high confining pressures. This assumption is not representative of the loading conditions in the superficial layers. To address this issue, numerical large-scale triaxial tests, using the contact dynamics method, are performed to identify the internal friction angle of these materials under low confining pressures. To model these material, irregular polyhedrons were generated using statistical data of crushed aggregates, considering the morphology and the particle size distribution from experimental waste rock materials. The proposed numerical approach was validated by comparing it to literature data for confining pressures over 0.5 MPa. Our results indicate that the internal friction angle stabilises at 39° for confining pressures below 0.1 MPa. This study provides important insights into the physical stability of waste rock dumps and contributes to the development of more accurate stability calculations for these structures.