Advanced numerical investigation on rock breakage with mechanical rock cutting

Mojtaba Mohammadnejad, University of Tasmania

With the rapid development of computational mechanics, numerical techniques have gradually become robust tools for the investigation of rock fracture. The aim of this study is to investigate the mechanisms of crack initiation, propagation and coalescence in mechanical rock fragmentation process using a recently developed FDEM numerical technique. The mechanism of rock failure under the action of an undercutting tool is to be simulated with a parallelized version of the combined finite−discrete element code. The ultimate goal of this project is understanding of the factors influencing the efficiency of mechanical cutting tools.

Combined finite−discrete element modelling (FEM/DEM) method

Combined FEM-DEM numerical techniques brings together the advantages of both continuum-based and discontinuum-based methods. Continuous numerical methods have flexibility in dealing with complex geometries and boundary conditions and also enjoy the well-developed constitutive models for pre-failure behaviour of rock. However, they can only deal with the fracture process up to a certain extent. The discontinuum-based methods, on the other hand, are robust techniques in modelling of block movements, explicit crack initiation and propagation, dynamic problems, while suffering drawbacks due to relying on linear failure envelope, considering low friction angle and difficulties in modelling of pre-failure behaviour of rock. Taking the advantages of two methods, FEM/DEM has been successfully employed to model problems dealing with transition process from continuum to discontinuum such as rock fracturing and fragmentation (Figure 1).

Fig 1: Modelling of transition from continuum to discontinuum behaviour of rock with combined finite−discrete element method

Model calibration

Before modelling the rock cutting process, the abilities of the purposed combined FEM/DEM code in correctly predicting the rock fracture process is investigated by simulating the failure processes in standard Brazilian indirect tensile strength (BTS) and unconfined compressive strength (UCS) tests (Figures 2 and 3).

Fig 2: Numerical calibration test for Unconfined Compressive Strength test

Fig 3: Numerical calibration test for Brazilian Tensile strength test

Simulation of rock cutting process

Once the ability of the purposed code in modelling fracture process has been validated, rock cutting process under the action of a cutting tool is simulated. The model output will be evaluated using rock cutting experiments conducted under similar conditions. The Obtained result will be used to develop a scientific basis for increasing reliability and efficiency of rock tools in mining and civil excavation applications.

Fig 4: Numerical investigation of rock cutting process

Future work

• Development and verification of three-dimensional combined FEM/DEM code
• Calibration of three dimensional numerical models
• Conducting experimental rock cutting tests
• Three dimensional modelling of rock cutting process