Effect of micromechanical parameters of microstructure on compressive and tensile failure process of rock

• A comprehensive novel DEM modelling is developed to simulate rock behaviour under different stress path.
• A straightforward calibration methodology is established to reproduce real material macroscopic responses quantitatively and qualitatively.
• The relation between micro-scale parameters and macroscale responses is investigated to explore how micro-structural properties control material macroscopic response.
• The role of micro-shear and micro-tension failure events in material global rupture is examined.
• The model shows how the contribution of micro-failure events changes with rock type and the level of triaxiality.

A discrete element model is proposed to examine rock strength and failure. The model is implemented into UDEC to incorporate a new constitutive law for particle boundary behaviour. This purpose is achieved through establishing a user-defined model by creating a dynamic link library (DLL) and attaching it to the code. Rock material is represented as a collection of irregular-sized deformable particles interacting at their cohesive boundaries. The interface between two adjacent particles is viewed as a flexible contact whose constitutive law controls the material fracture and fragmentation properties. To reproduce different behaviours of rock in compression and tension, an orthotropic cohesive law is developed for contact, which allows the interfacial shear and tensile behaviours to be different from each other. The model is applied to a crystallised igneous and a soft sedimentary rock, and the individual and interactional effects of the microstructure parameters on the rocks compressive and tensile failure response are examined quantitatively and qualitatively. Statistical analysis and analytical solutions are employed to establish a methodical calibration process. It is shown that micro-shear mechanisms control rocks failure in a variety of rock types and loadings except for crystallised rocks under uniaxial compression where failure is mainly dominated by micro-tensile fractures. A practical way using the standard laboratory data is also presented to identify the controlling micro-scale failure mechanism.