Constitutive Model for Explicit Numerical Modelling of Heterogeneous Massive Rocks at Excavation Boundaries Under High Stress

Rock Engineering 2009 - Rock Engineering in Difficult Conditions
Mark S Diederichs, Peter K Kaiser, Christian Frenzel,
Abstract A numerical modelling approach was developed to explicitly simulate each of three sets of geomechanical characteristics of intact rock: mineralogy, grain size and fabric type and intensity in order to investigate the contribution of the geomechanical characteristics on yielding through intact rock at excavation boundaries. This work is aimed at improving our understanding of brittle fracture initiation and propagation under high stress conditions. The approach involved creating a representative constitutive model for each of three common rock-forming minerals: mica, quartz and feldspar, estimated from literature review, then verified by an analysis of the input values compared to laboratory test results. The constitutive models developed are valid within the low confinement realm of excavation boundaries, where tensile fracture processes dominate. The mineral types were assigned to elements, which were associated with each other through an algorithm created in a finite difference model, FLAC 2D (Itasca), to simulate real crystal geometries and orientations based on rock types collected for laboratory testing and characterised through petrographic analysis. Two-dimensional models were created to represent realistic UCS and Brazilian tensile strength tests at 1:1 scale so that laboratory results could be compared to numerical model solutions. The numerical models were tested to ensure that geometry and boundary conditions, such as mesh size and loading velocity, respectively, were appropriate for the rock being modeled and minimised geometry and boundary condition dependencies. The numerical models were used in a parametric investigation of the three sets of geomechanical characteristics and compared with published observations of the rock yielding process in laboratory testing. This approach has allowed the explicit grain-scale investigation of the impact of geomechanical characteristics on rock yielding at low confinement, leading to an improved mechanistic understanding of excavation-scale rock yielding processes at excavation boundaries.
Keywords: Numerical modelling, Low Confinement, Fracture, Laboratory Strength, Constitutive Model, Finite Difference, Rock Yielding, Petrography, Geomechanical Characteristics
Full Access to Technical Paper
PDF version for $20.00
Other papers from Rock Engineering 2009 - Rock Engineering in Difficult Conditions