Simulating Intact Rock Behaviour Using Bonded Particle and Bonded Block Models Alexandr Turichshev John Hadjigeorgiou Seventh International Conference & Exhibition on Mass Mining MassMin 2016 / Sydney, NSW, 9-11 May, 2016
Introduction Synthetic rock mass (SRM) Rock mass mechanical behaviour emerges as the result of simulations No reliance on degradation of intact rock properties Bonded particle models (BPM) Simulation of intact rock behaviour Subject to significant limitations Bonded block models (BBM) Superior to BBM results have been demonstrated Majority of work was in 2D (after Esmaieli, Hadjigeorgiou and Grenon, 2010)
Bonded Particle Models (BPM) Contact stiffness Contact Particle Flow Code (PFC3D) Incompressible spherical elements balls Intact rock is simulated by particle bonding Particle Crack by rotation (after Cho, Martin and Sego, 2007) Crack by shear Bond stiffness Contact stiffness Parallel bonds allow to resist movement and rotation Clumps complex particles of arbitrary shape Parallel bond Crack by tension Particle
Bonded Particle Model Limitations Particle size dependency Models require recalibration when particle size is changed Low c / t ratio PB material calibrated to match c overestimates t Linear failure envelope Unlike in experiments on hard rock, failure envelope of PB material tends to be linear Low material friction angle Low strength gains under confining pressure Particle shape and use of parallel bonds have been identified to be the root cause associated with some of the limitations.
Bonded Block Models (BBM) DEM models based on multifaceted blocks Grain-based models (GBM) in 2D (UDEC) Tetrahedral blocks in 3D (3DEC) Blocks can be deformable Blocks can carry stress Stress/strain behaviour is governed by a constitutive model Block boundaries define discontinuities Mechanical behaviour is prescribed based on integrated models Contact Particle Crack by shear Crack by tension Particle Partial crack by rotation
Calibration Data El Teniente s (Chile) primary ore was used to calibrate models The rock is characterised by a network of mineral-filled veins Parameter Value Density 2800 kg/m 3 Young s Modulus 50 GPa Poisson s Ratio 0.28 Unconfined Compressive Strength (UCS) 125 MPa Tensile Strength 14 MPa Hoek-Brown Constant m i 9.1
Bonded Particle Simulations: Model Setup Cylindrical specimens 50 mm diameter x 125 mm long Clumped BPM approach Algorithm by Cho, Martin and Sego (2007) adapted for 3D Particle diameter: 1.5-2 mm Parallel bond bonding
Bonded Particle Simulations: Results Successful reproduction of elastic parameters Unable to match both c and t Model was calibrated to match c Overestimated t by 57% Low m i value: 7.4 vs. 9.1 targeted
Bonded Block Simulations: Model Setup Same specimen dimensions Tetrahedral blocks 5 mm edge length Zoned Linear elastic isotropic behaviour Contacts Coulomb slip model
Bonded Block Simulations: Results Successful reproduction of elastic parameters Matched both c and t Matched target m i value 9.1
Comparison between Two Types of Models Bonded Particle (BPM) Bonded Block (BBM) Excellent reproduction of elastic parameters Time consuming to calibrate Unable to match the c / t ratio Models with spherical particles and clumped models were not successful Unable to match the m i value Excellent reproduction of elastic parameters Quick and more intuitive calibration due to use of deformable blocks Excellent match to the c / t ratio Close match to the target m i value Good computational efficiency faster to run Reasonable computational efficiency Primary reasons for BBM success: blocks resist rotation, block contacts are allowed partial failure, no over-reliance on contact tensile strength
Conclusions SRM is a two-step process It is important to properly model the behaviour of intact rock Elastic parameters of intact rock can be reproduced by both BPM and BBM model types BBM was superior to BPM modelling in its ability to match c / t ratio Strength envelope BPM, however, was more efficient in computations Further development is necessary for both BPM and BBM to reach their full potential.
Acknowledgements Itasca International Inc. and Dr. Matt Pierce Mass Mining Technology 2 (MMT2) consortium The Rio Tinto Centre for Underground Mine Construction (RTC- UMC), Sudbury, Canada The Natural Sciences and Engineering Research Council of Canada (NSERC)
Thank You Questions?