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- TRIAXIAL TEST SIMULATION IN FLAC3D SERIES
- TRIAXIAL TEST SIMULATION IN FLAC3D FREE
- TRIAXIAL TEST SIMULATION IN FLAC3D CRACK
The dynamic deformation and fracturing of the rock surface are captured by high-speed 3D digital image correlation (3D-DIC), and the ultimate fracture network is characterised by X-ray computed tomography (CT). Experimental results reveal that the dynamic mechanical behaviour of rocks exhibits a clear confinement dependence on the principal pre-stresses. A recently developed triaxial Hopkinson bar (Tri-HB) system provides an alternative solution to investigate the dynamic behaviour of geomaterials under multiaxial confinement.30, 31, 32 In this apparatus, a cubic specimen is confined independently by 6 bars supported by hydraulic cylinders in three directions. However, these approaches can apply conventional triaxial confinement (σ 2 = σ 3), but cannot simulate the true triaxial and biaxial stress states. 12, 22 Then, the dynamic compression,23, 24, 25 tension, 26, 27 and shear 28, 29 behaviours of rock under coupled static and dynamic loads can be examined. To apply lateral confinement, the modifications to the SHPB test have been developed by installing hydraulic chambers or a shrink-fit sleeve.
TRIAXIAL TEST SIMULATION IN FLAC3D CRACK
The rate dependence of the following mechanical properties has been studied in the laboratory: uniaxial compressive strength,13, 14, 15 crack stress thresholds, 16 fragment distribution 17 tensile strength, 18 and fracture toughness.19, 20, 21 In addition to the strain rate effect, much effort has been devoted to determining the effect of confinement on mechanical properties, since rock and rock mass are subjected to in-situ stress conditions.
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The split Hopkinson pressure bar (SHPB) 8 or Kolsky bar 9 has been widely used to investigate the dynamic properties of various materials at high strain rates.10, 11, 12 It produces dynamic loads that deform materials over a wide range of strain rate 10 1-10 4 s −1, and a reliable interpretation of dynamic response can be achieved. Understanding the deformation and breakage behaviour of rock under dynamic loading is essential in dealing with geophysical problems and protective construction design. The increase of dynamic strength and failure strain becomes obvious at high strain rates with the enhancement of lateral confinement.ĭynamic loading occurs in many natural hazards (e.g., meteorite impacts, 1 earthquake rupture, 2 and rockfall 3) and engineering practices (e.g., rock cutting and fragmentation, 4, 5 rock burst, 6 and confined blasting 7). Both dynamic strength and peak lateral dynamic stresses increase with increasing strain rate.
TRIAXIAL TEST SIMULATION IN FLAC3D SERIES
Moreover, a series of numerical simulations is conducted to investigate the strain rate dependence of sandstone under multiaxial load conditions. Under triaxial compression, the degree of damage is substantially reduced, and microcrack localisation zones are initiated from the surface, propagate to the interior and eventually form macroscopic fractures.
TRIAXIAL TEST SIMULATION IN FLAC3D FREE
Under uniaxial compression, the specimens are broken into fragments by multiple fractures while under biaxial compression, two symmetrically distributed V-shaped damage zones form near the free surfaces. The dynamic responses of rock, including stress-strain curves, dynamic strength, energy evolutions, and damage patterns, exhibit confinement dependence, which is in good agreement with experimental observations. Then, both experimental tests and numerical modelling are carried out on sandstone under multiaxial pre-stress conditions (i.e., uniaxial, biaxial and triaxial compression) followed by dynamic loads. Firstly, the detailed numerical modelling is performed to verify some prerequisites and uncertainties in the experiments, including stress wave propagation and attenuation in three directions, dynamic stress equilibrium, boundary effects, interfacial frictions, and controversial methodologies for applying confining pressure, by using the flat-joint model and parallel bond model. In this study, a three-dimensional (3D) continuum-discrete coupled method is employed to establish a numerical-based triaxial Hopkinson bar system, and the steel bars and a cubic specimen are modelled by continuum zones and bonded-particle material, respectively. The triaxial Hopkinson bar system has been applied to investigate the responses of materials to the coupled multiaxial static-dynamic loads. Rock engineering projects at depth are frequently subjected to dynamic loadings under in-situ stress state, and the studies should be conducted to decipher the coupled effect of confining pressure and strain rate on the behaviour of rocks.