Numerical Study of the Mechanical and Hydraulic Behaviour of Blast Induced Fractures in Rocks

Abstract

This dissertation develops an integrated computational procedure using combined smoothed particle hydrodynamics (SPH) and computational fluid dynamics (CFD) to study the mechanical and hydraulic behaviour of blast induced fractures in rocks. The developed computational methods are further extended to include the large scale simulation domains in granitic rock mass for modelling the detonation of explosive in field experimental tests. The developed computational procedure is compared with the well documented experimental data in order to validate the accuracy of the proposed methodologies. A penalty based contact model between different SPH particles along with different particle resolutions in the SPH framework is proposed to effectively simulate large deformations. The performance of the penalty based contact and different particle resolutions is illustrated with a number of examples. Numerical adjustments on SPH related parameters such as tensile correction coefficient, artificial viscosity, and penalty scale factor sets are illustrated in the current research study. The procedure for obtaining the desired fracture patterns and blast induced damages using the selected constitutive material models and their calibrations in the laboratory and field scale simulations are described in detail. Then, segmentation of blast induced rocks into void and solid phases, extraction of blast induced fracture network geometry and analyse of their topological features by pore network algorithm are presented. Finally, CFD modellings are considered for the fluid flow simulations in the generated fracture networks in both laboratory and field scale simulation domains to calculate the permeability of blast induced rocks. The main findings in the current research illustrate that the SPH solution shows good convergence with increasing particle resolution. It is also found that the tensile instability stabilisation method has important effect on the solution and the use of artificial viscosity helps to spread the shock wave smoothly into the rock particles. SPH solution has the great potential for extension to the simulation of field scale blast experiments for estimations of seismic velocity, peak particle velocity, peak particle acceleration and peak detonation pressure changes. The procedures are extended in such a way that blast borehole, surrounding rock and non-reflecting boundary conditions can easily be employed. It is shown that the geometry of fracture networks is strongly dependent on coupling materials, copper as a liner inside the borehole, detonation point location, explosive column length, and borehole configurations. It is also shown that the calculated permeability depends mainly on the direction of fluid flow. Significant differences are also found between radial and axial permeability owing to the highly pore network connectivity in the radial direction. These differences are also found between lateral and axial permeability in the large scale simulation domains. Overall, this research work shows that the developed SPH method along with CFD code can be effectively combined to qualitatively and quantitatively predict the fracture network, and to calculate the permeability of blast induced rocks. The developed methodologies in SPH and CFD framework have the great potential to obtain useful information to understand the physical processes that take place in the mechanical and hydraulic behaviour of the blast induced fractures.