![]() |
Computational & Technology Resources
an online resource for computational,
engineering & technology publications |
Civil-Comp Proceedings
ISSN 1759-3433 CCP: 84
PROCEEDINGS OF THE FIFTH INTERNATIONAL CONFERENCE ON ENGINEERING COMPUTATIONAL TECHNOLOGY Edited by: B.H.V. Topping, G. Montero and R. Montenegro
Paper 167
Numerical Modelling of Blast Induced Fracture in Rock Masses A.D.R. Lima, C. Romanel and D. Roehl
Department of Civil Engineering, PUC-Rio, Catholic University of Rio de Janeiro, Brazil Full Bibliographic Reference for this paper
A.D.R. Lima, C. Romanel, D. Roehl, "Numerical Modelling of Blast Induced Fracture in Rock Masses", in B.H.V. Topping, G. Montero, R. Montenegro, (Editors), "Proceedings of the Fifth International Conference on Engineering Computational Technology", Civil-Comp Press, Stirlingshire, UK, Paper 167, 2006. doi:10.4203/ccp.84.167
Keywords: rock fracture, elastodynamics, blasting, adaptive analysis, wave propagation, finite element method.
Summary
Rock blasting is generally carried out by drilling into a rock mass, charging the
blast holes and firing the igniters located at the centre of the cylindrical charges. The
blast-induced P waves provoke high compressive stresses in the radial direction as
well as high tensile stresses in the circumferential directions. Since the problem
geometry is generally bounded by a free surface (a rock-air interface) a multiple
reflection mechanism, involving the free surface as well as the discontinuities
introduced during fracturing, will render the stress analysis a quite difficult task.
In this work the fracturing of a sound granite rock mass by blast-induced stress waves is numerically simulated by the finite element method. The rock is admitted as an isotropic and homogeneous medium that remains linear elastic until the moment of breakage, a brittle material assumption that closely corresponds to the behaviour of many sound rocks containing a high percentage of quartz. Most of the research works related to dynamic rock fragmentation considers an instantaneous fracturing mechanism determined solely on basis of the maximum stress fields generated by the explosion. This approach does not take into account some important elements that influence the fracturing process, such as the stress redistribution due to changes in the problem geometry as fractures grow, open or close in the time of analysis. The stress components in the crack tip region can be described by single-term parameters, known as stress intensity factors, whose analytical expressions are available from the linear elastic fracture mechanics for some simple cases. This work considers fracture propagation under the mixed mode I-II, provoked by P and S waves generated by the explosion itself and further wave reflections.
The fractures are assumed to grow at constant velocity less than half the shear
wave velocity [1], and along a direction
The finite element mesh, composed of quadratic triangular elements is generated
through an adaptive mesh generation procedure. The algorithm for mesh generation
is based on the "quadtree" scheme combined with a boundary triangulation
technique [2]. Once a new mesh is generated, the state variables should be
transferred from the old finite element mesh at time
The elastic stress singularity
The numerical model developed in this research presents some special features in order to simulate such a complex dynamic problem: quarter-point quadratic elements around the fracture tips, an efficient algorithm for mesh generation as fracture growth is detected, silent boundaries to represent the stress wave radiation condition, determination of the stress intensity factors and the corresponding direction of fracture propagation considering the mixed mode I-II, a penalty based contact algorithm to control fracture wall penetration, etc. References
purchase the full-text of this paper (price £20)
go to the previous paper |
|