 |
| Titel |
Numerical investigations on the role of micro-cracks in determining the compressive and tensile strength of rocks |
| VerfasserIn |
D. Weatherley, T. Ayton |
| Konferenz |
EGU General Assembly 2012
|
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250066058
|
|
|
|
|
|
| Zusammenfassung |
| Bonded particle models implemented using the Discrete Element Method (DEMÂ [1]) have
proven a useful numerical laboratory to investigate the interplay between geological structure
and mechanical response of rock specimens [4]. However, it is well-known that such bonded
particle models fail to reproduce the ratios of compressive:tensile strength of rocks (typically
ranging between 10:1 and 50:1). Since this strength ratio is a critical geotechnical
engineering design parameter, it is important to resolve this discrepancy between rock and
their DEM analogues.
To date, the largest compressive:tensile strength ratio achieved in DEM rock analogue
models ranges between 10:1 and 12:1Â [3]. In said studies, the compressive:tensile strength
ratio was found to depend on the number of particle bonds removed from the specimen prior
to testing; a modelling analogy for changing the micro-crack density within the specimen.
These results are consistent with the popular conjecture that the compressive and tensile
strengths of rock are impacted by the opening (or closure) of micro-cracks oriented parallel
(or perpendicular) to the loading direction.
The current research consists of a rigorous analysis of the role of micro-cracks in
governing the compressive:tensile strength ratio of DEM rock specimens. Micro-cracks are
geometrically represented as planar surfaces of variable size and orientation. Spherical
particles are packed around each planar micro-crack forming a surface that is flat on scales
larger than the particle scale. This geometrical approach permits prescription of the sizes and
orientations of micro-cracks, as well as the crack density. A series of cylindrical DEM rock
specimens are prepared with varying micro-crack densities and orientations. Specimens with
either or both micro-cracks sub-parallel to, or sub-perpendicular to the cylinder axis are
consided.
Each DEM rock specimen is subjected to both a numerical uniaxial compression test and
a numerical direct tension test. From these tests, four macroscopic material properties are
measured for each specimen: Young’s modulus, Poisson’s ratio, uniaxial compressive
strength and unixial tensile strength. Fracture mechanisms are also examined. Preliminary
results indicate that both micro-crack density and micro-crack orientation significantly impact
the macroscopic mechanical properties of DEM rock specimens. Quantitative results will be
presented at the meeting.
The software employed for these experiments is ESyS-Particle [2], an Open Source DEM
simulation package for multi-core PCs or supercomputers.
References
[1]Â Â Â Cundall, P.A, and Strack, O.D.L (1979), A discrete numerical model for
granular assemblies, Geotechnique, 29, No. 1, 47–65.
[2]Â Â Â ESyS-Particle High-Performance Discrete Element Simulation Software,
https://launchpad.net/esys-particle
[3]Â Â Â Schopfer, M.P.J, Abe, S., Childs, C. and Walsh, J.J. (2009), The impact of
porosity and crack density on the elasticity, strength and friction of cohesive
granular materials: Insights from DEM modelling, Int. J. Rock Mech. Min. Sci.,
46, 250–261.
[4]Â Â Â Weatherley, D. (2011), Investigations on the role of microstructure in brittle
failure using discrete element simulations, Geophysical Research Abstracts, 13,
EGU2011-9476. |
|
|
|
|
|
|