The physical and numerical modelling of fracture growth in underground excavations.
Date
1998
Authors
Tomlin, Wayne
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Abstract
In the field of numerical modelling in rock mechanics, one ofthe main hindrances is the
limited knowledge ofthe mechanisms of fracturing and failure in brittle rock. A way to
increase this knowledge of rock behaviour is by carrying out laboratory experiments
under controlled conditions.
The Displacement Discontinuity Method, capable of fracture growth simulation (DIGS),
has been used to model fracturing of deep level underground excavations. In addition to
an ordinary underground mining simulation, certain geological structures have been
simulated and there influence on fracturing. The main objective of this dissertation is to
verify and calibrate DIGS by comparing results of physical experiments and numerical
simulations.
Comparing the results of the laboratory experiments and the numerical simulations of
these simulations, it has been possible to define the basic failure mechanisms around a
deep level stope, and the influence of certain geological structures. The samples used to
do the simulations were machined out of Quartzite, Black Reef Quartzite and Norite. The
tests were carried out in a biaxial cell, which was built especially for these tests.
When mining in a solid block with no geological structures present, the effect of stope
closure caused very different fracture formations when compared with the no stope
closure case. When closure of the stope occurred, the fracture s formed ahead of the face
and shear fractures were formed. When closure of the stope did not take place, the
fractures formed behind the face and the nature of the fractures were mainly tensile.
DIGS correctly simulated the same fracture pattern as was found in the physical
experiments.
When simulating the effect of a discontinuity was carried out, fracturing tended to extend
into the discontinuity, but not through the discontinuity. Evidence of activation ofthe
discontinuity was found. Simulating the effect of parting planes on fracture formation led
to the initiation of tensile fractures ahead of the face at the parting planes interface. These
results were obtained in both physical and numerical simulations.
The comparison between the physical experiments and the numerical simulations has
shown favourable results indicating that DIGS can correctly simulate fracture initiation,
fracture growth, stress conditions and stress redistribution.
Description
A dissertation Submitted to the Faculty of Engineering, University of the
Witwatersrand, Johannesburg for the degree of Master of Science.
Keywords
Fracture mechanics -- Mathematical models., Rock mechanics -- Mathematical models., Underground construction., Excavation.