Investigations into the mechanism of fracture onset and growth in layered rock using physical and numerical modelling
Date
2015
Authors
Dede, Tufan
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Abstract
One of the major impediments in the field of numerical modelling in rock
mechanics is limited knowledge of the mechanisms of fracture and failure of
brittle rock. One important tool for improving the understanding of rock behaviour
is the use of laboratory experiments under controlled conditions.
The Displacement Discontinuity Method, capable of fracture growth simulation
(DIGS), has been used to model fracturing in samples under punch loading. A
Finite Difference Method, capable of plastic deformations due to its explicit time
marching scheme (FLAC), has also been used to model the punch tests.
By comparing numerical simulations with results from laboratory experiments of
punch tests, it has been possible to define the basic failure mechanism for pillar
foundation failure. Two different test set-ups were used namely, steel jacketed
axisymmetric punch tests and long strip punch tests in the triaxial cell which is
built for these specific tests.
The layered structure of the test specimens and in the test procedure had
significant effects on the fracture pattern as well as the failure load. When the
layer is near to the punch area, then both the layer and the layer conditions had a
strong effect on the failure load. When the layer was frictionless, the failure stress
dropped by about 20 percent. The same result occurred in both the axisymmetry
and strip loading tests.
When shear fractures intersect a layer with either low or high friction it
terminates. This is not the case for the tensile fractures, which can pass through
the layer media. However, it is important to note that the tensile fractures which
originate from near the cone area can not pass through the layers. They stop at the
interface.
Description
Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Engineering, 1996