<p> Stress-shortening data and the micro- and macro-fabrics or experimentally
deformed calcite-cemented graywacke were analyzed in order to
understand the nature of deformation in calcite-cemented rocks. Forty four
room temperature triaxial experiments were conducted on the Blairmore
sandstone in the range of 2.1 - 19.8 percent shortening, 1 - 2600
bars confining pressure, at strain rates on the order of lo-4/second.
Under these condition, the normal transition from longitudinal fracture,
at low confining pressure, to limited homogeneous flow, at high confining
pressure is observed. The strength ( σ1, - σ3 ) increases from 2. 3
kilobars (kb) at 1 kb confining pressure (op), to 5.9 kb at 2.6 kb cp.
At low confining pressures, deformation takes place primarily by brittle
fracture of the calcitee At high confining pressures, the calcite deforms
primarily by twinning, and the sand grains deform by fracturing parallel
to σ1. The transition in deformational behavior of this rock is similar
to the transition observed in orthooalcite rocks. However, in contrast
to orthocalcite rocks, (1) strength is enhanced, (2) ductility is markedly
reduced, end (3) the brittle-ductile transition is suppressed to much
higher confining pressures. The behavior of this rock is analyzed by
considering a two-phase model material consisting of a dispersion of
strong, brittle particles within a weak and/or ductile matrix. Principles developed through the study of particulate reinforced composite engineering
materials indicate that the mechanical behavior of these materials
is dependent upon the mechanical interaction of the two phases. The
sand grains act to constrain flow of the ductile matrix. Concurrently, plastic deformation within the matrix results in the development of
stress concentrations within the nearly rigid sand grains. These
enhanced stresses may result in the initiation and propagation of
fractures within the sand grains. Propagation of the fractures is
parallel to the maximum principal stress and the fractures characteristicly
develop in this manner. Although the inherent physical properties
of the individual phases determine the strain development within
the individual phases, it is the interaction of the two phases which
determines the unique behavior of the composite material. This
behavior in turn controls the strength of the material and exerts
an important influence on the development of the deformation fabric.
The two-phase model not only provides insight into the behavior of
calcite-cemented sandstones and other analogous rocks, but also makes
it possible to predict how these rocks will behave when factors such as
temperature and strain rate are permitted to vary. </p> / Thesis / Doctor of Philosophy (PhD)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/20921 |
| Date | 05 1900 |
| Creators | Underhill, Douglas |
| Contributors | Clifford, Paul, Geology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
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