Scanning electron microscope studies of an experimentally deformed graywacke sandstone

Conference · Wed Dec 01 00:00:00 EST 1976 · EOS, Trans., Am. Geophys. Union; (United States)

OSTI ID:5368372

Dengler, L A

Uniaxial-strain and uniaxial-stress tested samples of graywacke sandstone were examined with an SEM to study the relation among microstructure, dilatancy, and brittle versus ductile failure. Uniaxial-strain loading caused occasional short transgranular cracks. Clay minerals have been compacted perpendicular to the axis of maximum principal stress (sigma/sub 1/). The uniaxial strain loading path coincides with the onset of dilatancy in a uniaxial stress test and these samples should represent predilatant deformation. However, pore compaction effects are present. The density of transgranular fracturing is little increased over the unstressed rock, but the clay and matrix structure of the intergranular areas has been significantly altered. Loading to failure at less than 50 MPa confining pressure in uniaxial stress produced one or two throughgoing faults. Near the fault, a narrow zone of grain and matrix fracturing occurred. Transgranular crack formation is restricted to this zone. In some areas away from this zone, clays have been aligned at approximately 45/sup 0/ to sigma/sub 1/ and welded into continuous sheets; in other areas, clays appear undisturbed. With increased confining pressure, the width of the fractured zone increases and more grains away from this zone are fractured. At confining pressures greater than 500 MPa, a localized fault no longer occurs and sample deformation is more uniform, all grains being fractured to some degree. Clay and matrix structure has been broken down throughout the sample.

• Research Organization: Univ. of California, Livermore
• OSTI ID: 5368372
• Journal Information: EOS, Trans., Am. Geophys. Union; (United States), Vol. 57:12; Conference: AGU fall annual meeting, San Francisco, CA, USA, 6 Dec 1976
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GRAYWACKE
DEFORMATION
ELECTRON SCANNING
CLAYS
CRACKS
DUCTILE-BRITTLE TRANSITIONS
ELECTRON MICROSCOPY
FRACTURING
STRAINS
STRESSES
ELASTICITY
MECHANICAL PROPERTIES
MICROSCOPY
MINERALS
ROCKS
SEDIMENTARY ROCKS
TENSILE PROPERTIES
THERMOELASTICITY
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)