The effects of porosity on the mechanics of faulting in sandstones
One hundred and forty-nine sandstone samples were deformed in a large triaxial deformation apparatus at confining pressures of 0.1, 5, 10, 30, 50, 70, and 90 MPa at a strain rate of 3 {times} 10{sup {minus}4}/sec and 25 C. Sandstones with porosities of 6.0%, 6.3%, 13.9%, 19.9%, 20.9%, 22.2%, and 27.6% were tested as whole cores for failure strength or as cores with 35{degree} or 45{degree} sawcuts for sliding friction tests. Whole cores exhibited three types of deformational behavior: (1) through going narrow shear fracture, (2) brittle-ductile transitional behavior characterized by cataclastic shear zones, and (3) pervasive ductile cataclastic flow. Mohr failure envelopes for these sandstones are concave downward with decreasing porosity increasing the initial slope of the envelope. The average coefficients of sliding friction are .575 for sawcuts and .707 for shear fractures. The Mohr failure envelopes and sliding friction data are then used to plot the range of potential slip surfaces (limiting 2 theta angles) for each sandstone. These relationships outline stability fields for reactivation of preexisting surfaces. Sandstones with preexisting fractures (or sawcuts) can exhibit four types of deformational behavior: (1) reactivation of the preexisting surface, (2) cross-cutting shear failure on a new surface, (3) brittle-ductile transitional behavior, (4) ductile cataclastic flow. High porosity sandstones (>20%) have limiting theta angles which are strongly affected by confining pressure. These sandstones exhibit all four types of deformational behavior. A series of strength versus depth profiles were generated for sandstones which indicate that the change from brittle to ductile behavior is dependent upon both initial porosity and pore pressure conditions.
- Research Organization:
- Texas Univ., Dallas, TX (USA)
- OSTI ID:
- 6742359
- Country of Publication:
- United States
- Language:
- English
Similar Records
Brittle-ductile transition in rocks
Experimental deformation in sandstone, carbonates and quartz aggregate
Related Subjects
580000* -- Geosciences
BENCH-SCALE EXPERIMENTS
BRITTLE-DUCTILE TRANSITIONS
DEFORMATION
DEPTH
DIMENSIONS
FRICTION
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
MECHANICAL PROPERTIES
PORE PRESSURE
POROSITY
PRESSURE DEPENDENCE
RESERVOIR PRESSURE
ROCKS
SANDSTONES
SEDIMENTARY ROCKS
SHEAR PROPERTIES
SLIDING FRICTION