GEOLOGY 1 Lecture Notes - Lecture 20: East Los Angeles College, Overburden Pressure, Flattening
Document Summary
Angle between normal to plane and 1 is , in mohr space we measure 2. Rotate in physical space from 1 axis to normal to plane. Rotate in same direction (ie. either cw or ccw) in mohr space. Rocks fail by development of fractures across which displacement -> faults . Shear stress increases until rock breaks and shear occurs along rupture. Failure envelope describes a pair of lines symmetrical about the n axis. The shear fracture envelope separates: stable from unstable states of stress. Failure envelopes: typically slightly concave to straight have a positive slope. Shear stress needed to produce failure increases with p. Angle is determined by drawing a line from center of mohr circle to point at which it intersects the shear fracture envelope at 90 degrees. Implies fractures tend to form at ~30 degrees to 1 s = c + n. Angle typically increases slightly with confining pressure.
